Re: [PATCH 07/11] hw/gpio/pl061: Make pullup/pulldown of outputs configurable

[Richard Henderson <richard.henderson@linaro.org>]

On 7/2/21 3:40 AM, Peter Maydell wrote:
> The PL061 GPIO does not itself include pullup or pulldown resistors
> to set the value of a GPIO line treated as an output when it is
> configured as an input (ie when the PL061 itself is not driving it).
> In real hardware it is up to the board to add suitable pullups or
> pulldowns.  Currently our implementation hardwires this to "outputs
> pulled high", which is correct for some boards (eg the realview ones:
> see figure 3-29 in the "RealView Platform Baseboard for ARM926EJ-S
> User Guide" DUI0224I), but wrong for others.
> 
> In particular, the wiring in the 'virt' board and the gpio-pwr device
> assumes that wires should be pulled low, because otherwise the
> pull-to-high will trigger a shutdown or reset action.  (The only
> reason this doesn't happen immediately on startup is due to another
> bug in the PL061, where we don't assert the GPIOs to the correct
> value on reset, but will do so as soon as the guest touches a
> register and pl061_update() gets called.)
> 
> Add properties to the pl061 so the board can configure whether it
> wants GPIO lines to have pullup, pulldown, or neither.
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   hw/gpio/pl061.c | 51 +++++++++++++++++++++++++++++++++++++++++++++----
>   1 file changed, 47 insertions(+), 4 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~