Re: [PATCH v2 3/3] drm/panel-simple: allow LVDS format override

[Johannes Zink]

Hi Laurent,

thanks for your review and your feedback.

On 6/2/23 17:39, Laurent Pinchart wrote:
> Hi Johannes,
>
> Thank you for the patch.
>
> On Tue, May 23, 2023 at 10:19:43AM +0200, Johannes Zink wrote:
> > Some panels support multiple LVDS data mapping formats, which can be
> > used e.g. run displays on jeida-18 format when only 3 LVDS lanes are
> > available.
> >
> > Add parsing of an optional data-mapping devicetree property, which also
> > touches up the bits per color to match the bus format.
>
> Of course one could argue that the innolux,g101ice-l01 panel should have
> used the panel-lvds bindings... :-)

I would prefer to add it in the panel-simple, if ever possible, as this already 
has the timing information etc. in the driver. I would probably opt to use the 
panel-lvds for an entirely new LVDS display, but as the innolux,g101ice-l01 is 
already supported in panel-simple, imho there should be no harm in supporting 
the jeida-18 operating mode as well. Also other displays in panel-simple 
_might_ benefit from supporting non-default LVDS mapping modes, though I have 
not researched whether they have actual hardware support for doing so.

> > Signed-off-by: Johannes Zink <j.zink@xxxxxxxxxxxxxx>
> >
> > ---
> >
> > Changes:
> >
> >    v1 -> v2: - fix missing unwind goto found by test robot
> >                Reported-by: kernel test robot <lkp@xxxxxxxxx>
> >                Reported-by: Dan Carpenter <error27@xxxxxxxxx>
> >                Link: https://lore.kernel.org/r/202304160359.4LHmFOlU-lkp@xxxxxxxxx/
> > ---
> >   drivers/gpu/drm/panel/panel-simple.c | 39 +++++++++++++++++++++++++++++++++++-
> >   1 file changed, 38 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> > index 2a9c1a785a5c..0a35fdb49ccb 100644
> > --- a/drivers/gpu/drm/panel/panel-simple.c
> > +++ b/drivers/gpu/drm/panel/panel-simple.c
> > @@ -40,6 +40,7 @@
> >   #include <drm/drm_edid.h>
> >   #include <drm/drm_mipi_dsi.h>
> >   #include <drm/drm_panel.h>
> > +#include <drm/drm_of.h>
> >   
> >   /**
> >    * struct panel_desc - Describes a simple panel.
> > @@ -559,7 +560,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
> >   	struct device_node *ddc;
> >   	int connector_type;
> >   	u32 bus_flags;
> > -	int err;
> > +	int err, ret;
> >   
> >   	panel = devm_kzalloc(dev, sizeof(*panel), GFP_KERNEL);
> >   	if (!panel)
> > @@ -605,6 +606,42 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
> >   			panel_simple_parse_panel_timing_node(dev, panel, &dt);
> >   	}
> >   
> > +
>
> Double blank line.

ack, gonna fix in v3.

> > +	/* optional data-mapping property for overriding bus format */
>
> s/optional/Optional/

ack, gonna fix in v3.

> > +	ret = drm_of_lvds_get_data_mapping(dev->of_node);
> > +	if (ret == -EINVAL) {
> > +		dev_warn(dev, "Ignore invalid data-mapping property");
> > +	} else if (ret != -ENODEV) {
>
> If someone incorrectly sets the property in DT for a non-LVDS panel,
> the result won't be nice. That's of course a DT issue, but I wonder if
> we could/should protect against it. You could move this code to a
> separate function (which would have the added benefit of lowering the
> indentation level as you can return early in error cases), and call it
> from panel_simple_probe() only if the panel is an LVDS panel (as
> reported by its desc->bus_format value).

that's a good idea, gonna change it for v3.

> > +		int bpc;
> > +
> > +		switch (ret) {
> > +		default:
> > +			WARN_ON(1);
> > +			fallthrough;
> > +		case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
> > +			fallthrough;
> > +		case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
> > +			bpc = 8;
> > +			break;
> > +		case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
> > +			bpc = 6;
> > +		}
> > +
> > +		if (desc->bpc != bpc || desc->bus_format != ret) {
> > +			struct panel_desc *override_desc;
> > +
> > +			override_desc = devm_kmemdup(dev, desc, sizeof(*desc), GFP_KERNEL);
> > +			if (!override_desc) {
> > +				err = -ENOMEM;
> > +				goto free_ddc;
> > +			}
> > +
> > +			override_desc->bus_format = ret;
> > +			override_desc->bpc = bpc;
> > +			panel->desc = override_desc;
> > +		}
> > +	}
> > +
> >   	connector_type = desc->connector_type;
> >   	/* Catch common mistakes for panels. */
> >   	switch (connector_type) {

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