diff options
| author | Raphael Assenat <raph@8d.com> | 2006-10-03 01:15:03 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-10-03 08:04:12 -0700 |
| commit | 8bc218410d6c2b22a7581fac6f3dc2ac1f8fc99f (patch) | |
| tree | e4b0ef3693052742df0233ab9c3a706382307ee3 /drivers | |
| parent | 9c5b39e0bcb407a95716de4650a2d1e6064baffa (diff) | |
[PATCH] mbxfb: Fix a chip bug? resulting in wrong pixclock
This is a workaround for what I think is a bug in the 2700G chip.
The PLL output frequency is adustable using 3 values (M, N and P. See code
for formula). The N value range is documented to be 1 to 7 but when it is set
to 1, the output frequency is lower than it should be (divided by 2), giving
unexpected results such as no sync on a CRT display.
This patch prevents N=1 when searching for the best value for the requested
pixclock.
Signed-off-by: Raphael Assenat <raph@8d.com>
Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/video/mbx/mbxfb.c | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/drivers/video/mbx/mbxfb.c b/drivers/video/mbx/mbxfb.c index 6849ab75d403..cfc6bf3615b5 100644 --- a/drivers/video/mbx/mbxfb.c +++ b/drivers/video/mbx/mbxfb.c @@ -118,8 +118,19 @@ static unsigned int mbxfb_get_pixclock(unsigned int pixclock_ps, /* convert pixclock to KHz */ pixclock = PICOS2KHZ(pixclock_ps); + /* PLL output freq = (ref_clk * M) / (N * 2^P) + * + * M: 1 to 63 + * N: 1 to 7 + * P: 0 to 7 + */ + + /* RAPH: When N==1, the resulting pixel clock appears to + * get divided by 2. Preventing N=1 by starting the following + * loop at 2 prevents this. Is this a bug with my chip + * revision or something I dont understand? */ for (m = 1; m < 64; m++) { - for (n = 1; n < 8; n++) { + for (n = 2; n < 8; n++) { for (p = 0; p < 8; p++) { clk = (ref_clk * m) / (n * (1 << p)); err = (clk > pixclock) ? (clk - pixclock) : |