Re: [PATCH v2 08/13] ACPICA: Hardware: Add optimized access bit width support

Boris Ostrovsky
2016-05-26T21:59:40Z

On 05/26/2016 12:55 PM, Boris Ostrovsky wrote:
> On 05/26/2016 12:26 PM, Jan Beulich wrote:
>>>>> Boris Ostrovsky <boris.ostrovsky@oracle.com> 05/25/16 9:17 PM >>>
>>> On 05/05/2016 12:58 AM, Lv Zheng wrote:
>>>> +static u8
>>>> +acpi_hw_get_access_bit_width(struct acpi_generic_address *reg, u8 max_bit_width)
>>>> +{
>>>> + u64 address;
>>>> +
>>>> + if (!reg->access_width) {
>>>> + /*
>>>> + * Detect old register descriptors where only the bit_width field
>>>> + * makes senses. The target address is copied to handle possible
>>>> + * alignment issues.
>>>> + */
>>>> + ACPI_MOVE_64_TO_64(&address, &reg->address);
>>>> + if (!reg->bit_offset && reg->bit_width &&
>>>> + ACPI_IS_POWER_OF_TWO(reg->bit_width) &&
>>>> + ACPI_IS_ALIGNED(reg->bit_width, 8) &&
>>>> + ACPI_IS_ALIGNED(address, reg->bit_width)) {
>>>> + return (reg->bit_width);
>>>> + } else {
>>>> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) {
>>>> + return (32);
>>> This (together with "... Add access_width/bit_offset support in
>>> acpi_hw_write") breaks Xen guests using older QEMU which doesn't support
>>> 4-byte IO accesses.
>>>
>>> Why not return "reg->bit_width?:max_bit_width" ? This will preserve
>>> original behavior.
>> Did you figure out why we get here in the first place, instead of taking the
>> first "return"? I.e. isn't the issue the apparently wrong use of the second
>> ACPI_IS_ALIGNED() above? Afaict it ought to be
>> ACPI_IS_ALIGNED(address, reg->bit_width / 8)...
> We are trying to access address 0x...b004 (PM1a control) so yes, fixing
> alignment check would probably resolve the problem that we are seeing now.
>
> However, for compatibility purposes we may consider not doing any checks
> and simply return bit_width if access_width is not available.

Interestingly enough I bisected what I thought was a completely
different problem to this patch as well.

Something is messed up with 32-bit dom0 booting (so no QEMU) on one
machine in my pool. First error that I see is
pcieport 0000:00:02.0: can't find IRQ for PCI INT A; probably buggy
MP table

I'll look at this tomorrow, hopefully.

-boris