Subject: [PATCH] gpio/omap: fix invalid context restore of gpio bank-0

From: [email-masked] (Kevin Hilman)
Date: Mon, 02 Jul 2012 11:07:44 -0700

+ Neil Brown

Hi Jon,

Jon Hunter <[email-masked]> writes:

> Currently the gpio _runtime_resume/suspend functions are calling the
> get_context_loss_count() platform function if the function is populated for
> a gpio bank. This function is used to determine if the gpio bank logic state
> needs to be restored due to a power transition. This function will be populated
> for all banks, but it should only be called for banks that have the
> "loses_context" variable set. It is pointless to call this if loses_context is
> false as we know the context will never be lost and will not need restoring.
>
> For all OMAP2+ devices gpio bank-0 is in an always-on power domain and so will
> never lose context. We found that the get_context_loss_count() was being called
> for bank-0 during the probe and returning 1 instead of 0 indicating that the
> context had been lost. This was causing the context restore function to be
> called at probe time for this bank and because the context had never been saved,
> was restoring an invalid state. This ultimately resulted in a crash [1].
>
> There are multiple bugs here that need to be addressed ...
>
> 1. Why the always-on power domain returns a context loss count of 1? This needs
>    to be fixed in the power domain code. However, the gpio driver should not
>    assume the loss count is 0 to begin with.
> 2. The omap gpio driver should never be calling get_context_loss_count for a
>    gpio bank in a always-on domain. This is pointless and adds unneccessary
>    overhead.
> 3. The OMAP gpio driver assumes that the initial power domain context loss count
>    will be 0 at the time the gpio driver is probed. However, it could be
>    possible that this is not the case and an invalid context restore could be
>    performed during the probe. To avoid this otherwise only populated the

The 'To avoid this...' sentence here doesn't read well.  Looks like you
need to:

s/otherwise//
s/populated/populate/

?

>    get_context_loss_count() function pointer after the initial call to
>    pm_runtime_get() has occurred. This will ensure that the first
>    pm_runtime_put() initialised the loss count correctly.
>
> This patch addresses issues 2 and 3 above.
> [1] http://marc.info/?l=linux-omap&m=134065775323775&w=2
>
> Cc: Grant Likely <[email-masked]>
> Cc: Linus Walleij <[email-masked]>
> Cc: Kevin Hilman <[email-masked]>
> Cc: Tarun Kanti DebBarma <[email-masked]>
> Cc: Franky Lin <[email-masked]>
>
> Reported-by: Franky Lin <[email-masked]>
> Signed-off-by: Jon Hunter <[email-masked]>

Thanks for digging inot this bug Jon.  The same bug was brought up by
Neil Brown (Cc'd) in a different thread.

Neil, it looks to me that this fix will address the problems you were
seeing as well.  Care to test, and respond with your ack/tested-by if it
works for you?  Thanks.

Kevin

> ---
>  drivers/gpio/gpio-omap.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
> index c4ed172..f13fc9c 100644
> --- a/drivers/gpio/gpio-omap.c
> +++ b/drivers/gpio/gpio-omap.c
> @@ -1081,7 +1081,6 @@ static int __devinit omap_gpio_probe(struct platform_device *pdev)
>  	bank->is_mpuio = pdata->is_mpuio;
>  	bank->non_wakeup_gpios = pdata->non_wakeup_gpios;
>  	bank->loses_context = pdata->loses_context;
> -	bank->get_context_loss_count = pdata->get_context_loss_count;
>  	bank->regs = pdata->regs;
>  #ifdef CONFIG_OF_GPIO
>  	bank->chip.of_node = of_node_get(node);
> @@ -1135,6 +1134,9 @@ static int __devinit omap_gpio_probe(struct platform_device *pdev)
>  	omap_gpio_chip_init(bank);
>  	omap_gpio_show_rev(bank);
>  
> +	if (bank->loses_context)
> +		bank->get_context_loss_count = pdata->get_context_loss_count;
> +
>  	pm_runtime_put(bank->dev);
>  
>  	list_add_tail(&bank->node, &omap_gpio_list);