linux-kernel - Re: [v8 4/6] drm/panel-simple: Update validation warnings for eDP panel description

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Message-ID: <YNnPqYjaZjmmrQTA@pendragon.ideasonboard.com>
Date:   Mon, 28 Jun 2021 16:33:29 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     rajeevny@...eaurora.org
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, thierry.reding@...il.com,
        sam@...nborg.org, robdclark@...il.com, dianders@...omium.org,
        lyude@...hat.com, jani.nikula@...el.com, robh@...nel.org,
        a.hajda@...sung.com, daniel.thompson@...aro.org,
        hoegsberg@...omium.org, abhinavk@...eaurora.org,
        seanpaul@...omium.org, kalyan_t@...eaurora.org,
        mkrishn@...eaurora.org
Subject: Re: [v8 4/6] drm/panel-simple: Update validation warnings for eDP
 panel description

Hi Rajeev,

On Mon, Jun 28, 2021 at 05:46:24PM +0530, rajeevny@...eaurora.org wrote:
> On 27-06-2021 23:48, Laurent Pinchart wrote:
> > On Sat, Jun 26, 2021 at 10:21:06PM +0530, Rajeev Nandan wrote:
> >> Do not give a warning for the eDP panels if the "bus_format" is
> >> not specified, since most eDP panels can support more than one
> >> bus formats and this can be auto-detected.
> >> Also, update the check to include bpc=10 for the eDP panel.
> >> 
> >> Signed-off-by: Rajeev Nandan <rajeevny@...eaurora.org>
> >> ---
> >> 
> >> Changes in v8:
> >> - New patch, to address the review comments of Sam Ravnborg [1]
> >> 
> >> [1] 
> >> https://lore.kernel.org/dri-devel/20210621184157.GB918146@ravnborg.org/
> >> 
> >>  drivers/gpu/drm/panel/panel-simple.c | 6 ++----
> >>  1 file changed, 2 insertions(+), 4 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/panel/panel-simple.c 
> >> b/drivers/gpu/drm/panel/panel-simple.c
> >> index 86e5a45..f966b562 100644
> >> --- a/drivers/gpu/drm/panel/panel-simple.c
> >> +++ b/drivers/gpu/drm/panel/panel-simple.c
> >> @@ -772,10 +772,8 @@ static int panel_simple_probe(struct device *dev, 
> >> const struct panel_desc *desc,
> >>  			desc->bpc != 8);
> >>  		break;
> >>  	case DRM_MODE_CONNECTOR_eDP:
> >> -		if (desc->bus_format == 0)
> >> -			dev_warn(dev, "Specify missing bus_format\n");
> >> -		if (desc->bpc != 6 && desc->bpc != 8)
> >> -			dev_warn(dev, "Expected bpc in {6,8} but got: %u\n", desc->bpc);
> >> +		if (desc->bpc != 6 && desc->bpc != 8 && desc->bpc != 10)
> >> +			dev_warn(dev, "Expected bpc in {6,8,10} but got: %u\n", desc->bpc);
> > 
> > You'll still get a warning is bpc == 0, is that intentional ?
> 
> This was not intentional, I missed considering bpc=0 case. As we are 
> removing the warning for bus_format=0 then a similar thing can be done 
> for the bpc=0 also. The bpc value should be a valid one if it is 
> specified. Unlike the bus_format, bpc has few possible values that can 
> be checked here along with 0. Please correct me if I misunderstood the 
> concept.
> I will fix this.

What's the point of specifying bpc if it's optional though ? Users of
the panel will need to support the case where bpc is set to 0. Have you
ensured that they all do ? Can they meaningfully use the bpc value if
they need to be ready to support bpc == 0 ?

-- 
Regards,

Laurent Pinchart