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

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Message-ID: <20230329195802.veybo3367zifw77n@penduick>
Date:   Wed, 29 Mar 2023 21:58:02 +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 Tue, Mar 28, 2023 at 01:48:33AM +0200, Roman Beranek wrote:
> 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?

I don't think it's exposed to the userspace in any way so it makes sense to me

Maxime

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