Accessing GPIO with an app

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Accessing GPIO with an app

Jerry Naidoo
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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Re: Accessing GPIO with an app

Dave McLaughlin
Good day, are you still trying to get this to work? 

I am having the same issue. From the command line via the debug interface I can use SU to go into kernel space and then export the GPIO and control it as long as I am in kernel space. If I drop back to user space, commands fail with DENIED. This seems to be related to SELINUX as I too set the directories to 777 but still get denied and the debug output shows an avc:denied message.

I've searched around and cannot find any setup for an SEPOLICY to allow GPIO file access. I did find a driver that would allow access but it requires you to build your app with the platform keys which makes debugging impossible with Android Studio.


On Thursday, 27 February 2020 22:13:33 UTC+7, Jerry Naidoo wrote:
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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Re: Accessing GPIO with an app

Donal Morrissey
Hi Dave,
Have you checked if sepolicy has recorded any attempted violations? You can use this command from the android_build directory to do so:
adb shell dmesg | grep denied | audit2allow -p out/target/product/ucm_imx8m_mini/recovery/root/sepolicy

You can also temporarily disabled sepolicy with this command:
adb shell setenforce 0

Then run the gpio commands as non-root and finally run the first command above to list any extra policies you need to add.

Building an app with platform keys in Android Studio is possible. The following is a very rough set of instructions which I've gathered together for this purpose (I've been meaning to create a blog post to cover it in detail):

// Step 1. Make sure the 'sharedUserId' is in place in the app manifest file:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 
package="com.example.developer.mysystemapp" android:sharedUserId="android.uid.system">

//Step 2. Generate the platform keystore
// Using this tool: https://github.com/getfatday/keytool-importkeypair

// In build/target/product/security
keytool
-imp -k my.keystore -p password -pk8 platform.pk8 -cert platform.x509.pem -alias platform

// Step 3. Then in android studio, add keystore to release and debug builds.

Hope these help,
Donal

On Tuesday, 26 May 2020 15:56:13 UTC+1, Dave McLaughlin wrote:
Good day, are you still trying to get this to work? 

I am having the same issue. From the command line via the debug interface I can use SU to go into kernel space and then export the GPIO and control it as long as I am in kernel space. If I drop back to user space, commands fail with DENIED. This seems to be related to SELINUX as I too set the directories to 777 but still get denied and the debug output shows an avc:denied message.

I've searched around and cannot find any setup for an SEPOLICY to allow GPIO file access. I did find a driver that would allow access but it requires you to build your app with the platform keys which makes debugging impossible with Android Studio.


On Thursday, 27 February 2020 22:13:33 UTC+7, Jerry Naidoo wrote:
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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Re: Accessing GPIO with an app

Kiran mardi
In reply to this post by Dave McLaughlin
Hi Dave/Jeranio,

Can you guys share the avc denials here, can try to get some insight into the problem.

On Tue, May 26, 2020 at 8:26 PM Dave McLaughlin <[hidden email]> wrote:
Good day, are you still trying to get this to work? 

I am having the same issue. From the command line via the debug interface I can use SU to go into kernel space and then export the GPIO and control it as long as I am in kernel space. If I drop back to user space, commands fail with DENIED. This seems to be related to SELINUX as I too set the directories to 777 but still get denied and the debug output shows an avc:denied message.

I've searched around and cannot find any setup for an SEPOLICY to allow GPIO file access. I did find a driver that would allow access but it requires you to build your app with the platform keys which makes debugging impossible with Android Studio.


On Thursday, 27 February 2020 22:13:33 UTC+7, Jerry Naidoo wrote:
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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regards,
Kiran Mardi

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Re: Accessing GPIO with an app

Dave McLaughlin
In reply to this post by Donal Morrissey
I was able to sort this out from the init.rc file by changing the permission from 0660 to 0666 for the GPIO. It also worked for the SPI and I2C buses too so I now have user-space access to them all. :) 

Thanks for the bit about creating the platform keys. If you don't mind, I'd like to add that to my blog too and credit you with the information?

