From 8bc218410d6c2b22a7581fac6f3dc2ac1f8fc99f Mon Sep 17 00:00:00 2001 From: Raphael Assenat Date: Tue, 3 Oct 2006 01:15:03 -0700 Subject: [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 Signed-off-by: Antonino Daplas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/video/mbx/mbxfb.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/video/mbx/mbxfb.c b/drivers/video/mbx/mbxfb.c index 6849ab75d40..cfc6bf3615b 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) : -- cgit v1.2.3