Re: [Xen-devel] [PATCH 2/3] Fix acpi_set_register

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

acpi_set_register() is doing a read-modify-write of PM2_CONTROL. It's only
safe to skip the read if the modification is going to obliterate all old
bits. Is the read really that expensive (and equally, in patch 3, is the
write of ARB_DIS really that expensive)?

 -- Keir

On 3/9/08 02:52, "Wei, Gang" <gang.wei@xxxxxxxxx> wrote:

> ACPI: Remove a redundant call to acpi_hw_register_read().
> 
> Signed-off-by: Wei Gang <gang.wei@xxxxxxxxx>
> 
> diff -r fc0b0c64246d xen/drivers/acpi/hwregs.c
> --- a/xen/drivers/acpi/hwregs.c Thu Aug 21 16:15:30 2008 +0800
> +++ b/xen/drivers/acpi/hwregs.c Mon Aug 25 15:24:32 2008 +0800
> @@ -238,12 +238,6 @@ acpi_status acpi_set_register(u32 regist
>                 break;
> 
>         case ACPI_REGISTER_PM2_CONTROL:
> -
> -               status = acpi_hw_register_read(ACPI_REGISTER_PM2_CONTROL,
> -                                              &register_value);
> -               if (ACPI_FAILURE(status)) {
> -                       goto unlock_and_exit;
> -               }
> 
>                 ACPI_DEBUG_PRINT((ACPI_DB_IO,
>                                   "PM2 control: Read %X from %8.8X%8.8X\n",
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