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

[Maxime Ripard]

On Wed, Feb 23, 2022 at 03:38:20PM +0100, Marek Vasut wrote:
> On 2/23/22 15:37, Maxime Ripard wrote:
> > On Wed, Feb 23, 2022 at 03:09:08PM +0100, Marek Vasut wrote:
> > > On 2/23/22 14:47, Maxime Ripard wrote:
> > > > On Wed, Feb 23, 2022 at 02:45:30PM +0100, Marek Vasut 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).
> > > > 
> > > > panel-dpi is supposed to have two compatibles, the panel-specific one
> > > > and panel-dpi. This would obviously be tied to the panel-specific one.
> > > 
> > > This whole discussion is about the one which only has 'panel-dpi' compatible
> > > and describes the panel in DT completely. The specific compatible is not
> > > present in DT when this patch is needed.
> > 
> >  From the panel-dpi DT binding:
> > 
> > properties:
> >    compatible:
> >      description:
> >        Shall contain a panel specific compatible and "panel-dpi"
> >        in that order.
> >      items:
> >        - {}
> >        - const: panel-dpi
> > 
> > The panel-specific compatible is mandatory, whether you like it or not.
> 
> It doesn't seem to me that's the intended use per panel-simple.c , so maybe
> the bindings need to be fixed too ?

It's not clear to me why this has anything to do with panel-simple, but
the binding is correct, and that requirement is fairly standard. We have
the same thing with panel-lvds for example.

Maxime
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