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

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Date: Fri, 12 Jan 2024 23:37:03 +0100
From: Konrad Dybcio <konrad.dybcio@...aro.org>
To: Johan Hovold <johan@...nel.org>,
 Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Manivannan Sadhasivam <mani@...nel.org>,
 Rob Herring <robh+dt@...nel.org>, Johan Hovold <johan+linaro@...nel.org>,
 Brian Masney <bmasney@...hat.com>, Georgi Djakov <djakov@...nel.org>,
 linux-arm-msm@...r.kernel.org, vireshk@...nel.org,
 quic_vbadigan@...cinc.com, quic_skananth@...cinc.com,
 quic_nitegupt@...cinc.com, linux-pci@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH v6 3/6] PCI: qcom: Add missing icc bandwidth vote for cpu
 to PCIe path

On 12.01.2024 16:59, Johan Hovold wrote:
> On Fri, Jan 12, 2024 at 07:52:02PM +0530, Krishna chaitanya chundru wrote:
>> CPU-PCIe path consits for registers PCIe BAR space, config space.
> 
> consits?
> 
>> As there is less access on this path compared to pcie to mem path
>> add minimum vote i.e GEN1x1 bandwidth always.
> 
> gen1 bandwidth can't be right.
> 
>> In suspend remove the cpu vote after register space access is done.
>>
>> Fixes: c4860af88d0c ("PCI: qcom: Add basic interconnect support")
>> cc: stable@...r.kernel.org
> 
> This does not look like a fix so drop the above.
> 
> The commit you refer to explicitly left this path unconfigured for now
> and only added support for the configuring the mem path as needed on
> sc8280xp which otherwise would crash.

I only sorta agree. I'd include a fixes tag but point it to either 8450
addition or original driver introduction, as this is patching up a real
hole (see my reply to Bryan).

> 
>> @@ -1573,7 +1588,7 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
>>  	 */
>>  	ret = icc_set_bw(pcie->icc_mem, 0, kBps_to_icc(1));
>>  	if (ret) {
>> -		dev_err(dev, "Failed to set interconnect bandwidth: %d\n", ret);
>> +		dev_err(dev, "Failed to set interconnect bandwidth for pcie-mem: %d\n", ret);
>>  		return ret;
>>  	}
>>  
>> @@ -1597,6 +1612,12 @@ static int qcom_pcie_suspend_noirq(struct device *dev)
>>  		pcie->suspended = true;
>>  	}
>>  
>> +	/* Remove cpu path vote after all the register access is done */
>> +	ret = icc_set_bw(pcie->icc_cpu, 0, 0);
> 
> I believe you should use icc_disable() here.

Oh, TIL this exists!

Konrad