Jon,
On Thu, Oct 18, 2012 at 02:42:01, Hunter, Jon wrote:
> Hi Gururaja,
>
> On 10/17/2012 01:13 AM, Hebbar, Gururaja wrote:
> > Hi,
> >
> > I came across a peculiar issue while updating GPIO debounce registers on
> > OMAP platform.
> >
> > According to mainline commit ae547354a8ed59f19b57f7e1de9c7816edfc3537
> >
> > gpio/omap: save and restore debounce registers
> >
> > GPIO debounce registers need to be saved and restored for proper functioning
> > of driver.
> >
> > ...
> > @@ -1363,6 +1369,12 @@ static void omap_gpio_restore_context(struct gpio_bank *bank)
> > __raw_writel(bank->context.fallingdetect,
> > bank->base + bank->regs->fallingdetect);
> > __raw_writel(bank->context.dataout, bank->base + bank->regs->dataout);
> > + if (bank->dbck_enable_mask) {
> > + __raw_writel(bank->context.debounce, bank->base +
> > + bank->regs->debounce);
> > + __raw_writel(bank->context.debounce_en,
> > + bank->base + bank->regs->debounce_en);
> > + }
> > }
> >
> >
> > Due to copy/paste of this commit into my local tree, I missed the check for
> > bank->dbck_enable_mask, and directly restored the saved value from context.
> >
> > After this, I saw random crashes when accessing different registers (sometimes
> > its OE register and sometime its DATAOUT register).
> >
> > These crashes were seen across 2nd and subsequent suspend/resume.
> >
> > My doubt/questions are
> > 1. Why should debounce registers be updated only when it's accessed previously?
>
> If debounce is not being used by any of the gpios, then there is no need
> to restore them as there are no bits set. So this makes sense and saves
> a couple register writes.
What I want to know is that other than saving register writes, is there any
other important stuff that specifies this requirement.
>
> > 2. What is the relation between updating debounce registers and crash seen on
> > others registers?
>
> This I am not sure about. I gave this a quick try on my omap3430 beagle
> board, but I did not see any side-effects from doing this. However, if
> you are always restoring the debounce context regardless of whether
> debounce is being used, then you could be writing bad values to the
> debounce registers as the context variables bank->context.debouce and
> bank->context.debouce_en may not initialised. So that is bad. However,
> that said I am still not sure how this could cause a crash.
>
> Can you share more details on ...
Sorry for missing below details in first post.
> 1. The OMAP platform you are using?
I was trying this on TI AM335x platform (repo below). On AM335x EVM board
http://arago-project.org/git/projects/?p=linux-am33x.git;a=shortlog;
h=refs/heads/v3.2-staging
> 2. What linux distro/environment you are using?
Arago AM335x PSP release (linux 3.2 + am335x patch-set)
> 3. If there are any specific steps to reproduce this 100% of the time?
On top of this tree, try suspend/resume using "echo mem > /syspower/state"
>
> Cheers
> Jon
>
Regards,
Gururaja
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