applied. thanks, -Len >-----Original Message----- >From: Andreas Mohr [mailto:andi@xxxxxxxxxxxxxxxxxxxxxxx] >Sent: Monday, June 26, 2006 3:58 PM >To: Andrew Morton >Cc: Brown, Len; linux-acpi@xxxxxxxxxxxxxxx >Subject: [PATCH -mm] ACPI: re-add important comment about >P_LVLx register > >Hi all, > >- re-add explanatory comment to P_LVLx invocation that had been removed > a while ago > >While trying to look for superfluous I/O accesses that can be optimized >away, I stumbled upon this ACPI sleep I/O access and couldn't >figure out >why the hell this dummy op was necessary. >After more than one hour of internet research, I had collected >a sufficient >number of documents (among those very old kernel versions) that finally >told me what this dummy read was about: STPCLK# doesn't get >asserted in time >on (some) chipsets, which is why we need to have a dummy I/O >read to delay >further instruction processing until the CPU is fully stopped. > >Compile-tested on 2.6.17-mm1. > >Signed-off-by: Andreas Mohr <andi@xxxxxxxx> > > >diff -urN linux-2.6.17-mm2.orig/drivers/acpi/processor_idle.c >linux-2.6.17-mm2.my/drivers/acpi/processor_idle.c >--- linux-2.6.17-mm2.orig/drivers/acpi/processor_idle.c >2006-06-26 11:18:52.000000000 +0200 >+++ linux-2.6.17-mm2.my/drivers/acpi/processor_idle.c >2006-06-26 18:06:18.000000000 +0200 >@@ -361,7 +361,9 @@ > t1 = inl(acpi_fadt.xpm_tmr_blk.address); > /* Invoke C2 */ > inb(cx->address); >- /* Dummy op - must do something useless after >P_LVL2 read */ >+ /* Dummy wait op - must do something useless >after P_LVL2 read >+ because chipsets cannot guarantee that STPCLK# signal >+ gets asserted in time to freeze execution >properly. */ > t2 = inl(acpi_fadt.xpm_tmr_blk.address); > /* Get end time (ticks) */ > t2 = inl(acpi_fadt.xpm_tmr_blk.address); >@@ -399,7 +401,7 @@ > t1 = inl(acpi_fadt.xpm_tmr_blk.address); > /* Invoke C3 */ > inb(cx->address); >- /* Dummy op - must do something useless after >P_LVL3 read */ >+ /* Dummy wait op (see above) */ > t2 = inl(acpi_fadt.xpm_tmr_blk.address); > /* Get end time (ticks) */ > t2 = inl(acpi_fadt.xpm_tmr_blk.address); > - To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
