linux-kernel - Re: [PATCH v2 3/4] ARM: dts: omap: omap4-epson-embt2ws: add unknown gpio outputs

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Message-ID: <20241011111212.1b935eb8@akair>
Date: Fri, 11 Oct 2024 11:12:12 +0200
From: Andreas Kemnade <andreas@...nade.info>
To: Roger Quadros <rogerq@...nel.org>
Cc: linux-kernel@...r.kernel.org, Rob Herring <robh@...nel.org>,
 linux-omap@...r.kernel.org, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 tony@...mide.com, devicetree@...r.kernel.org, khilman@...libre.com, Conor
 Dooley <conor+dt@...nel.org>, aaro.koskinen@....fi
Subject: Re: [PATCH v2 3/4] ARM: dts: omap: omap4-epson-embt2ws: add unknown
 gpio outputs

Am Thu, 10 Oct 2024 23:15:51 +0300
schrieb Roger Quadros <rogerq@...nel.org>:

> On 10/10/2024 15:29, Andreas Kemnade wrote:
> > Set them to the state seen in a running system, initialized
> > by vendor u-boot or kernel. Add line names where they are defined
> > in the vendor kernel.
> > gpio15 resets something in the display, otherwise meaning of the
> > gpios is not known.
> > 
> > Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> > ---
> >  .../boot/dts/ti/omap/omap4-epson-embt2ws.dts  | 92
> > +++++++++++++++++++ 1 file changed, 92 insertions(+)
> > 
> > diff --git a/arch/arm/boot/dts/ti/omap/omap4-epson-embt2ws.dts
> > b/arch/arm/boot/dts/ti/omap/omap4-epson-embt2ws.dts index
> > 7684868a2eed..983a21d95db3 100644 ---
> > a/arch/arm/boot/dts/ti/omap/omap4-epson-embt2ws.dts +++
> > b/arch/arm/boot/dts/ti/omap/omap4-epson-embt2ws.dts @@ -115,6
> > +115,73 @@ wl12xx_vmmc: wl12xx-vmmc { };
> >  };
> >  
> > +&gpio1 {
> > +	pinctrl-names = "default";
> > +	pinctrl-0 = <&gpio1_hog_pins &gpio1wk_hog_pins>;
> > +
> > +	lb-reset-hog {
> > +		gpio-hog;
> > +		gpios = <9 GPIO_ACTIVE_HIGH>;
> > +		output-low;
> > +		line-name = "lb_reset";
> > +	};
> > +
> > +	power-en-hog {
> > +		gpio-hog;
> > +		gpios = <10 GPIO_ACTIVE_HIGH>;
> > +		output-high;
> > +		line-name = "power_en";
> > +	};  
> 
> As GPIO 9 and 10 come form the Wake-up domain, my guess is 
> they are used as wake-up input source. Reset button / Power off/wake
> button? From pinmux they seem to be Input. So why do we need to force
> them to a certain output state?

Interesting reasoning and good to bring up those thoughts.

Vendor v3.0 kernel:
shell@...roid:/sys/kernel/debug # cat gpio 
GPIOs 0-31, gpio:
[...]
 gpio-9   (gpio_lb_reset       ) out lo
 gpio-10  (gpio_power_en       ) out hi

So they are configured as output.
There is one power button. It can be handled via the TWL6032 (driver
not upstreamed yet). There is also one reset button resetting the SoC.

I do not see a reason why to deviate from vendor kernel.
 
> Can you please confirm if everything works as usual without this hog?
> 
Well, if everything is working well, I would agree to optimize
these things. But not now. There are races in the boot process
and I would like to rule out that any random or strange behavior has
anything to do with some gpio setting.

Regards,
Andreas