[PATCH] mx3fb: Fix parameter to sdc_init_panel

On Thu, 10 Feb 2011, Alexander Stein wrote:

On Thursday 10 February 2011, 12:00:09 Guennadi Liakhovetski wrote:

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On Thu, 10 Feb 2011, Guennadi Liakhovetski wrote:

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On Thu, 10 Feb 2011, Alexander Stein wrote:

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h_end_width and v_end_width should only contain the front porches.
Otherwise, SCREEN_WIDTH (pixel clocks between HSYNC) in SDC_HOR_CONF
and SCREEN_HEIGHT (rows between VSYNC) in SDC_VER_CONF get false
values.

Hm, no, this corrupts image on my pcm990 test-board. What makes you think
this patch is needed? How do you see, that current values are "false?"

(I certainly meant the pcm037 module)

Ok, i will just write about HSYNC the problem about VSYNC is similar.
Let's assume we have a display with the following properties.
left_margin   = 38
right_margin  = 32
hsync_len     = 20
width         = 800

Without the patch we get the following arguments on sdc_init_panel
width           = 800
h_start_width   = 38 (left_margin)
h_sync_width    = 20 (hsync_len)
h_end_width     = 52 = 32 + 20 (right_margin + hsync_len)

So we will write into SDC_HOR_CONF:

reg = ((h_sync_width - 1) << 26) |
    ((width + h_start_width + h_end_width - 1) << 16);
reg = ((20 - 1) << 26) |
    ((800 + 38 + 52 - 1) << 16);

So the value SCREEN_WIDTH get written is
width + left_margin + right_margin + hsync_len
which is IMO wrong. The description in the reference manual states:

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Screen width minus 1. Specifies the number of pixel clock periods between
the last HSYNC and the new HSYNC.

It should just be: width + left_margin + right_margin
I fell accross it, as I have a display with 800 px width and rather big 
left_margin. The sum got greater than 1023 which is what SCREEN_WIDTH can hold 
at maximum.

I don't know which display you used, but I guess your right_margin (and 
lower_margin) needs to be adjusted.

Ok, agree. But then you need to adjust all current users and have them 
tested... Otherwise, of course, you can just adjust your platform panel 
data to work with the current calculations, even though in principle your 
patch seems to be doing the right thing (tm), according to the manual. But 
if applied as is without fixing all the users, it can very well break 
them...

Thanks
Guennadi

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Signed-off-by: Alexander Stein <redacted>
---

 drivers/video/mx3fb.c |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/video/mx3fb.c b/drivers/video/mx3fb.c
index ef71e56..9040833 100644
--- a/drivers/video/mx3fb.c
+++ b/drivers/video/mx3fb.c

@@ -881,12 +881,11 @@ static int __set_par(struct fb_info *fbi, bool

lock)

Also just occurred to me - your offset of 881 lines is 100 lines below my
offset for the same code - against what tree is this patch, or do you have
some local changes there? Can it be, that that's the reason for your
problem?

Oh, I didn't rebase this patch on current linux git. This patch is on my 
2.6.34 kernel. Anyway, since 2.6.34 there are no related patches on mx3fb.c.

Alexander

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Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/