linux-kernel - Re: [PATCH v8 3/7] PCI: qcom: Add ICC bandwidth vote for CPU to PCIe path

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Date: Fri, 5 Apr 2024 13:59:44 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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,
	linux-pci@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, vireshk@...nel.org,
	quic_vbadigan@...cinc.com, quic_skananth@...cinc.com,
	quic_nitegupt@...cinc.com, quic_parass@...cinc.com,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Subject: Re: [PATCH v8 3/7] PCI: qcom: Add ICC bandwidth vote for CPU to PCIe
 path

On Tue, Mar 05, 2024 at 04:23:21PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 3/4/2024 11:11 PM, Manivannan Sadhasivam wrote:
> > On Sat, Mar 02, 2024 at 09:29:57AM +0530, Krishna chaitanya chundru wrote:
> > > To access PCIe registers, PCIe BAR space, config space the CPU-PCIe
> > > ICC (interconnect consumers) path should be voted otherwise it may
> > > lead to NoC (Network on chip) timeout. We are surviving because of
> > > other driver vote for this path.
> > > 
> > > As there is less access on this path compared to PCIe to mem path
> > > add minimum vote i.e 1KBps bandwidth always.
> > 
> > Please add the info that 1KBps is what shared by the HW team.
> > 
> Ack to all the comments
> > > 
> > > When suspending, disable this path after register space access
> > > is done.
> > > 
> > > Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
> > > Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> > > ---
> > >   drivers/pci/controller/dwc/pcie-qcom.c | 38 ++++++++++++++++++++++++++++++++--
> > >   1 file changed, 36 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > index 10f2d0bb86be..a0266bfe71f1 100644
> > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c

[...]

> > > +	ret = icc_disable(pcie->icc_cpu);
> > > +	if (ret) {
> > > +		dev_err(dev, "failed to disable icc path of cpu-pcie: %d\n", ret);
> > 
> > "CPU-PCIe"
> > 
> > > +		if (pcie->suspended) {
> > > +			qcom_pcie_host_init(&pcie->pci->pp);
> > 
> > Interesting. So if icc_disable() fails, can the IP continue to function?
> > 
> As the ICC already enable before icc_disable() fails, the IP should work.

If icc_disable() fails, then most likely something is wrong with RPMh. How can
the IP continue to work in that case?

- Mani

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