Messages in this thread Patch in this message | | | Date | Wed, 20 Feb 2008 13:06:22 +0100 | From | Rene Herman <> | Subject | Re: [PATCH] x86: use explicit timing delay for pit accesses in kernel and pcspkr driver |
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On 18-02-08 23:44, H. Peter Anvin wrote:
>>>> Rene Herman wrote: >>>>> >>>>> Yes, but generally not any P5+ system is going to need the PIT >>>>> delay in the first place meaning it just doesn't matter. There were >>>>> the VIA issues with the PIC but unless I missed it not with the PIT. >>>>> >>>> >>>> Uhm, I'm not sure I believe that's safe. >>>> >>>> The PIT is particularly pissy in this case -- the semantics of the >>>> PIT are ill-defined if there hasn't been a PIT clock between two >>>> adjacent accesses, so I fully expect that there are chipsets out >>>> there which will do very bad things in this case. >>> >>> Okay. Now that they're isolated, do you have a suggestion for >>> {in,out}b_pit? You say a PIT clock, so do you think we can bounce of >>> the PIT iself in this case after all? >> >> Am I correct that channel 1 is never used? A simple read from 0x41? >> > > Channel 1 is available for the system. In modern systems, it's pretty > much available for the OS, although that's never formally stated (in the > original PC, it was used for DRAM refresh.) > > However, I could very easily see a chipset have issues with that kind of > stuff.
I couldn't really, but clean it's neither. Okay, so you just want something like this? This initializes loops_per_jiffy somewhat more usefully -- at a 1G CPU for P6 and 64-bit, and tuning it down again for 386/486/586.
The values taken are for what I believe to be the fastest CPUs among the specific family. Alan?
386-40 and P1-233 were verified, the 486-120 value was scaled from a 486-40.
_Something_ like this would seem to be the only remaining option. It seems fairly unuseful to #ifdef around that switch statement for kernels without support for the earlier families, but if you insist...
Rene. commit 9c679215248e837b34242632d5a22adf9a247021 Author: Rene Herman <rene.herman@gmail.com> Date: Wed Feb 20 12:52:30 2008 +0100
x86: per CPU family loops_per_jiffy initialization
Following the current port 0x80 I/O delay replacements we need microseconds to be somewhat usefully defined pre calibration.
Initialize 386, 486 and Pentium 1 as fastest in their families and higher CPUs (including 64-bit) at 1 Ghz. Note that trouble should be absent past family 5 systems anyway.
Signed-off-by: Rene Herman <rene.herman@gmail.com>
diff --git a/arch/x86/kernel/time_32.c b/arch/x86/kernel/time_32.c index 1a89e93..e33e70b 100644 --- a/arch/x86/kernel/time_32.c +++ b/arch/x86/kernel/time_32.c @@ -32,6 +32,7 @@ #include <linux/interrupt.h> #include <linux/time.h> #include <linux/mca.h> +#include <linux/delay.h> #include <asm/arch_hooks.h> #include <asm/hpet.h> @@ -134,6 +135,17 @@ void __init hpet_time_init(void) */ void __init time_init(void) { + switch (boot_cpu_data.x86) { + case 3: + loops_per_jiffy = LOOPS_PER_JIFFY_386; + break; + case 4: + loops_per_jiffy = LOOPS_PER_JIFFY_486; + break; + case 5: + loops_per_jiffy = LOOPS_PER_JIFFY_586; + break; + } tsc_init(); late_time_init = choose_time_init(); } diff --git a/include/asm-x86/delay.h b/include/asm-x86/delay.h index 409a649..d0fbaf6 100644 --- a/include/asm-x86/delay.h +++ b/include/asm-x86/delay.h @@ -7,6 +7,11 @@ * Delay routines calling functions in arch/x86/lib/delay.c */ +#define LOOPS_PER_JIFFY_386 (4000000 / HZ) /* 386 at 40 Mhz */ +#define LOOPS_PER_JIFFY_486 (30000000 / HZ) /* 486 at 120 MHz */ +#define LOOPS_PER_JIFFY_586 (233000000 / HZ) /* Pentium 1 at 233 Mhz */ +#define LOOPS_PER_JIFFY (1000000000 / HZ) /* P6+ at 1 GHz */ + /* Undefined functions to get compile-time errors */ extern void __bad_udelay(void); extern void __bad_ndelay(void); diff --git a/init/main.c b/init/main.c index 8b19820..94862c8 100644 --- a/init/main.c +++ b/init/main.c @@ -228,12 +228,11 @@ static int __init obsolete_checksetup(char *line) return had_early_param; } -/* - * This should be approx 2 Bo*oMips to start (note initial shift), and will - * still work even if initially too large, it will just take slightly longer - */ -unsigned long loops_per_jiffy = (1<<12); +#ifndef LOOPS_PER_JIFFY +#define LOOPS_PER_JIFFY (1 << 12) +#endif +unsigned long loops_per_jiffy = LOOPS_PER_JIFFY; EXPORT_SYMBOL(loops_per_jiffy); static int __init debug_kernel(char *str) | |