I am running in debug build so the permissive mode is enabled so what I was seeing was just notifications. Good for when I switch to full SELINUX permissions. 

On Wednesday, 27 May 2020 22:06:19 UTC+7, Donal Morrissey wrote:
Hi Dave,
Have you checked if sepolicy has recorded any attempted violations? You can use this command from the android_build directory to do so:
adb shell dmesg | grep denied | audit2allow -p out/target/product/ucm_imx8m_mini/recovery/root/sepolicy

You can also temporarily disabled sepolicy with this command:
adb shell setenforce 0

Then run the gpio commands as non-root and finally run the first command above to list any extra policies you need to add.

Building an app with platform keys in Android Studio is possible. The following is a very rough set of instructions which I've gathered together for this purpose (I've been meaning to create a blog post to cover it in detail):

// Step 1. Make sure the 'sharedUserId' is in place in the app manifest file:
<manifest xmlns:android="<a href="http://schemas.android.com/apk/res/android" target="_blank" rel="nofollow" onmousedown="this.href=&#39;http://schemas.android.com/apk/res/android&#39;;return true;" onclick="this.href=&#39;http://schemas.android.com/apk/res/android&#39;;return true;">http://schemas.android.com/apk/res/android"
 
package="com.example.developer.mysystemapp" android:sharedUserId="android.uid.system">

//Step 2. Generate the platform keystore
// Using this tool: <a href="https://github.com/getfatday/keytool-importkeypair" target="_blank" rel="nofollow" onmousedown="this.href=&#39;https://www.google.com/url?q\x3dhttps%3A%2F%2Fgithub.com%2Fgetfatday%2Fkeytool-importkeypair\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFZIeQy46zzbLNLE-G6xswcZGjCAA&#39;;return true;" onclick="this.href=&#39;https://www.google.com/url?q\x3dhttps%3A%2F%2Fgithub.com%2Fgetfatday%2Fkeytool-importkeypair\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFZIeQy46zzbLNLE-G6xswcZGjCAA&#39;;return true;">https://github.com/getfatday/keytool-importkeypair

// In build/target/product/security
keytool
-imp -k my.keystore -p password -pk8 platform.pk8 -cert platform.x509.pem -alias platform

// Step 3. Then in android studio, add keystore to release and debug builds.

Hope these help,
Donal

On Tuesday, 26 May 2020 15:56:13 UTC+1, Dave McLaughlin wrote:
Good day, are you still trying to get this to work? 

I am having the same issue. From the command line via the debug interface I can use SU to go into kernel space and then export the GPIO and control it as long as I am in kernel space. If I drop back to user space, commands fail with DENIED. This seems to be related to SELINUX as I too set the directories to 777 but still get denied and the debug output shows an avc:denied message.

I've searched around and cannot find any setup for an SEPOLICY to allow GPIO file access. I did find a driver that would allow access but it requires you to build your app with the platform keys which makes debugging impossible with Android Studio.


On Thursday, 27 February 2020 22:13:33 UTC+7, Jerry Naidoo wrote:
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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Re: Accessing GPIO with an app

Rohin Malhotra
Hi Dave,

Can you post the exact line you added to init.rc for getting 0666 access to GPIO? 

On Saturday, May 30, 2020 at 12:02:13 AM UTC+5:30, Dave McLaughlin wrote:
I was able to sort this out from the init.rc file by changing the permission from 0660 to 0666 for the GPIO. It also worked for the SPI and I2C buses too so I now have user-space access to them all. :) 

Thanks for the bit about creating the platform keys. If you don't mind, I'd like to add that to my blog too and credit you with the information?

I am running in debug build so the permissive mode is enabled so what I was seeing was just notifications. Good for when I switch to full SELINUX permissions. 

On Wednesday, 27 May 2020 22:06:19 UTC+7, Donal Morrissey wrote:
Hi Dave,
Have you checked if sepolicy has recorded any attempted violations? You can use this command from the android_build directory to do so:
adb shell dmesg | grep denied | audit2allow -p out/target/product/ucm_imx8m_mini/recovery/root/sepolicy

You can also temporarily disabled sepolicy with this command:
adb shell setenforce 0

Then run the gpio commands as non-root and finally run the first command above to list any extra policies you need to add.

