linux-kernel - Re: [PATCH v2 4/7] imx-drm: ipuv3-crtc: Implement mode

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Message-ID: <20141222155303.GB32333@pengutronix.de>
Date:	Mon, 22 Dec 2014 16:53:03 +0100
From:	Philipp Zabel <pza@...gutronix.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Steve Longerbeam <slongerbeam@...il.com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, David Airlie <airlied@...ux.ie>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Denis Carikli <denis@...rea.com>,
	Jiada Wang <jiada_wang@...tor.com>,
	Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v2 4/7] imx-drm: ipuv3-crtc: Implement mode_fixup

Hi Russell,

On Sat, Dec 20, 2014 at 03:52:54PM +0000, Russell King - ARM Linux wrote:
> On Thu, Dec 18, 2014 at 06:00:23PM -0800, Steve Longerbeam wrote:
> > Ask the IPU display interface, via ipu_di_adjust_videomode(), to
> > adjust a video mode to meet any DI restrictions. The function takes
> > a subsystem independent videomode, so the drm_display_mode must be
> > converted to videomode first, and then the adjusted mode converted
> > back to a drm_display_mode.
> 
> What is the reason to use videomode (apart from it being subsystem
> independent)?  Do we forsee implementation of other output subsystems
> for the IPU?

There might be the issue of possible CSI -> IC -> DC -> DI passthrough,
where the DI timing must be synchronized to the CSI input signal.
I haven't really thought about how that should be integrated with the
DRM driver mostly because of the 1024 pixel output width maximum in the
IC, which limits the usefulness somewhat.
I like the use of struct videomode here for the symmetry with patch 6.
But currently, we could make ipu_di_adjust_videomode take a drm_display_mode
just as well.

regards
Philipp
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