linux-kernel - Re: [PATCH v4 8/8] drm/panel: nt35510: support FRIDA FRD400B25025-A-CTK

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Message-ID: <CABGWkvoNuJNmxhrOE6csE2mGwF50ou-jx-kpmH-oQ2zBgzLrSg@mail.gmail.com>
Date: Sat, 6 Jan 2024 12:07:00 +0100
From: Dario Binacchi <dario.binacchi@...rulasolutions.com>
To: Linus Walleij <linus.walleij@...aro.org>
Cc: linux-kernel@...r.kernel.org, linux-amarula@...rulasolutions.com, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, Daniel Vetter <daniel@...ll.ch>, 
	David Airlie <airlied@...il.com>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Sam Ravnborg <sam@...nborg.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 8/8] drm/panel: nt35510: support FRIDA FRD400B25025-A-CTK

On Fri, Jan 5, 2024 at 8:09 PM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> On Thu, Jan 4, 2024 at 9:42 AM Dario Binacchi
> <dario.binacchi@...rulasolutions.com> wrote:
>
> > The initialization commands are taken from the STMicroelectronics driver
> > found at [1].
> > To ensure backward compatibility, flags have been added to enable gamma
> > correction setting and display control. In other cases, registers have
> > been set to their default values according to the specifications found
> > in the datasheet.
> >
> > [1] https://github.com/STMicroelectronics/STM32CubeF7/blob/master/Drivers/BSP/Components/nt35510/
> > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> >
> > ---
> >
> > (no changes since v2)
>
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> (also tested to not regress my hardware)

After submitting v4, I tested the driver under different conditions,
i. e. without enabling display support in
U-Boot (I also implemented a version for U-Boot, which I will send
only after this series is merged into
the Linux kernel). In that condition I encountered an issue with the reset pin.

The minimal fix, would be this:

diff --git a/drivers/gpu/drm/panel/panel-novatek-nt35510.c
b/drivers/gpu/drm/panel/panel-novatek-nt35510.c
index c85dd0d0829d..89ba99763468 100644
--- a/drivers/gpu/drm/panel/panel-novatek-nt35510.c
+++ b/drivers/gpu/drm/panel/panel-novatek-nt35510.c
@@ -1133,7 +1133,7 @@ static int nt35510_probe(struct mipi_dsi_device *dsi)
        if (ret)
                return ret;

-       nt->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_ASIS);
+       nt->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
        if (IS_ERR(nt->reset_gpio)) {
                dev_err(dev, "error getting RESET GPIO\n");
                return PTR_ERR(nt->reset_gpio);

With the doubt that this might cause a regression in your use case.

I then tried modifying the device tree instead of the nt35510 driver.
In the end, I arrived
at this patch that leaves me with some doubts, especially regarding
the strict option.

diff --git a/arch/arm/boot/dts/st/stm32f769-disco-mb1225-revb03-mb1166-reva09.dts
b/arch/arm/boot/dts/st/stm32f769-disco-mb1225-revb03-m>
index 014cac192375..32ed420a6cbf 100644
--- a/arch/arm/boot/dts/st/stm32f769-disco-mb1225-revb03-mb1166-reva09.dts
+++ b/arch/arm/boot/dts/st/stm32f769-disco-mb1225-revb03-mb1166-reva09.dts
@@ -13,6 +13,17 @@ &panel0 {
        compatible = "frida,frd400b25025", "novatek,nt35510";
        vddi-supply = <&vcc_3v3>;
        vdd-supply = <&vcc_3v3>;
+       pinctrl-0 = <&panel_reset>;
+       pinctrl-names = "default";
        /delete-property/backlight;
        /delete-property/power-supply;
 };
+
+&pinctrl {
+       panel_reset: panel-reset {
+               pins1 {
+                       pinmux = <STM32_PINMUX('J', 15, GPIO)>;
+                       output-high;
+               };
+       };
+};

diff --git a/drivers/pinctrl/stm32/pinctrl-stm32.c
b/drivers/pinctrl/stm32/pinctrl-stm32.c
index 346a31f31bba..6f055f7f96a2 100644
--- a/drivers/pinctrl/stm32/pinctrl-stm32.c
+++ b/drivers/pinctrl/stm32/pinctrl-stm32.c
@@ -895,7 +895,6 @@ static const struct pinmux_ops stm32_pmx_ops = {
        .set_mux                = stm32_pmx_set_mux,
        .gpio_set_direction     = stm32_pmx_gpio_set_direction,
        .request                = stm32_pmx_request,
-       .strict                 = true,
 };

Another option to fix my use case without introducing regressions
could be to add a
new property to the device tree that suggests whether to call
devm_gpiod_get_optional()
with the GPIOD_ASIS or GPIOD_OUT_HIGH parameter.

What is your opinion?

Thanks and regards,
Dario Binacchi

>
> Yours,
> Linus Walleij



-- 

Dario Binacchi

Senior Embedded Linux Developer

dario.binacchi@...rulasolutions.com

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