Subject: [PATCH] ARM: OMAP2+: ads7846 init: fix fault caused by freeing pen-down GPIO

From: [email-masked] (Igor Grinberg)
Date: Mon, 23 Jul 2012 15:53:33 +0300

On 07/12/12 02:18, Kevin Hilman wrote:
> commit 97ee9f01d6 (ARM: OMAP: fix the ads7846 init code) mistakenly
> frees the pen-down GPIO even though it will be used by the ads7846
> driver.

But the driver requests the GPIO in ads7846_setup_pendown() method...

> 
> Freeing a GPIO means that the GPIO bank containing that GPIO can be
> runtime suspended if its the last/only GPIO being used in that bank.
> If the GPIO bank is runtime suspended, any accesses to that bank will
> cause faults.

Unless, it is requested again, or am I missing something?

> 
> Because the current code frees the GPIO, the ads7846 driver probe will
> fault when it requests its IRQ line.

But it requests that GPIO... in ads7846_setup_pendown()
prior to requesting the IRQ...

> Because the IRQ is a GPIO line,
> the request IRQ will trickle down into the OMAP GPIO layer:
> gpio_irq_type() --> _set_gpio_triggering() which can fault if the
> bank has been runtime suspended.
> 
> This is exctly what happens on Overo platforms (3530 Water, 3730 Overo
> FireSTORM) since this is the only GPIO used in the bank.
> 
> To fix, don't free the GPIO at all since it is always in use.
> 
> Cc: Igor Grinberg <[email-masked]>
> Signed-off-by: Kevin Hilman <[email-masked]>
> ---
> Tony, this applies on top of your current fixes-non-critical branch and
> should probably go in to v3.5-rc since the patch which introduced the
> problem did as well.
> 
>  arch/arm/mach-omap2/common-board-devices.c |    3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/arm/mach-omap2/common-board-devices.c b/arch/arm/mach-omap2/common-board-devices.c
> index c187586..1ae6fd6 100644
> --- a/arch/arm/mach-omap2/common-board-devices.c
> +++ b/arch/arm/mach-omap2/common-board-devices.c
> @@ -84,9 +84,6 @@ void __init omap_ads7846_init(int bus_num, int gpio_pendown, int gpio_debounce,
>  		ads7846_config.gpio_pendown = gpio_pendown;
>  	}
>  
> -	if (!board_pdata || (board_pdata && !board_pdata->get_pendown_state))
> -		gpio_free(gpio_pendown);
> -
>  	spi_register_board_info(&ads7846_spi_board_info, 1);
>  }
>  #else

-- 
Regards,
Igor.