[RFC PATCH] drm/panel: simple: panel-dpi: use bus-format to set bpc and bus_format

[Max Krummenacher]

The goal here is to set the element bus_format in the struct
panel_desc. This is an enum with the possible values defined in
include/uapi/linux/media-bus-format.h.

The enum values are not constructed in a way that you could calculate
the value from color channel width/shift/mapping/whatever. You rather
would have to check if the combination of color channel
width/shift/mapping/whatever maps to an existing value and otherwise
EINVAL out.

I don't see the value in having yet another way of how this
information can be specified and then having to write a more
complicated parser which maps the dt data to bus_format.

On Wed, Feb 23, 2022 at 2:45 PM Marek Vasut <marex at denx.de> wrote:
>
> On 2/23/22 14:41, Maxime Ripard wrote:
> > Hi,
> >
> > On Tue, Feb 22, 2022 at 09:47:23AM +0100, Max Krummenacher wrote:
> >> Use the new property bus-format to set the enum bus_format and bpc.
> >> Completes: commit 4a1d0dbc8332 ("drm/panel: simple: add panel-dpi support")
> >>
> >> Signed-off-by: Max Krummenacher <max.krummenacher at toradex.com>
> >>
> >> ---
> >>
> >>   drivers/gpu/drm/panel/panel-simple.c | 32 ++++++++++++++++++++++++++++
> >>   1 file changed, 32 insertions(+)
> >>
> >> Relates to the discussion: https://lore.kernel.org/all/20220201110717.3585-1-cniedermaier@dh-electronics.com/
> >>
> >> Max
> >>
> >> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> >> index c5f133667a2d..5c07260de71c 100644
> >> --- a/drivers/gpu/drm/panel/panel-simple.c
> >> +++ b/drivers/gpu/drm/panel/panel-simple.c
> >> @@ -453,6 +453,7 @@ static int panel_dpi_probe(struct device *dev,
> >>      struct panel_desc *desc;
> >>      unsigned int bus_flags;
> >>      struct videomode vm;
> >> +    const char *format = "";
> >>      int ret;
> >>
> >>      np = dev->of_node;
> >> @@ -477,6 +478,37 @@ static int panel_dpi_probe(struct device *dev,
> >>      of_property_read_u32(np, "width-mm", &desc->size.width);
> >>      of_property_read_u32(np, "height-mm", &desc->size.height);
> >>
> >> +    of_property_read_string(np, "bus-format", &format);
> >> +    if (!strcmp(format, "BGR888_1X24")) {
> >> +            desc->bpc = 8;
> >> +            desc->bus_format = MEDIA_BUS_FMT_BGR888_1X24;
> >> +    } else if (!strcmp(format, "GBR888_1X24")) {
> >> +            desc->bpc = 8;
> >> +            desc->bus_format = MEDIA_BUS_FMT_GBR888_1X24;
> >> +    } else if (!strcmp(format, "RBG888_1X24")) {
> >> +            desc->bpc = 8;
> >> +            desc->bus_format = MEDIA_BUS_FMT_RBG888_1X24;
> >> +    } else if (!strcmp(format, "RGB444_1X12")) {
> >> +            desc->bpc = 6;
> >> +            desc->bus_format = MEDIA_BUS_FMT_RGB444_1X12;
> >> +    } else if (!strcmp(format, "RGB565_1X16")) {
> >> +            desc->bpc = 6;
> >> +            desc->bus_format = MEDIA_BUS_FMT_RGB565_1X16;
> >> +    } else if (!strcmp(format, "RGB666_1X18")) {
> >> +            desc->bpc = 6;
> >> +            desc->bus_format = MEDIA_BUS_FMT_RGB666_1X18;
> >> +    } else if (!strcmp(format, "RGB666_1X24_CPADHI")) {
> >> +            desc->bpc = 6;
> >> +            desc->bus_format = MEDIA_BUS_FMT_RGB666_1X24_CPADHI;
> >> +    } else if (!strcmp(format, "RGB888_1X24")) {
> >> +            desc->bpc = 8;
> >> +            desc->bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> >> +    } else {
> >> +            dev_err(dev, "%pOF: missing or unknown bus-format property\n",
> >> +                    np);
> >> +            return -EINVAL;
> >> +    }
> >> +
> >
> > It doesn't seem right, really. We can't the bus format / bpc be inferred
> > from the compatible? I'd expect two panels that don't have the same bus
> > format to not be claimed as compatible.
>
> Which compatible ?
>
> Note that this is for panel-dpi compatible, i.e. the panel which has
> timings specified in DT (and needs bus format specified there too).
>
> I agree this doesn't look right however, some more generic color channel
> width/shift/mapping might be better.