Re: [PATCH 2/8] gpio: tqmx86: introduce shadow register for GPIO output value

[Andrew Lunn <andrew@xxxxxxx>]

On Wed, May 29, 2024 at 09:45:14AM +0200, Matthias Schiffer wrote:
> The TQMx86 GPIO controller uses the same register address for input and
> output data. Reading the register will always return current inputs
> rather than the previously set outputs (regardless of the current
> direction setting). Therefore, using a RMW pattern does not make sense
> when setting output values. Instead, the previously set output register
> value needs to be stored as a shadow register.
> 
> As there is no reliable way to get the current output values from the
> hardware, also initialize all channels to 0, to ensure that stored and
> actual output values match. This should usually not have any effect in
> practise, as the TQMx86 UEFI sets all outputs to 0 during boot.
> 
> Also prepare for extension of the driver to more than 8 GPIOs by using
> DECLARE_BITMAP.
> 
> Fixes: b868db94a6a7 ("gpio: tqmx86: Add GPIO from for this IO controller")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>

Reviewed-by: Andrew Lunn <andrew@xxxxxxx>

    Andrew