Building an app with platform keys in Android Studio is possible. The following is a very rough set of instructions which I've gathered together for this purpose (I've been meaning to create a blog post to cover it in detail):

// Step 1. Make sure the 'sharedUserId' is in place in the app manifest file:
<manifest xmlns:android="<a href="http://schemas.android.com/apk/res/android" rel="nofollow" target="_blank" onmousedown="this.href=&#39;http://schemas.android.com/apk/res/android&#39;;return true;" onclick="this.href=&#39;http://schemas.android.com/apk/res/android&#39;;return true;">http://schemas.android.com/apk/res/android"
 
package="com.example.developer.mysystemapp" android:sharedUserId="android.uid.system">

//Step 2. Generate the platform keystore
// Using this tool: <a href="https://github.com/getfatday/keytool-importkeypair" rel="nofollow" target="_blank" onmousedown="this.href=&#39;https://www.google.com/url?q\x3dhttps%3A%2F%2Fgithub.com%2Fgetfatday%2Fkeytool-importkeypair\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFZIeQy46zzbLNLE-G6xswcZGjCAA&#39;;return true;" onclick="this.href=&#39;https://www.google.com/url?q\x3dhttps%3A%2F%2Fgithub.com%2Fgetfatday%2Fkeytool-importkeypair\x26sa\x3dD\x26sntz\x3d1\x26usg\x3dAFQjCNFZIeQy46zzbLNLE-G6xswcZGjCAA&#39;;return true;">https://github.com/getfatday/keytool-importkeypair

// In build/target/product/security
keytool
-imp -k my.keystore -p password -pk8 platform.pk8 -cert platform.x509.pem -alias platform

// Step 3. Then in android studio, add keystore to release and debug builds.

Hope these help,
Donal

On Tuesday, 26 May 2020 15:56:13 UTC+1, Dave McLaughlin wrote:
Good day, are you still trying to get this to work? 

I am having the same issue. From the command line via the debug interface I can use SU to go into kernel space and then export the GPIO and control it as long as I am in kernel space. If I drop back to user space, commands fail with DENIED. This seems to be related to SELINUX as I too set the directories to 777 but still get denied and the debug output shows an avc:denied message.

I've searched around and cannot find any setup for an SEPOLICY to allow GPIO file access. I did find a driver that would allow access but it requires you to build your app with the platform keys which makes debugging impossible with Android Studio.


On Thursday, 27 February 2020 22:13:33 UTC+7, Jerry Naidoo wrote:
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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Re: Accessing GPIO with an app

Dave McLaughlin
I use the following in init.rc on the on boot section to set the i2c, spi, gpio etc so that they can be access in user space. Would not recommend this for a user device such as a phone but for my industrial use it works fine.

    chmod 0666 /dev/i2c-0
    chmod 0666 /dev/i2c-1
    chmod 0666 /dev/i2c-2
    chmod 0666 /dev/i2c-3
    chown system system /dev/i2c-0
    chown system system /dev/i2c-1
    chown system system /dev/i2c-2
    chown system system /dev/i2c-3

    chmod 0666 /dev/adc
    chown system system /dev/adc
    chmod 0666 /dev/pwm
    chown system system /dev/pwm

    # chmod 0666 /dev/watchdog
    # chown system system /dev/watchdog

    chown system system /sys/class/gpio/export
    chown system system /sys/class/gpio/unexport
    chmod 0666 /sys/class/gpio/export
    chmod 0666 /sys/class/gpio/unexport

    chmod 0666 /dev/spidev0.0
    chown system system /dev/spidev0.0

You can also do things like this for setting GPIO pins to know states. Here I use this to power the modem up at boot up.

