lxfb driver regression

Thu May 8 10:48:08 EDT 2008

On Thu, 08 May 2008 15:56:36 +0200
Jens Rottmann <JRottmann at LiPPERT-AT.de> wrote:

> Hi Andres,
> 
> > Without this patch, I get the following (correct) output from the
> > lxfb and console code:
> > [    0.939827] lxfb 0000:00:01.1: 16384 KB of video memory at
> > 0xfd000000 [    1.009194] Console: switching to colour frame buffer
> > device 150x56     
> 
> > Without it, the cols/width is screwy (and I get a blank white
> > screen): [   20.706836] lxfb 0000:00:01.1: 16384 KB of video memory
> > at 0xfd000000 [   20.788538] Console: switching to colour frame
> > buffer device 100x40          
> 
> I've searched all morning, but I don't get it. The only place the
> (changed) pll_table[] gets used is lx_set_clock(), and this doesn't
> return anything at all. lx_set_clock() gets told which dotclock to
> configure and it does its best to comply, but it doesn't report back,
> which clock it actually was able to select. So how on earth can
> changing this table cause fbcon or lxfb to decide for a completely
> different videomode?? Without the patch it seems to use the special
> 1200x900 OLPC DCON mode. With the patch it looks like it switches to
> some 800x640 mode. No idea where this mode might come from.

I played with it a bit last night. The pixclock that's specified is
17460 (from the olpc dcon table).  This gives a freq of 0xdfb9.
lx_set_clock then tries to figure out the best pll from the pll_table
by looking at the closest frequency.  Prior to your patch, this was:

  { 0x00004286, 56250 },
The freq difference was -1023, the closest of any in the table.   So,
we stuff 0x4286 into MSR_GLCP_DOTPLL, and all is good.

Your patch adds:
  { 0x00014170, 57375 },
The freq difference there is only 102, so lx_set_clock chooses
0x14170 as the pllval.

I'm unsure as to how that ends up causing the vc cols/rows stuff
to change..

> 
> And why does the lxfb init take place 20 sec later with the patch? Is
> there some initrd manually setting a different mode? Is this
> offending 800x640 mode maybe not coming from the kernel, but from
> some startup script via "fbset" and "/etc/fb.modes"?
> 

Nope, that's a separate bug; IDE hangs for 20 seconds and then times
out.  I believe it's a regression in rc1, but I haven't had the chance
to look at it yet.  There's no initrd being used in this kernel.

> I don't have an OLPC, so could you please run "fbset -i -v" with and
> without my patch. Hopefully this gives some clues...
> 
> I have also attached a cut down version of my patch. It still adds
> all the PLL settings for < 25 MHz dotclocks, but it no longer
> supplements the > 25 MHz clocks with intermediate steps. I'm only
> guessing here, I don't see what big difference this would make, but
> still ... could you please give it a try if you have time?
> 

I'm not sure if I'll be able to get to this today, but certainly by
tomorrow.  BTW, where did the intermediate values in your table come from?
The LX data book shows the DOTPLL equation (6.14.2.14), but very little
documentation of DIV4 or the usable values below 15MHz.

