linux-kernel - Re: [PATCH v4] drm/i2c: tda998x: fix sync generation and calculation

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Message-ID: <51C365E0.1060000@gmail.com>
Date:	Thu, 20 Jun 2013 22:28:16 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	David Airlie <airlied@...ux.ie>,
	Darren Etheridge <darren.etheridge@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] drm/i2c: tda998x: fix sync generation and calculation

On 06/20/2013 10:06 PM, Russell King - ARM Linux wrote:
> On Thu, Jun 20, 2013 at 09:46:03PM +0200, Sebastian Hesselbarth wrote:
>> +	ref_pix      = 3 + mode->hsync_start - mode->hdisplay;
>> +	de_pix_s     = mode->htotal - mode->hdisplay;
>> +	de_pix_e     = de_pix_s + mode->hdisplay;
>> +	hs_pix_s     = mode->hsync_start - mode->hdisplay;
>> +	hs_pix_e     = hs_pix_s + mode->hsync_end - mode->hsync_start;
>
> Correct, however, these can be simplified.
[...]
> These calculations are the same as what was originally in the driver:
>
> +       de_start   = mode->htotal - mode->hdisplay;
> +       de_end     = mode->htotal;
> +       hs_start   = mode->hsync_start - mode->hdisplay;
> +       hs_end     = mode->hsync_end - mode->hdisplay;
>
> when it was first committed.
>
> This is otherwise exactly what I came up with which gets my TV working
> again in HDMI mode.

Russell,

I am fine with any way to describe de/hs but you should notice that
I also modified refpix/refline and added interlaced sync. With the
original sync calculation, on some modes there was source blanking
captured by TDA998x which was also visible in the output image. I
chose the above description to make it more readable.

Also the patch takes care of input sync and output sync inversion
while the original driver always expected positive HS/VS.

I tested these sync settings on 4 DVI monitors and TV sets all
accepted each mode perfectly. Especially, not-so-cheap TV sets
are very picky about wrong sync.

Sebastian
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