Re: [PATCH v2] pinctrl: baytrail: Really serialize all register accesses

[Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>]

On Tue, Nov 19, 2019 at 04:46:41PM +0100, Hans de Goede wrote:
> Commit 39ce8150a079 ("pinctrl: baytrail: Serialize all register access")
> added a spinlock around all register accesses because:
> 
> "There is a hardware issue in Intel Baytrail where concurrent GPIO register
>  access might result reads of 0xffffffff and writes might get dropped
>  completely."
> 
> Testing has shown that this does not catch all cases, there are still
> 2 problems remaining
> 
> 1) The original fix uses a spinlock per byt_gpio device / struct,
> additional testing has shown that this is not sufficient concurent
> accesses to 2 different GPIO banks also suffer from the same problem.
> 
> This commit fixes this by moving to a single global lock.
> 
> 2) The original fix did not add a lock around the register accesses in
> the suspend/resume handling.
> 
> Since pinctrl-baytrail.c is using normal suspend/resume handlers,
> interrupts are still enabled during suspend/resume handling. Nothing
> should be using the GPIOs when they are being taken down, _but_ the
> GPIOs themselves may still cause interrupts, which are likely to
> use (read) the triggering GPIO. So we need to protect against
> concurrent GPIO register accesses in the suspend/resume handlers too.
> 
> This commit fixes this by adding the missing spin_lock / unlock calls.
> 
> The 2 fixes together fix the Acer Switch 10 SW5-012 getting completely
> confused after a suspend resume. The DSDT for this device has a bug
> in its _LID method which reprograms the home and power button trigger-
> flags requesting both high and low _level_ interrupts so the IRQs for
> these 2 GPIOs continuously fire. This combined with the saving of
> registers during suspend, triggers concurrent GPIO register accesses
> resulting in saving 0xffffffff as pconf0 value during suspend and then
> when restoring this on resume the pinmux settings get all messed up,
> resulting in various I2C busses being stuck, the wifi no longer working
> and often the tablet simply not coming out of suspend at all.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 39ce8150a079 ("pinctrl: baytrail: Serialize all register access")
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>

Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>