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Message-ID: <ca4f3f38-f0e5-4d10-b9eb-155f6ffbc57c@linaro.org>
Date: Wed, 17 Jan 2024 10:13:15 +0100
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Subject: Re: [PATCH v6 3/6] PCI: qcom: Add missing icc bandwidth vote for cpu
 to PCIe path
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To: Johan Hovold <johan@kernel.org>
Cc: Bryan O'Donoghue <bryan.odonoghue@linaro.org>,
 Krishna chaitanya chundru <quic_krichai@quicinc.com>,
 Bjorn Andersson <andersson@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
 Lorenzo Pieralisi <lpieralisi@kernel.org>,
 =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= <kw@linux.com>,
 Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>, Manivannan Sadhasivam <mani@kernel.org>,
 Rob Herring <robh+dt@kernel.org>, Johan Hovold <johan+linaro@kernel.org>,
 Brian Masney <bmasney@redhat.com>, Georgi Djakov <djakov@kernel.org>,
 linux-arm-msm@vger.kernel.org, vireshk@kernel.org,
 quic_vbadigan@quicinc.com, quic_skananth@quicinc.com,
 quic_nitegupt@quicinc.com, linux-pci@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
 stable@vger.kernel.org
References: <20240112-opp_support-v6-0-77bbf7d0cc37@quicinc.com>
 <20240112-opp_support-v6-3-77bbf7d0cc37@quicinc.com>
 <fecfd2d9-7302-4eb6-92d0-c2efbe824bf4@linaro.org>
 <f9a177e0-3698-4865-9463-220c65c653fb@linaro.org>
 <ZaZf4EyX5oADXG9N@hovoldconsulting.com>
From: Konrad Dybcio <konrad.dybcio@linaro.org>
In-Reply-To: <ZaZf4EyX5oADXG9N@hovoldconsulting.com>
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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