Re: [linux-sunxi] Re: [PATCH RESEND v2 06/12] drm/sun4i: rgb: Add 1% tolerance to dclk frequency check when bridge is connected

From: Thierry Reding <thierry.reding@gmail.com>
To: Maxime Ripard <maxime.ripard@bootlin.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	devicetree <devicetree@vger.kernel.org>,
	David Airlie <airlied@linux.ie>, Chen-Yu Tsai <wens@csie.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Vasily Khoruzhick <anarsoul@gmail.com>,
	linux-sunxi <linux-sunxi@googlegroups.com>,
	Rob Herring <robh+dt@kernel.org>,
	Sean Paul <seanpaul@chromium.org>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	arm-linux <linux-arm-kernel@lists.infradead.org>,
	Icenowy Zheng <icenowy@aosc.io>
Subject: Re: [linux-sunxi] Re: [PATCH RESEND v2 06/12] drm/sun4i: rgb: Add 1% tolerance to dclk frequency check when bridge is connected
Date: Wed, 6 Feb 2019 12:42:33 +0100	[thread overview]
Message-ID: <20190206114233.GB21676@ulmo> (raw)
In-Reply-To: <20190206091608.yvws7iyjuhw3xsdk@flea>

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On Wed, Feb 06, 2019 at 10:16:08AM +0100, Maxime Ripard wrote:
> On Tue, Feb 05, 2019 at 09:49:17AM -0800, Vasily Khoruzhick wrote:
> > On Tue, Feb 5, 2019 at 7:42 AM Maxime Ripard <maxime.ripard@bootlin.com> wrote:
> > >
> > > On Mon, Feb 04, 2019 at 10:50:17AM -0800, Vasily Khoruzhick wrote:
> > > > On Mon, Feb 4, 2019 at 8:29 AM Icenowy Zheng <icenowy@aosc.io> wrote:
> > > > > >> IIRC, from the previous discussion, HDMI had a tolerancy requirement
> > > > > >> in the standard. Do you know if there's such a thing for eDP? That
> > > > > >> would solve the issue for all the eDP displays at once.
> > > > > >
> > > > > >I don't have access to eDP standard - vesa.org says it's available to
> > > > > >members only.
> > > > >
> > > > > Try out to grab an old version?
> > > > >
> > > > > I remember 1.0 is open.
> > > >
> > > > I can't find anything regarding dot clock tolerance in DisplayPort
> > > > specification.
> > >
> > > I guess since the DP is a VESA spec, it's probably .5%, just like on
> > > the EDID (well, CVT).
> > 
> > Unfortunately that's not enough for Pinebook. It needs 1% for 768p
> > panel.
> 
> And that mode is stored in the EDID as a standard (or established)
> timing, or a detailed timing?
> 
> If the latter, then it should also provide the tolerancies as part of
> the panel timing description.

The simple-panel driver can, in addition to a struct drm_display_mode
take a struct display_timings to specify the modes. These allow to
define <minimum, typical, maximum> triplets for each parameter, which
are usually found in panel datasheets.

Of course that's not going to help you much if all you have is EDID and
if that doesn't provide tolerances.

Thierry

> If the former, then what would be the advertised pixel clock and the
> one we can compute? Maybe we have a bug somewhere.
> 
> Maxime
> 
> -- 
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com

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