linux-kernel - Re: [PATCH 4/7] drm/vc4: dpi: Support RGB565 format

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Date:   Mon, 17 Oct 2022 18:12:44 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Maxime Ripard <maxime@...no.tech>,
        Maxime Ripard <mripard@...nel.org>,
        Eric Anholt <eric@...olt.net>, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, Rob Herring <robh@...nel.org>,
        Emma Anholt <emma@...olt.net>, dri-devel@...ts.freedesktop.org,
        Joerg Quinten <aBUGSworstnightmare@...il.com>,
        Chris Morgan <macromorgan@...mail.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] drm/vc4: dpi: Support RGB565 format

Hi Laurent

On Sat, 15 Oct 2022 at 18:29, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Maxime and Chris,
>
> Thank you for the patch.
>
> On Thu, Oct 13, 2022 at 11:56:48AM +0200, Maxime Ripard wrote:
> > From: Chris Morgan <macromorgan@...mail.com>
> >
> > The RGB565 format with padding over 24 bits
> > (MEDIA_BUS_FMT_RGB565_1X24_CPADHI) is supported by the vc4 DPI
> > controller as "mode 3".  This is what the Geekworm MZP280 DPI display
>
> The code below uses DPI_FORMAT_16BIT_565_RGB_2. Is that mode 3, or
> should the commit message refer to mode 2 ?

It's a mis-mash of documentation from the firmware stack.
[1] lists the firmware modes, which start at 1 for the equivalent of
DPI_FORMAT_9BIT_666_RGB, so there padded RGB565 is mode 3.

I'd advocate dropping the reference to which mode it is:
The RGB565 format with padding over 24 bits
(MEDIA_BUS_FMT_RGB565_1X24_CPADHI) is supported by the vc4 DPI controller.

  Dave

[1] https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#parallel-display-interface-dpi

> With this fixed,
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>
> > uses, so let's add support for it in the DPI controller driver.
> >
> > Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> > Signed-off-by: Chris Morgan <macromorgan@...mail.com>
> > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> > ---
> >  drivers/gpu/drm/vc4/vc4_dpi.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/vc4/vc4_dpi.c b/drivers/gpu/drm/vc4/vc4_dpi.c
> > index 1f8f44b7b5a5..7da3dd1db50e 100644
> > --- a/drivers/gpu/drm/vc4/vc4_dpi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_dpi.c
> > @@ -182,6 +182,10 @@ static void vc4_dpi_encoder_enable(struct drm_encoder *encoder)
> >                               dpi_c |= VC4_SET_FIELD(DPI_FORMAT_16BIT_565_RGB_3,
> >                                                      DPI_FORMAT);
> >                               break;
> > +                     case MEDIA_BUS_FMT_RGB565_1X24_CPADHI:
> > +                             dpi_c |= VC4_SET_FIELD(DPI_FORMAT_16BIT_565_RGB_2,
> > +                                                    DPI_FORMAT);
> > +                             break;
> >                       default:
> >                               DRM_ERROR("Unknown media bus format %d\n",
> >                                         bus_format);
> >
>
> --
> Regards,
>
> Laurent Pinchart