linux-kernel - Re: [PATCH v2 2/3] drm: Add MIPI support function and macros

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Message-ID: <CAD=FV=VLoMenu22F_VeoHyfXwRO7JfXL8peQLEpkqeZ1tDOmEQ@mail.gmail.com>
Date: Tue, 29 Jul 2025 14:34:24 -0700
From: Doug Anderson <dianders@...omium.org>
To: Brigham Campbell <me@...ghamcampbell.com>
Cc: maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, 
	airlied@...il.com, simona@...ll.ch, linus.walleij@...aro.org, 
	neil.armstrong@...aro.org, jessica.zhang@....qualcomm.com, sam@...nborg.org, 
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] drm: Add MIPI support function and macros

Hi,

On Mon, Jul 28, 2025 at 10:44 PM Brigham Campbell
<me@...ghamcampbell.com> wrote:
>
> Create mipi_dsi_dcs_read_multi(), which accepts a mipi_dsi_multi_context
> struct for improved error handling and cleaner panel driver code.
>
> Create mipi_dsi_dcs_write_var_seq_multi() and
> mipi_dsi_generic_write_var_seq_multi() macros which allow MIPI panel
> drivers to write non-static data to display controllers.
>
> Signed-off-by: Brigham Campbell <me@...ghamcampbell.com>
> ---
>
> I looked into using __builtin_constant_p() to extend
> mipi_dsi_{generic,dcs}_write_seq_multi() to accept both static and
> non-static sequences of bytes and store them accordingly, it looked
> promising at first, but I found no such solution ultimately. At the very
> least, if we find a solution at some point, my hope is that cocinelle
> could be used to replace each of the new var_seq_multi() usages among
> drivers with an improved seq_multi().
>
>
>  drivers/gpu/drm/drm_mipi_dsi.c | 37 ++++++++++++++++++++++++++++++++++
>  include/drm/drm_mipi_dsi.h     | 35 ++++++++++++++++++++++++++++++++
>  2 files changed, 72 insertions(+)

nit: maybe make the subject a bit more specific, like:

drm: Add MIPI _multi reader func and two new write variants


> @@ -415,6 +417,22 @@ void mipi_dsi_dcs_set_tear_off_multi(struct mipi_dsi_multi_context *ctx);
>                 mipi_dsi_generic_write_multi(ctx, d, ARRAY_SIZE(d)); \
>         } while (0)
>
> +/**
> + * mipi_dsi_generic_write_var_seq_multi - transmit non-static data using a
> + * generic write packet

nit: "non-constant", not "non-static"

>From the caller's point of view the difference is that the data is
compile-time constant in one case and not compile-time constant in the
other case. It happens that means you can _store_ it in a "static
const" in one case and not in the other case, but that doesn't make
the parameters "static".


Other than nits:

Reviewed-by: Douglas Anderson <dianders@...omium.org>