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

[Jan Beulich <jbeulich@xxxxxxxx>]

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)) {
                        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();