# Modem power - GPIO B26 - Default ON
    write /sys/class/gpio/export 58
    write /sys/class/gpio/gpio58/direction out
    write /sys/class/gpio/gpio58/value 1
    chmod 0777 /sys/class/gpio/gpio58


Hope this helps?

Virus-free. www.avg.com

On Sat, Aug 1, 2020 at 1:11 AM Rohin Malhotra <[hidden email]> wrote:
Hi Dave,

Can you post the exact line you added to init.rc for getting 0666 access to GPIO? 

On Saturday, May 30, 2020 at 12:02:13 AM UTC+5:30, Dave McLaughlin wrote:
I was able to sort this out from the init.rc file by changing the permission from 0660 to 0666 for the GPIO. It also worked for the SPI and I2C buses too so I now have user-space access to them all. :) 

Thanks for the bit about creating the platform keys. If you don't mind, I'd like to add that to my blog too and credit you with the information?

I am running in debug build so the permissive mode is enabled so what I was seeing was just notifications. Good for when I switch to full SELINUX permissions. 

On Wednesday, 27 May 2020 22:06:19 UTC+7, Donal Morrissey wrote:
Hi Dave,
Have you checked if sepolicy has recorded any attempted violations? You can use this command from the android_build directory to do so:
adb shell dmesg | grep denied | audit2allow -p out/target/product/ucm_imx8m_mini/recovery/root/sepolicy

You can also temporarily disabled sepolicy with this command:
adb shell setenforce 0

Then run the gpio commands as non-root and finally run the first command above to list any extra policies you need to add.

Building an app with platform keys in Android Studio is possible. The following is a very rough set of instructions which I've gathered together for this purpose (I've been meaning to create a blog post to cover it in detail):

// Step 1. Make sure the 'sharedUserId' is in place in the app manifest file:
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
 
package="com.example.developer.mysystemapp" android:sharedUserId="android.uid.system">

//Step 2. Generate the platform keystore
// Using this tool: https://github.com/getfatday/keytool-importkeypair

// In build/target/product/security
keytool
-imp -k my.keystore -p password -pk8 platform.pk8 -cert platform.x509.pem -alias platform

// Step 3. Then in android studio, add keystore to release and debug builds.

Hope these help,
Donal

On Tuesday, 26 May 2020 15:56:13 UTC+1, Dave McLaughlin wrote:
Good day, are you still trying to get this to work? 

I am having the same issue. From the command line via the debug interface I can use SU to go into kernel space and then export the GPIO and control it as long as I am in kernel space. If I drop back to user space, commands fail with DENIED. This seems to be related to SELINUX as I too set the directories to 777 but still get denied and the debug output shows an avc:denied message.

I've searched around and cannot find any setup for an SEPOLICY to allow GPIO file access. I did find a driver that would allow access but it requires you to build your app with the platform keys which makes debugging impossible with Android Studio.


On Thursday, 27 February 2020 22:13:33 UTC+7, Jerry Naidoo wrote:
Hello Guys,

Without using Android Things I need to access some GPIO ports on a custom board i.e. not supported by Android things. I have gone as far as using the ADB shell toggling the IO, so I know the hardware works.
I have written some code which uses the FileWriter to send a 1 or 0 to the value file. I have also set direction to out. I created the GPIO export using ADB shell. When I do run my app I get a "Permission Denied" in the logcat.
I have tried several options e.g. changing the init.rc to add these files as 0777 permissive but the changes never seem to happen using the init.rc. I have manually set the top level sys/class/gpio >>>> all the way down to the files but still I get the permission denied error.

What am I doing wrong ? What am I missing ? I have spent 8 days reading almost every bit of information I can. I see guys doing on Raspberry PI etc and I can do it with a Raspberry PI but not with Android based project. I am using Android 9.

I don't want my app to use bluetooth or wifi to connect to another device and then control the GPIO on that external device. I want to toggle a local pin on the devices ARM processor and see an LED go on or off.

If I am missing something to tell you or you want to see my code etc, I will gladly post it it but for now any suggestions,tips or pointing to a direction I will take. Many Thanks

Kind Regards
Jeranio 

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