Re: [PATCH v6 3/6] PCI: qcom: Add missing icc bandwidth vote for cpu to PCIe path

Konrad Dybcio
2024-01-17T09:13:23Z

On 1/16/24 11:52, Johan Hovold wrote:
> On Fri, Jan 12, 2024 at 11:33:15PM +0100, Konrad Dybcio wrote:
>> On 12.01.2024 16:17, Bryan O'Donoghue wrote:
>>> On 12/01/2024 14:22, Krishna chaitanya chundru wrote:
>>>> CPU-PCIe path consits for registers PCIe BAR space, config space.
>>>> As there is less access on this path compared to pcie to mem path
>>>> add minimum vote i.e GEN1x1 bandwidth always.
>>>>
>>>> In suspend remove the cpu vote after register space access is done.
>>>>
>>>> Fixes: c4860af88d0c ("PCI: qcom: Add basic interconnect support")
>>>
>>> If this patch is a Fixes then don't you need the accompanying dts change as a parallel Fixes too ?
>>>
>>> i.e. without the dts update - you won't have the nodes in the dts to consume => applying this code to the stable kernel absent the dts will result in no functional change and therefore no bugfix.
>>
>> The Fixes tag denotes a bug fix, its use for backport autosel is just
>> a nice "coincidence".
>>
>> Fixing a lack of a required icc path and having to rely on BL leftovers
>> / keepalive bus settings is definitely worth this tag in my eyes.
>
> An incomplete implementation can sometimes be considered a bug, but not
> always. If this is needed to enable a new use case, then it's hard to
> argue that the original omission was a bug.
>
> And as I just mentioned to Krishna, the above Fixes tag is not correct
> as that commit did not *introduce* any issue. It solved the bit that was
> strictly needed for sc8280xp, but now it seems you may need something
> more for an even newer platform (even if no details and motivation was
> included in the commit message as it should have been).

The PCIe hardware seems to be piggybacking off of others' bus
bandwidth requests and I think it's just been pure luck that
it didn't simply refuse to work on previous generations.

So indeed, the commit message seems incomplete in explaining
where the problem lies

Konrad