Re: [PATCH v1] ACPI/IORT: Workaround for IORT ID count "minus one" issue

Hanjun Guo
2020-01-03T10:23:19Z

On 2020/1/2 19:18, John Garry wrote:
> +
>
> On 30/12/2019 12:27, Guohanjun (Hanjun Guo) wrote:
>> The IORT spec [0] says Number of IDs = The number of IDs in the range minus
>> one, it is confusing but it was written down in the first version of the
>> IORT spec. But the IORT ID mapping function iort_id_map() did something
>> wrong from the start, which bails out if:
>>
>> the request ID >= the input base + number of IDs
>>
>> This is wrong because it ignored the "minus one", and breaks some valid
>> usecases such as ID mapping to contain single device mapping without
>> single mapping flag set.
>>
>> Pankaj Bansal proposed a solution to fix the issue [1], which bails
>> out if:
>>
>> the request ID > the input base + number of IDs
>>
>> This works as the spec defined, unfortunately some firmware didn't
>> minus one for the number of IDs in the range, and the propoased
>> solution will break those systems in this way:
>>
>> PCI hostbridge mapping entry 1:
>> Input base:  0x1000
>> ID Count:    0x100
>> Output base: 0x1000
>> Output reference: 0xC4  //ITS reference
>>
>> PCI hostbridge mapping entry 2:
>> Input base:  0x1100
>> ID Count:    0x100
>> Output base: 0x2000
>> Output reference: 0xD4  //ITS reference
>>
>> Two mapping entries which the second entry's Input base = the first
>> entry's Input base + ID count, so for requester ID 0x1100 will map
>> to ITS 0xC4 not 0xD4 if we update '>=' to '>'.
>>
>> So introduce a workaround to match the IORT's OEM information for
>> the broken firmware, also update the logic of the ID mapping for
>> firmwares report the number of IDs as the IORT spec defined, to
>> make the code compatible for both kinds of system.
>>
>> I checked the ACPI tables in the tianocore/edk2-platforms [2],
>
> Hi Hanjun,
>
> only
>> HiSilicon HIP07/08 did wrong, so just add HIP07/08 to the workaround
>> info table,
>
> Are you asserting that other platforms are ok on the basis that NumIds = large power of 2 - 1, e.g. 0xffff? Is this strictly proper?

No, some platforms with no opensource ACPI tables, are
not covered.

>
> if we break other platforms, we can add that later.
>>
>
> I think that it would be better to audit others now as well as best as reasonably possible. There is somewhat limited coverage in [2].

I will Cc people form Mavell, Ampere, and Ard who is know Socionext very well,
that's the best I can do.

Thanks
Hanjun