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

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Message-Id: <CRHKFX934UA0.1MCKCD8SJSPIE@iMac.local>
Date:   Tue, 28 Mar 2023 01:48:33 +0200
From:   "Roman Beranek" <romanberanek@...oud.com>
To:     "Maxime Ripard" <maxime@...no.tech>,
        "Frank Oltmanns" <frank@...manns.dev>
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

On Mon Mar 27, 2023 at 10:20 PM CEST, Maxime Ripard wrote:
>
> On Sat, Mar 25, 2023 at 12:40:04PM +0100, Frank Oltmanns wrote:
> > Claiming to set the divider to a different value (bpp / lanes) than what we’re actually using in
> > the end (SUN6I_DSIO_TCON_DIV) is somehow bugging me. I feel like the proposal that I submitted is
> > more direct: <https://lore.kernel.org/all/20230319160704.9858-2-frank@oltmanns.dev/>
>
> Yeah, this patch looks better to me too: it's simpler, more straightforward. If Roman can confirm it
> works with his testing, I'll be happy to merge it.
>

So I've just found out that my understanding of what sun4i_dotclock is
was wrong the whole time. I treated it as a virtual clock representing
the true CRTC pixel clock and only coincidentally also matching what
A64 Reference Manual labels as TCON0 data clock (a coincidence to which
DSI is an exception).

Now that I finally see dotclock as 'what could dclk be an abbreviation
to', I to agree that it's not only straightforward but also correct to
keep the divider at 4 and adjust the rate as is done it the patch Frank
submitted.

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?

Roman