Re: [PATCH 1/1] x86/acpi: Use FADT flags to determine the PMTMR width

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Jun 16, 2020 at 03:25:42PM +0200, Jan Beulich wrote:
> On 16.06.2020 12:32, Roger Pau Monné wrote:
> > On Tue, Jun 16, 2020 at 10:07:05AM +0200, Jan Beulich wrote:
> >> On 14.06.2020 16:36, Grzegorz Uriasz wrote:
> >>> --- a/xen/arch/x86/acpi/boot.c
> >>> +++ b/xen/arch/x86/acpi/boot.c
> >>> @@ -480,7 +480,10 @@ static int __init acpi_parse_fadt(struct acpi_table_header *table)
> >>>  		if (fadt->xpm_timer_block.space_id ==
> >>>  		    ACPI_ADR_SPACE_SYSTEM_IO) {
> >>>  			pmtmr_ioport = fadt->xpm_timer_block.address;
> >>> -			pmtmr_width = fadt->xpm_timer_block.bit_width;
> >>> +			if (fadt->flags & ACPI_FADT_32BIT_TIMER)
> >>> +				pmtmr_width = 32;
> >>> +			else
> >>> +				pmtmr_width = 24;
> >>
> >> I think disagreement of the two wants logging, and you want to
> >> default to using the smaller of the two (or even to ignoring the
> >> timer altogether). Then there wants to be a way to override
> >> (unless we already have one) our defaulting, in case it's wrong.
> > 
> > TBH, I presume timer_block will always return 32bits, because that's
> > the size of the register. Then the timer can implement less bits than
> > the full size of the register, and that's what gets signaled using the
> > ACPI flags. What we care about here is the number of bits used by the
> > timer, not the size of the register.
> > 
> > I think we should only ignore the timer if pm_timer_block.bit_width <
> > pmtmr_width.
> > 
> > Printing a (debug) message when those values disagree is fine, but I
> > bet it's going to trigger always when the implemented timer is only
> > using 24bits.
> 
> The 2nd system I tried on would trigger it, so maybe there's no point
> in logging indeed. How about the below as a basis?
> 
> Jan
> 
> --- unstable.orig/xen/arch/x86/acpi/boot.c
> +++ unstable/xen/arch/x86/acpi/boot.c
> @@ -480,7 +480,9 @@ static int __init acpi_parse_fadt(struct
>  	if (fadt->header.revision >= FADT2_REVISION_ID) {
>  		/* FADT rev. 2 */
>  		if (fadt->xpm_timer_block.space_id ==
> -		    ACPI_ADR_SPACE_SYSTEM_IO) {
> +		    ACPI_ADR_SPACE_SYSTEM_IO &&
> +		    (fadt->xpm_timer_block.access_width == 0 ||
> +		     fadt->xpm_timer_block.access_width == 3)) {

We should really have defines for those values, or else they seem to
imply actual access sizes. What about adding
ACPI_ADDR_ACCESS_{LEGACY,BYTE,WORD,DWORD,QWORD}?

Also the check for the access size seems kind of unrelated to the
patch itself? (not that I'm opposed to it)

>  			pmtmr_ioport = fadt->xpm_timer_block.address;
>  			pmtmr_width = fadt->xpm_timer_block.bit_width;
>  		}
> @@ -492,8 +494,10 @@ static int __init acpi_parse_fadt(struct
>   	 */
>  	if (!pmtmr_ioport) {
>  		pmtmr_ioport = fadt->pm_timer_block;
> -		pmtmr_width = fadt->pm_timer_length == 4 ? 24 : 0;
> +		pmtmr_width = fadt->pm_timer_length == 4 ? 32 : 0;
>  	}
> +	if (pmtmr_width > 24 && !(fadt->flags & ACPI_FADT_32BIT_TIMER))
> +		pmtmr_width = 24;
>  	if (pmtmr_ioport)
>  		printk(KERN_INFO PREFIX "PM-Timer IO Port: %#x (%u bits)\n",
>  		       pmtmr_ioport, pmtmr_width);
> --- unstable.orig/xen/arch/x86/time.c
> +++ unstable/xen/arch/x86/time.c
> @@ -465,7 +465,7 @@ static s64 __init init_pmtimer(struct pl
>      u64 start;
>      u32 count, target, mask = 0xffffff;
>  
> -    if ( !pmtmr_ioport || !pmtmr_width )
> +    if ( !pmtmr_ioport )
>          return 0;
>  
>      if ( pmtmr_width == 32 )
> @@ -473,6 +473,8 @@ static s64 __init init_pmtimer(struct pl
>          pts->counter_bits = 32;
>          mask = 0xffffffff;
>      }
> +    else if ( pmtmr_width != pts->counter_bits )
> +        return 0;
>  
>      count = inl(pmtmr_ioport) & mask;
>      start = rdtsc_ordered();

The rest LGTM.

Thanks, Roger.