Re: [PATCH] drm/panel: panel-simple: validate panel description

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sam,

On Sun, Jul 12, 2020 at 12:58:19PM +0200, Sam Ravnborg wrote:
> On Sun, Jul 12, 2020 at 01:56:16AM +0300, Laurent Pinchart wrote:
> > Hi Sam,
> > 
> > (CC'ing Daniel)
> > 
> > Thank you for the patch.
> > 
> > On Sat, Jul 11, 2020 at 11:47:26AM +0200, Sam Ravnborg wrote:
> > > Warn is we detect a panel with missing descriptions.
> > 
> > s/is/if/
> > 
> > > This is inpsired by a similar patch by Laurent that introduced checks
> > > for LVDS panels - this extends the checks to the reminaing type of
> > 
> > s/reminaing type/remaining types/
> > 
> > > connectors.
> > > 
> > > This is known to fail for some of the existing panels but added
> > > despite this as we need help from people using the panels to
> > > add the missing info.
> > > The checks are not complete but will catch the most common mistakes.
> > > The checks at the same time serves as documentation for the minimum
> > > required description for a panel.
> > > 
> > > Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
> > > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > Cc: Thierry Reding <thierry.reding@gmail.com>
> > > Cc: Sam Ravnborg <sam@ravnborg.org>
> > > ---
> > > 
> > > This is my attempt on the validation described in the previous mail.
> > > The assignment of default connector_type will then be a follow-up patch
> > > to this.
> > > 
> > > 	Sam
> > > 
> > >  drivers/gpu/drm/panel/panel-simple.c | 32 ++++++++++++++++++++++++++--
> > >  1 file changed, 30 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> > > index 2aff93accad5..025a7ccdfcb3 100644
> > > --- a/drivers/gpu/drm/panel/panel-simple.c
> > > +++ b/drivers/gpu/drm/panel/panel-simple.c
> > > @@ -549,8 +549,12 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
> > >  			panel_simple_parse_panel_timing_node(dev, panel, &dt);
> > >  	}
> > >  
> > > -	if (desc->connector_type == DRM_MODE_CONNECTOR_LVDS) {
> > > -		/* Catch common mistakes for LVDS panels. */
> > > +	/* Catch common mistakes for panels. */
> > > +	switch (desc->connector_type) {
> > > +	case 0:
> > > +		WARN(desc->connector_type == 0, "specify missing connector_type\n");
> > > +		break;
> > > +	case DRM_MODE_CONNECTOR_LVDS:
> > >  		WARN_ON(desc->bus_flags &
> > >  			~(DRM_BUS_FLAG_DE_LOW |
> > >  			  DRM_BUS_FLAG_DE_HIGH |
> > > @@ -564,6 +568,30 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
> > >  		WARN_ON((desc->bus_format == MEDIA_BUS_FMT_RGB888_1X7X4_SPWG ||
> > >  			 desc->bus_format == MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA) &&
> > >  			desc->bpc != 8);
> > > +		break;
> > > +	case DRM_MODE_CONNECTOR_eDP:
> > > +		WARN_ON(desc->bus_format == 0);
> > > +		WARN_ON(desc->bpc != 6 && desc->bpc != 8);
> > > +		break;
> > > +	case DRM_MODE_CONNECTOR_DSI:
> > > +		WARN_ON(desc->bpc != 6 && desc->bpc != 8);
> > > +		break;
> > > +	case DRM_MODE_CONNECTOR_DPI:
> > > +		WARN_ON(desc->bus_flags &
> > > +			~(DRM_BUS_FLAG_DE_LOW |
> > > +			  DRM_BUS_FLAG_DE_HIGH |
> > > +			  DRM_BUS_FLAG_PIXDATA_SAMPLE_POSEDGE |
> > > +			  DRM_BUS_FLAG_PIXDATA_SAMPLE_NEGEDGE |
> > > +			  DRM_BUS_FLAG_DATA_MSB_TO_LSB |
> > > +			  DRM_BUS_FLAG_DATA_LSB_TO_MSB |
> > > +			  DRM_BUS_FLAG_SYNC_SAMPLE_POSEDGE |
> > > +			  DRM_BUS_FLAG_SYNC_SAMPLE_NEGEDGE));
> > > +		WARN_ON(desc->bus_format == 0);
> > > +		WARN_ON(desc->bpc != 6 && desc->bpc != 8);
> > > +		break;
> > > +	default:
> > > +		WARN(true, "panel has unknown connector_type: %d\n", desc->connector_type);
> > > +		break;
> > >  	}
> > 
> > The checks look sane to me. For LVDS we've added the WARN_ON after
> > checking all LVDS panels [1], so the warning will only get displayed for
> > new panel drivers. For other types of panel, this will cause lots of
> > WARN_ON to trigger. On one hand it gets the issues noticed, which should
> > help fixing them, but on the other hand it will also scare lots of users
> > and developers. I'm not sure if we should downgrade that to a dev_warn()
> > for some time until we get at least the majority of the issues fixed.
> > Daniel, any opinion ?
> 
> We should be noisy, but not too noisy.
> dev_warn() is fine, maybe only dev_info()?
> 
> Unless I get other feedback I will convert to dev_info() in the
> next version of the patch.
> Fixing all panels before we add the checks, is not feasible.
> Access to datasheet is not easy/possible for many panels.

And that's the whole point of adding the warning, trying to get the
people who have access to the panels to help fixing the problem.

I think a dev_warn() would be a good compromise, the missing info can
have adverse consequences, so a warning seems appropriate.

> > [1] Actually not quite, I've just sent "[PATCH] drm: panel: simple: Fix
> > bpc for LG LB070WV8 panel" to fix one bpc issue.
> > 
> > >  	drm_panel_init(&panel->base, dev, &panel_simple_funcs,

-- 
Regards,

Laurent Pinchart
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