Re: [PATCH 1/2] drm/rockchip: dw_hdmi: relax mode_valid hook

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: dri-devel@lists.freedesktop.org,
	Michael Riesch <michael.riesch@wolfvision.net>,
	Sandy Huang <hjc@rock-chips.com>,
	kernel@pengutronix.de, linux-rockchip@lists.infradead.org
Subject: Re: [PATCH 1/2] drm/rockchip: dw_hdmi: relax mode_valid hook
Date: Thu, 25 Aug 2022 13:40:25 +0200	[thread overview]
Message-ID: <20220825114025.GR17485@pengutronix.de> (raw)
In-Reply-To: <a279a697-6960-c517-8984-335aa207126a@arm.com>

On Wed, Aug 24, 2022 at 05:07:50PM +0100, Robin Murphy wrote:
> On 2022-08-22 16:20, Sascha Hauer wrote:
> > The driver checks if the pixel clock of the given mode matches an entry
> > in the mpll config table. The frequencies in the mpll table are meant as
> > a frequency range up to which the entry works, not as a frequency that
> > must match the pixel clock. Return MODE_OK when the pixelclock is
> > smaller than one of the mpll frequencies to allow for more display
> > resolutions.
> 
> Has the issue been fixed that this table is also used to validate modes on
> RK3328, which doesn't even *have* the Synopsys phy? Last time I looked, that
> tended to lead to complete display breakage when the proper phy driver later
> decides it doesn't like a pixel clock that mode_valid already said was OK.
> 
> The more general concern is that these known-good clock rates are good, but
> others may not be even when nominally supported, which I suspect is the
> dirty secret of why it was implemented this way to begin with. I would
> really really love this patch so my RK3399 board can drive my 1920x1200
> monitor at native resolution, but on the other hand my RK3288 box generates
> such a crap 154MHz clock for that mode that - unless that's been improved in
> the meantime too - patch #2 might be almost be considered a regression if it
> means such a setup would start defaulting to an unusably glitchy display
> instead of falling back to 1920x1080 which does at least work perfectly
> (even if the slightly squished aspect ratio is ugly).

I could limit the change to rk3568 only. Would that be an option?
Not sure if I should rk3399 as well then as this would work, at least in
your setup.

Sascha

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