Re: [PATCH/RFC] ARM: dts: armadillo800eva: Split LCD mux and gpio

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Geert,

Thank you for the patch.

On Wednesday 24 May 2017 13:43:34 Geert Uytterhoeven wrote:
> Configuration of the lcd0 pinmux group and GPIO hog for the external
> GPIO mux are done using a single device node, causing the "output-high"
> property to be applied to both.  This will fail for the pinmux group,
> but doesn't cause any harm, as the failure is ignored silently.
> 
> However, after "pinctrl: sh-pfc: propagate errors on group config", the
> failure will become fatal, leading to a broken display:
> 
>     sh-pfc e6050000.pin-controller: pin_config_group_set op failed for group
> 102 sh-pfc e6050000.pin-controller: Error applying setting, reverse things
> back sh-pfc e6050000.pin-controller: failed to select default state
> 
> Split the configuration in two subnodes, and replace the GPIO hog by a
> pull-up pin bias to fix this.
> 
> Fixes: ffd2f9a5afb730b9 ("ARM: shmobile: armadillo800eva dts: Add pinctrl
> and gpio-hog for lcdc0") Signed-off-by: Geert Uytterhoeven
> <geert+renesas@glider.be>
> ---
> This is a hard dependency for "pinctrl: sh-pfc: propagate errors on
> group config" (https://patchwork.kernel.org/patch/9186713/).
> 
> Notes:
>   1. Just keeping the GPIO hog doesn't work, as the sh-pfc driver
>      requires each pinctrl (sub)node to have at least one "pins" or
>      "groups" property,
>   2. Keeping "output-high" doesn't work, as the sh-pfc driver does not
>      implement PIN_CONFIG_OUTPUT.
> 
> Should I fix 1 and/or 2 instead?
> ---
>  arch/arm/boot/dts/r8a7740-armadillo800eva.dts | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm/boot/dts/r8a7740-armadillo800eva.dts
> b/arch/arm/boot/dts/r8a7740-armadillo800eva.dts index
> 44b335b9f035436d..7feedc86f6915654 100644
> --- a/arch/arm/boot/dts/r8a7740-armadillo800eva.dts
> +++ b/arch/arm/boot/dts/r8a7740-armadillo800eva.dts
> @@ -267,13 +267,16 @@
>  	};
> 
>  	lcd0_pins: lcd0 {
> -		groups = "lcd0_data24_0", "lcd0_lclk_1", "lcd0_sync";
> -		function = "lcd0";
> +		mux {
> +			groups = "lcd0_data24_0", "lcd0_lclk_1", "lcd0_sync";
> +			function = "lcd0";
> +		};
> 
> -		/* DBGMD/LCDC0/FSIA MUX */
> -		gpio-hog;
> -		gpios = <176 0>;
> -		output-high;
> +		gpio {
> +			/* DBGMD/LCDC0/FSIA MUX */
> +			pins = "PORT176";
> +			bias-pull-up;

The signal is pulled low through a 10kΩ resistor, so a pull-up is a bit weak. 
You'll end up with an intermediate voltage level that could result in meta-
stability and/or latch-up. I think we need to really drive the output to 1.

> +		};
>  	};
>  };

-- 
Regards,

Laurent Pinchart