linux-kernel - Re: [PATCH] drm/panel: samsung-s6d7aa0: transition to mipi

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Message-ID: <CAD=FV=Xk6hYmJGLhW2ruvWwOETfmCAQX000WX4LrC3CPCZJMJQ@mail.gmail.com>
Date: Mon, 17 Mar 2025 09:26:54 -0700
From: Doug Anderson <dianders@...omium.org>
To: Tejas Vipin <tejasvipin76@...il.com>
Cc: neil.armstrong@...aro.org, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch, 
	aweber.kernel@...il.com, quic_jesszhan@...cinc.com, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	asrivats@...hat.com
Subject: Re: [PATCH] drm/panel: samsung-s6d7aa0: transition to mipi_dsi
 wrapped functions

Hi,

On Sat, Mar 15, 2025 at 9:50 PM Tejas Vipin <tejasvipin76@...il.com> wrote:
>
> @@ -62,93 +62,66 @@ static void s6d7aa0_reset(struct s6d7aa0 *ctx)
>         msleep(50);
>  }
>
> -static int s6d7aa0_lock(struct s6d7aa0 *ctx, bool lock)
> +static void s6d7aa0_lock(struct s6d7aa0 *ctx, struct mipi_dsi_multi_context *dsi_ctx, bool lock)
>  {
> -       struct mipi_dsi_device *dsi = ctx->dsi;
> +       if (dsi_ctx->accum_err)
> +               return;

nit: I don't think you need this extra check, do you? The entire
function is "multi" calls so just let them be no-ops. It may seem like
an optimization to have the extra check at the start of the function,
but it's better to optimize for the "no error" case and let the
"error" case be a little slower.

>  static int s6d7aa0_on(struct s6d7aa0 *ctx)
>  {
>         struct mipi_dsi_device *dsi = ctx->dsi;
> -       struct device *dev = &dsi->dev;
> -       int ret;
> +       struct mipi_dsi_multi_context dsi_ctx = { .dsi = dsi };
>
> -       ret = ctx->desc->init_func(ctx);
> -       if (ret < 0) {
> -               dev_err(dev, "Failed to initialize panel: %d\n", ret);
> +       ctx->desc->init_func(ctx, &dsi_ctx);
> +       if (dsi_ctx.accum_err < 0)
>                 gpiod_set_value_cansleep(ctx->reset_gpio, 1);
> -               return ret;
> -       }
>
> -       ret = mipi_dsi_dcs_set_display_on(dsi);
> -       if (ret < 0) {
> -               dev_err(dev, "Failed to set display on: %d\n", ret);
> -               return ret;
> -       }
> +       mipi_dsi_dcs_set_display_on_multi(&dsi_ctx);
>
> -       return 0;
> +       return dsi_ctx.accum_err;

Not something new to your patch, I wonder if the setting of the reset
GPIO should actually be _below_ the call to turn the display on. Seems
like if that fails you should also be setting the reset GPIO. That
would be a change in behavior but seems more correct?

Given that it's a change in behavior, I'd be OK w/ leaving it as-is or
changing it (and mentioning it in the commit message). I'd be curious
if anyone else has opinions here.

...oh, actually, you should just delete the reset GPIO stuff from this
function. The one caller of this function is already setting the reset
GPIO, right?

Everything else looks good to me.

-DOug