Re: [PATCH] atyfb: Replace busy loop with mdelay()
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2007-03-05 23:54:58
Subsystem:
framebuffer layer, the rest · Maintainers:
Helge Deller, Linus Torvalds
On Thu, 22 Feb 2007 02:20:33 +0200 Ville Syrj__l__ [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Replace a busy loop with mdelay() in atyfb clock setup code. This fixes boot hangs several people have experienced. Signed-off-by: Ville Syrjala <syrjala@sci.fi> --- This patch was already forwareded by James to some of you, but here it is with the proper changelog, signed-off-by line, and a language fix in the comment part. Also Cc:d stable@kernel.org as this seems like -stable material to me. drivers/video/aty/mach64_ct.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) Index: linux-2.6.20.1/drivers/video/aty/mach64_ct.c ===================================================================--- linux-2.6.20.1.orig/drivers/video/aty/mach64_ct.c +++ linux-2.6.20.1/drivers/video/aty/mach64_ct.c@@ -598,7 +598,6 @@ static void aty_resume_pll_ct(const stru struct atyfb_par *par = info->par; if (par->mclk_per != par->xclk_per) { - int i; /* * This disables the sclk, crashes the computer as reported: * aty_st_pll_ct(SPLL_CNTL2, 3, info);@@ -609,12 +608,10 @@ static void aty_resume_pll_ct(const stru aty_st_pll_ct(SCLK_FB_DIV, pll->ct.sclk_fb_div, par); aty_st_pll_ct(SPLL_CNTL2, pll->ct.spll_cntl2, par); /* - * The sclk has been started. However, I believe the first clock - * ticks it generates are not very stable. Hope this primitive loop - * helps for Rage Mobilities that sometimes crash when - * we switch to sclk. (Daniel Mantione, 13-05-2003) + * SCLK has been started. Wait for the PLL to lock. 5 ms + * should be enough according to mach64 programmer's guide. */ - for (i=0;i<=0x1ffff;i++); + mdelay(5); } aty_st_pll_ct(PLL_REF_DIV, pll->ct.pll_ref_div, par);
A similar but different patch just got merged into mainline:
commit 8690ba446defe2e2b81803756c099d2943dfd5fd
Author: David Miller [off-list ref]
Date: Mon Mar 5 01:35:36 2007 -0800
[PATCH] video/aty/mach64_ct.c: fix bogus delay loop
CT based mach64 cards were reported to hang on sparc64 boxes when
compiled with gcc-4.1.x and later.
Looking at this piece of code, it's no surprise. A critical
delay was implemented as an empty for() loop, and gcc 4.0.x
and previous did not optimize it away, so we did get a delay.
But gcc-4.1.x and later can optimize it away, and we get crashes.
Use a real udelay() to fix this. Fix verified on SunBlade100.
Signed-off-by: David S. Miller [off-list ref]
Signed-off-by: Linus Torvalds [off-list ref]
diff --git a/drivers/video/aty/mach64_ct.c b/drivers/video/aty/mach64_ct.c
index f3b487b..1fdcfdb 100644
--- a/drivers/video/aty/mach64_ct.c
+++ b/drivers/video/aty/mach64_ct.c@@ -598,7 +598,6 @@ static void aty_resume_pll_ct(const stru struct atyfb_par *par = info->par; if (par->mclk_per != par->xclk_per) { - int i; /* * This disables the sclk, crashes the computer as reported: * aty_st_pll_ct(SPLL_CNTL2, 3, info);
@@ -614,7 +613,7 @@ static void aty_resume_pll_ct(const stru * helps for Rage Mobilities that sometimes crash when * we switch to sclk. (Daniel Mantione, 13-05-2003) */ - for (i=0;i<=0x1ffff;i++); + udelay(500); } aty_st_pll_ct(PLL_REF_DIV, pll->ct.pll_ref_div, par);
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