> Thanks a lot for your help.
> 
> Regards,
> Jens Rottmann
> 
> =============X8=================X8==============================
> lxfb: extend PLL table to support dotclocks below 25 MHz
> 
> Extends the PLL frequency table of the AMD Geode-LX frame buffer
> driver to make use of the DIV4 bit, thus adding support for
> dotclocks between 6 and 24 MHz.  These are needed for small LCDs
> (e.g. 320x240).
> 
> Signed-off-by: Jens Rottmann <JRottmann at LiPPERT-AT.de>
> ---
> 
> --- linux-2.6.25/drivers/video/geode/lxfb_ops.c
> +++ lxfb_clocks_added/drivers/video/geode/lxfb_ops.c
> @@ -34,35 +34,63 @@ static const struct {
>    unsigned int pllval;
>    unsigned int freq;
>  } pll_table[] = {
> -  { 0x000031AC, 24923 },
> -  { 0x0000215D, 25175 },
> -  { 0x00001087, 27000 },
> -  { 0x0000216C, 28322 },
> -  { 0x0000218D, 28560 },
> -  { 0x000010C9, 31200 },
> -  { 0x00003147, 31500 },
> -  { 0x000010A7, 33032 },
> -  { 0x00002159, 35112 },
> -  { 0x00004249, 35500 },
> -  { 0x00000057, 36000 },
> -  { 0x0000219A, 37889 },
> -  { 0x00002158, 39168 },
> -  { 0x00000045, 40000 },
> -  { 0x00000089, 43163 },
> -  { 0x000010E7, 44900 },
> -  { 0x00002136, 45720 },
> -  { 0x00003207, 49500 },
> -  { 0x00002187, 50000 },
> -  { 0x00004286, 56250 },
> -  { 0x000010E5, 60065 },
> -  { 0x00004214, 65000 },
> -  { 0x00001105, 68179 },
> -  { 0x000031E4, 74250 },
> -  { 0x00003183, 75000 },
> -  { 0x00004284, 78750 },
> -  { 0x00001104, 81600 },
> -  { 0x00006363, 94500 },
> -  { 0x00005303, 97520 },
> +  { 0x000131AC,   6231 },
> +  { 0x0001215D,   6294 },
> +  { 0x00011087,   6750 },
> +  { 0x0001216C,   7081 },
> +  { 0x0001218D,   7140 },
> +  { 0x000110C9,   7800 },
> +  { 0x00013147,   7875 },
> +  { 0x000110A7,   8258 },
> +  { 0x00012159,   8778 },
> +  { 0x00014249,   8875 },
> +  { 0x00010057,   9000 },
> +  { 0x0001219A,   9472 },
> +  { 0x00012158,   9792 },
> +  { 0x00010045,  10000 },
> +  { 0x00010089,  10791 },
> +  { 0x000110E7,  11225 },
> +  { 0x00012136,  11430 },
> +  { 0x00013207,  12375 },
> +  { 0x00012187,  12500 },
> +  { 0x00014286,  14063 },
> +  { 0x000110E5,  15016 },
> +  { 0x00014214,  16250 },
> +  { 0x00011105,  17045 },
> +  { 0x000131E4,  18563 },
> +  { 0x00013183,  18750 },
> +  { 0x00014284,  19688 },
> +  { 0x00011104,  20400 },
> +  { 0x00016363,  23625 },
> +  { 0x000031AC,  24923 },
> +  { 0x0000215D,  25175 },
> +  { 0x00001087,  27000 },
> +  { 0x0000216C,  28322 },
> +  { 0x0000218D,  28560 },
> +  { 0x000010C9,  31200 },
> +  { 0x00003147,  31500 },
> +  { 0x000010A7,  33032 },
> +  { 0x00002159,  35112 },
> +  { 0x00004249,  35500 },
> +  { 0x00000057,  36000 },
> +  { 0x0000219A,  37889 },
> +  { 0x00002158,  39168 },
> +  { 0x00000045,  40000 },
> +  { 0x00000089,  43163 },
> +  { 0x000010E7,  44900 },
> +  { 0x00002136,  45720 },
> +  { 0x00003207,  49500 },
> +  { 0x00002187,  50000 },
> +  { 0x00004286,  56250 },
> +  { 0x000010E5,  60065 },
> +  { 0x00004214,  65000 },
> +  { 0x00001105,  68179 },
> +  { 0x000031E4,  74250 },
> +  { 0x00003183,  75000 },
> +  { 0x00004284,  78750 },
> +  { 0x00001104,  81600 },
> +  { 0x00006363,  94500 },
> +  { 0x00005303,  97520 },
>    { 0x00002183, 100187 },
>    { 0x00002122, 101420 },
>    { 0x00001081, 108000 },
> @@ -137,7 +165,7 @@ static void lx_set_clock(struct fb_info
>  	unsigned int diff, min, best = 0;
>  	unsigned int freq, i;
> 
> -	freq = (unsigned int) (0x3b9aca00 / info->var.pixclock);
> +	freq = (unsigned int) (1000000000 / info->var.pixclock);
> 
>  	min = abs(pll_table[0].freq - freq);
> 
> @@ -149,7 +177,7 @@ static void lx_set_clock(struct fb_info
>  		}
>  	}
> 
> -	lx_set_dotpll(pll_table[best].pllval & 0x7FFF);
> +	lx_set_dotpll(pll_table[best].pllval & 0x00017FFF);
>  }
> 
>  static void lx_graphics_disable(struct fb_info *info)
> 