Re: [patch 2/6] acpi: check _PSS invalidation when BIOS report _PSS with 0x80000000

[Len Brown <lenb@kernel.org>]

I recall nacking this one some time ago.

ACPI_PROCESSOR_PSS_INVALID is fantasy.
Can't we be smarter about detecting and handling
BIOS bugs, and not pretend that the specification
tells us that this particular bit pattern is invalid (it does not)
What happens when the next BIOS gives us 0x40000000?

thanks
Len Brown, Intel Open Source Technology Center

On Fri, 9 Jan 2009, akpm@linux-foundation.org wrote:

> From: Youquan, Song <youquan.song@intel.com>
> 
> When cpu frequencey scaling is disabled, some BIOSes report _PSS with all
> 0x80000000.  If the kernel treats this case as valid, the kernel will boot
> crash when load cpufreq govenors.
> 
> So in order to cover more buggy BIOSs, the patch just check _PSS core
> frequency invalidation.
> 
> Signed-off-by: Youquan, Song <youquan.song@intel.com>
> Signed-off-by: Pallipadi, Venkatesh <venkatesh.pallipadi@intel.com>
> Cc: Len Brown <lenb@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  drivers/acpi/processor_perflib.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff -puN drivers/acpi/processor_perflib.c~acpi-check-_pss-invalidation-when-bios-report-_pss-with-all-0x80000000 drivers/acpi/processor_perflib.c
> --- a/drivers/acpi/processor_perflib.c~acpi-check-_pss-invalidation-when-bios-report-_pss-with-all-0x80000000
> +++ a/drivers/acpi/processor_perflib.c
> @@ -50,6 +50,7 @@
>  #define ACPI_PROCESSOR_CLASS		"processor"
>  #define ACPI_PROCESSOR_FILE_PERFORMANCE	"performance"
>  #define _COMPONENT		ACPI_PROCESSOR_COMPONENT
> +#define ACPI_PROCESSOR_PSS_INVALID	0x80000000
>  ACPI_MODULE_NAME("processor_perflib");
>  
>  static DEFINE_MUTEX(performance_mutex);
> @@ -324,6 +325,14 @@ static int acpi_processor_get_performanc
>  			kfree(pr->performance->states);
>  			goto end;
>  		}
> +
> +		if (px->core_frequency == ACPI_PROCESSOR_PSS_INVALID) {
> +			printk(KERN_ERR PREFIX
> +				    "P-states disabled in the BIOS\n");
> +			result = -EFAULT;
> +			kfree(pr->performance->states);
> +			goto end;
> +		}
>  	}
>  
>        end:
> _
>