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

From: Sebastian Hesselbarth
Date: Thu Jun 20 2013 - 16:28:28 EST

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.


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.

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