Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK_REG

From: Maxime Ripard <maxime@cerno.tech>
To: Roman Beranek <romanberanek@icloud.com>
Cc: Frank Oltmanns <frank@oltmanns.dev>, Chen-Yu Tsai <wens@csie.org>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Samuel Holland <samuel@sholland.org>,
	dri-devel@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK_REG
Date: Wed, 29 Mar 2023 21:58:02 +0200	[thread overview]
Message-ID: <20230329195802.veybo3367zifw77n@penduick> (raw)
In-Reply-To: <CRHKFX934UA0.1MCKCD8SJSPIE@iMac.local>

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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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