linux-kernel - Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity

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Date:	Thu, 26 Nov 2015 15:20:51 +0100
From:	Manfred Schlaegl <manfred.schlaegl@....at>
To:	Philipp Zabel <p.zabel@...gutronix.de>
CC:	David Airlie <airlied@...ux.ie>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org,
	Manfred Schlaegl <manfred.schlaegl@...zinger.com>,
	Steve Longerbeam <slongerbeam@...il.com>,
	Deepak Das <deepak_das@...tor.com>,
	Jiada Wang <jiada_wang@...tor.com>, linux-fbdev@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] drm: add support for for clk and de polarity

On 2015-11-25 18:22, Philipp Zabel wrote:
> Am Mittwoch, den 15.07.2015, 17:50 +0200 schrieb Manfred Schlaegl:
>> To get full support for parallel and LVDS displays with drm:
>> Add representation for clock and data enable polarity in drm_display_mode
>> flags (similar to HSYNC/VSYNC polarity) and update conversion functions
>> from/to videomode accordingly.
>>
>> This is especially important for embedded devices where parallel(RGB) and
>> LVDS displays are still widely used and drm already plays an important
>> role.
>>
>> Tested on Freescale i.MX53(parallel) and i.MX6(LVDS).
>>
>> Background:
>> There was the ability to set polarity of clock and data enable signals
>> in devicetree(display-timing), struct display_timing and struct videomode,
>> but there was no representation for this in struct drm_display_mode.
>> Example on Freescale i.MX53/i.MX6 SoC's:
>>  * A parallel display using different clock polarity is set up using
>>    display-timing in devicetree
>>  * ipuv3 parallel outputs clock with wrong polarity
>>
>> Signed-off-by: Manfred Schlaegl <manfred.schlaegl@....at>
> 
> Any comments on whether data enable and pixel clock polarity flags can
> be added to the visible DRM_MODE_FLAGs, and if not, where else this
> information should be kept? struct drm_display_info?
> 
> This patch and the following IPUv3 patch are useful and necessary for
> quite some panels connected to i.MX SoCs, but adding DRM_MODE_FLAGs is
> somewhat out of my jurisdiction.
> 
> best regards
> Philipp
> 

Good to see that this discussion is triggered.

State of the sent patches respective to git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git (78c4a49)
 * [RFC PATCH 1/2] drm: add support for for clk and de polarity
   * applies unmodified
 * [RFC PATCH 2/2] gpu: ipu-v3: use clock and de polarity from videomode
   * does not apply -> but this can be fixed with corrections of line offsets (using patch)
>From a code review I think the modifications must work, but I did no testing on kernel versions newer than 4.1.13.
On demand, I can redo tests on some of our i.MX53 (parallel) and i.MX6 (lvds) boards and send actual patches.

best regards,
Manfred

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