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

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Date:   Wed, 5 Apr 2023 17:03:26 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Roman Beranek <romanberanek@...oud.com>
Cc:     Frank Oltmanns <frank@...manns.dev>, 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

On Wed, Apr 05, 2023 at 02:34:11PM +0200, Roman Beranek wrote:
> Hello Maxime,
> 
> On Wed Mar 29, 2023 at 9:58 PM CEST, Maxime Ripard wrote:
> > > In order to preserve semantic correctness however, I propose to preface
> > > the change with a patch that renames sun4i_dotclock and tcon-pixel-clock
> > > such that dot/pixel is replaced with d/data. What do you think?
> >
> > I don't think it's exposed to the userspace in any way so it makes sense to me
> >
> 
> Here's a new series that includes those renames:
> <https://lore.kernel.org/all/20230331110245.43527-1-me@crly.cz/>
> 
> It turns out however that the new dclk rates can't be set exactly as
> requested without touching pll-video0*, tcon0 now therefore gets
> reparented from pll-mipi to pll-video0-2x which, as it further turns
> out, breaks DSI. While simply forbidding the video0-2x mux option seems
> to me as the right way to go because there's not much use for it with
> non-DSI interfaces either besides the opportunity to power pll-mipi
> down, I'd like to run by you first.

Sounds reasonable

> * As pll-mipi doesn't have CLK_SET_RATE_PARENT flag set, pll-video0
>   retains its boot-time rate of 294 MHz set by sunxi-dw-hdmi driver
>   in u-boot. Why 294 MHz (as opposed to the default rate of 297 MHz)?
>   The driver actually asks for 297 MHz, clock_set_pll3 rounds it to
>   294 MHz though because it limits itself to 6 MHz steps.

We could also address that though

Maxime

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