linux-kernel - Re: [PATCH 21/21] panel: startek-kd070fhfid015: add support of this display

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Message-ID: <39fccf61-2e48-abcf-9fd9-7bcc6ea32774@linaro.org>
Date:   Wed, 15 Mar 2023 18:12:31 +0100
From:   neil.armstrong@...aro.org
To:     Alexandre Mergnat <amergnat@...libre.com>
Cc:     Daniel Vetter <daniel@...ll.ch>, CK Hu <ck.hu@...iatek.com>,
        Jitao Shi <jitao.shi@...iatek.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Sam Ravnborg <sam@...nborg.org>,
        Rob Herring <robh+dt@...nel.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        David Airlie <airlied@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Xinlei Lee <xinlei.lee@...iatek.com>,
        Guillaume La Roque <glaroque@...libre.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org,
        Fabien Parent <fparent@...libre.com>,
        linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/21] panel: startek-kd070fhfid015: add support of this
 display

Hi,

On 15/03/2023 16:59, Alexandre Mergnat wrote:
> Hi Neil,
> 
> Le jeu. 9 mars 2023 à 15:51, Neil Armstrong
> <neil.armstrong@...aro.org> a écrit :
>>> +
>>> +#include <drm/drm_crtc.h>
>>
>> Is this include needed ?
> 
> Seems not, I remove it.
> 
>>> +     struct gpio_desc *enable_gpio;
>>> +     struct gpio_desc *reset_gpio;
>>> +     struct gpio_desc *dcdc_en_gpio;
>>
>> Isn't this "DCDC" a regulator ???
> 
> According to the panel datasheet, this is an input signal needed
> passing through TFT connector (PIN30):
> "Power IC supply enable, High active"

Ack, perhaps the name isn't the right one, or specify something like panel-dcdc.

> 
>>> +     /* Interface setting, video mode */
>>> +     ret = mipi_dsi_generic_write(dsi,
>>> +                     (u8[]){DSI_REG_IS, 0x14, 0x08, 0x00, 0x22, 0x00}, 6);
>>> +     if (ret < 0) {
>>> +             dev_err(dev, "failed to set display interface setting: %d\n",
>>> +                     ret);
>>> +             return ret;
>>> +     }
>>
>> Use mipi_dsi_generic_write_seq(dsi, DSI_REG_IS, 0x14, 0x08, 0x00, 0x22, 0x00); instead,
>> it's simpler and doesn't need explicit return check.
> 
> "mipi_dsi_generic_write_seq" doesn't exist but I will add it below
> "mipi_dsi_dcs_write_seq" in drm_mipi_dsi.h

It is now https://github.com/torvalds/linux/blob/master/include/drm/drm_mipi_dsi.h#L302 since a9015ce59320

> I must keep the return check to jump out of "stk_panel_init" if
> something goes wrong, but I can drop the error print.

The mipi_dsi_generic_write_seq & mipi_dsi_dcs_write_seq macros does the return check for free.

> 
>>> +static int stk_panel_enable(struct drm_panel *panel)
>>> +{
>>> +     struct stk_panel *stk = to_stk_panel(panel);
>>> +
>>> +     if (stk->enabled)
>>> +             return 0;
>>> +
>>> +     backlight_enable(stk->backlight);
>>> +
>>> +     stk->enabled = true;
>>> +
>>> +     return 0;
>>> +}
>>
>> Is this really needed ? the backlight core will enable it automatically.
> 
> Ok, it's managed by drm_panel.c driver.
> Then I can also remove stuff from stk_panel_disable.
> 
> 
> Regards,
> Alex