linux-kernel - Re: [PATCH RFC] drm/sun4i: rgb: Add 5% tolerance to dot clock frequency check

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Message-ID: <20161209093657.jcalemg5xpumr2ma@lukather>
Date:   Fri, 9 Dec 2016 10:36:57 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sean Paul <seanpaul@...omium.org>,
        Eric Anholt <eric@...olt.net>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH RFC] drm/sun4i: rgb: Add 5% tolerance to dot clock
 frequency check

On Wed, Dec 07, 2016 at 10:26:25AM +0800, Chen-Yu Tsai wrote:
> > Some panels require an exact frequency, some have a minimal frequency
> > but no maximum, some have a maximum frequency but no minimal, and I
> > guess most of them deviates by how much exactly they can take (and
> > possibly can take more easily a higher frequency, but are less
> > tolerant if you take a frequency lower than the nominal.
> >
> > And we cannot remove that check entirely, since some bridges will
> > report out of range frequencies for higher modes that we know we
> > cannot reach.
> 
> I believe this should be handled by the bridge driver in the check
> callback?

This doesn't really have anything to do with the bridge itself, it's a
limitation on the encoder. For all we know, the bridge might be able
to operate at the higher resolutions without any issues if the encoder
was able to.

> The callback I'm changing is attached to the connector, which I
> think doesn't get used if you have a bridge instead.  And this only
> checks the pre-registered display modes, such as those specified in
> simple-panel or EDID.

Geeee, I forgot to send that one (and thought I did)... I'll send that
patch next week, but basically, I was creating a mode_valid hook at
the encoder level, and moving the RGB mode_valid hook from the
connector to the encoder (since it really is an encoder limitation).

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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