linux-kernel - Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK

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Message-Id: <CRC7SQGZJDK0.3FEG3RZR6IR5U@iMac.local>
Date:   Tue, 21 Mar 2023 17:50:43 +0100
From:   "Roman Beranek" <romanberanek@...oud.com>
To:     "Maxime Ripard" <maxime@...no.tech>
Cc:     "Chen-Yu Tsai" <wens@...e.org>, "David Airlie" <airlied@...il.com>,
        "Daniel Vetter" <daniel@...ll.ch>,
        "Jernej Skrabec" <jernej.skrabec@...il.com>,
        "Samuel Holland" <samuel@...lland.org>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-sunxi@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from
 TCON0_DCLK_REG

Hello Maxime,

On Tue Mar 21, 2023 at 3:56 PM CET, Maxime Ripard wrote:
>
> This is similar to
> https://lore.kernel.org/all/20230319160704.9858-2-frank@oltmanns.dev/
>
> What's the story there?

Yes, Frank Oltmanns wrote me recently in relation to a patch I wrote
~ 3 years ago that addressed the framerate issue, proposing to
collaborate on pushing it upstream, however as I've been keeping up
with my inbox rather sporadically these days, by the time I read his
message, Frank had already taken the initiative and sent the patch.
So that's how we've got to this slightly awkward situation with two
patches on the same subject arriving 1 day apart of each other.

The problem with the original patch was that it went around
sun4i_dotclock by feeding it a rate adjusted such that the pll-mipi rate
was set correctly. I couldn't quite figure out at the time of how big
a portion of the tcon logic does the sun4i_dotclock code need to be made
aware of.

>Also, how was it tested/confirmed?

By counting Vblank interrupts (GIC 118).

Roman