Introduction

The Android Linux driver was published here:

https://github.com/goodix/gt9xx_driver_android

After reading the code, it is found that when irq-gpios is not set, the code will be working in polling mode. However when I tried to port it to Android 9.0. The code crashes.

kernel/kernel/locking/rtmutex.c:1536: (discriminator 9) [<ffffff8008b538a8>] rt_mutex_trylock+0x30/0xb8
kernel/drivers/i2c/i2c-core.c:2343: [<ffffff80086b1a98>] i2c_transfer+0x40/0x94
kernel/drivers/input/touchscreen/gt9xx/gt9xx.c:97: [<ffffff800868da2c>] gtp_i2c_read+0xf4/0x1a8
kernel/drivers/input/touchscreen/gt9xx/gt9xx.c:355: [<ffffff800868e198>] gtp_get_points+0x84/0x284
kernel/drivers/input/touchscreen/gt9xx/gt9xx.c:569: [<ffffff800868e540>] gtp_work_func+0x1a8/0x5ec
kernel/include/linux/hrtimer.h:393: [<ffffff800868e99c>] gtp_timer_handler+0x18/0x40
kernel/kernel/time/hrtimer.c:1261: [<ffffff800810965c>] __hrtimer_run_queues+0x138/0x350
kernel/kernel/time/hrtimer.c:1362: [<ffffff8008109da8>] hrtimer_interrupt+0xa0/0x1b0
kernel/drivers/clocksource/arm_arch_timer.c:150: [<ffffff80087a5610>] arch_timer_handler_virt+0x28/0x3c
kernel/kernel/irq/chip.c:761: [<ffffff80080f99c4>] handle_percpu_devid_irq+0x7c/0x1d0
kernel/kernel/irq/irqdesc.c:352: [<ffffff80080f53dc>] generic_handle_irq+0x18/0x2c
kernel/kernel/irq/irqdesc.c:388: [<ffffff80080f5710>] __handle_domain_irq+0xa8/0xac
kernel/drivers/irqchip/irq-gic.c:352: [<ffffff8008080f24>] gic_handle_irq+0x64/0xa0

Above indicates that the gtp_work_func() could not work in interrupt context. Hence it is believed that the interrupt mode of this driver does not work as well.

Fix the problem

To fix the problem, the gtp_work_func has to be moved to non-interrupt context. The first idea is to use the work queue. The original driver, uses hrtimer (high resolution timer) to trigger timer, which for me, however it does not make sense, as the I2C reading does not have to be that accurate in terms of timing. We could simply uses delayed work queue to replace the hrtimer solution.

The fix is put at:

https://github.com/pandysong/gt9xx_driver_android

Improvement

Further improvement were also done

• Make the interrupt mode working as well (not tested, as I have only polling mode test bed)
• Fix some compilation error.
• Add dts setting goodix,mirror-x goodix,mirror-y to allow mirroring the position.

TBD

Further improvement could be done in the future:

• improve document (allowing polling mode, add mirror-x and mirror-y dts