Commit-ID: 4c45c5167c9563b1a2eee3e2fe954621355e4ca8 Gitweb: http://git.kernel.org/tip/4c45c5167c9563b1a2eee3e2fe954621355e4ca8 Author: Jiri Slaby <jsl...@suse.cz> AuthorDate: Thu, 19 Jan 2017 12:47:30 +0100 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Sun, 22 Jan 2017 10:03:12 +0100
x86/timer: Make delay() work during early bootup When a panic happens during bootup, "Rebooting in X seconds.." is shown, but reboot happens immediatelly. It is because panic() uses mdelay() and mdelay() calls __const_udelay() immediately, which does not work while booting. The per_cpu cpu_info.loops_per_jiffy value is not initialized yet, so __const_udelay() actually multiplies the number of loops by zero. This results in __const_udelay() to delay the execution only by a nanosecond or so. So check whether cpu_info.loops_per_jiffy is zero and use loops_per_jiffy in that case. mdelay() will not be so precise without proper calibration, but it works relatively well. Before: [ 0.170039] delaying 100ms [ 0.170828] done After [ 0.214042] delaying 100ms [ 0.313974] done I do not think the added check matters given we are about to spin the processor in the next few hundred cycles. Signed-off-by: Jiri Slaby <jsl...@suse.cz> Reviewed-by: Andy Shevchenko <andy.shevche...@gmail.com> Acked-by: Thomas Gleixner <t...@linutronix.de> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/r/20170119114730.2670-1-jsl...@suse.cz [ Minor edits. ] Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/lib/delay.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c index 073d1f1..a8e91ae 100644 --- a/arch/x86/lib/delay.c +++ b/arch/x86/lib/delay.c @@ -156,13 +156,13 @@ EXPORT_SYMBOL(__delay); inline void __const_udelay(unsigned long xloops) { + unsigned long lpj = this_cpu_read(cpu_info.loops_per_jiffy) ? : loops_per_jiffy; int d0; xloops *= 4; asm("mull %%edx" :"=d" (xloops), "=&a" (d0) - :"1" (xloops), "0" - (this_cpu_read(cpu_info.loops_per_jiffy) * (HZ/4))); + :"1" (xloops), "0" (lpj * (HZ / 4))); __delay(++xloops); }
