linux-kernel - Re: [PATCH] PCI: qcom: Add interconnect bandwidth for PCIe Gen4

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Message-ID: <ZRFjAIYQQZnbNIdt@linaro.org>
Date:   Mon, 25 Sep 2023 13:37:52 +0300
From:   Abel Vesa <abel.vesa@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        lpieralisi@...nel.org, kw@...ux.com, andersson@...nel.org,
        bhelgaas@...gle.com, linux-arm-msm@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: qcom: Add interconnect bandwidth for PCIe Gen4

On 23-09-25 12:34:53, Konrad Dybcio wrote:
> On 25.09.2023 12:33, Abel Vesa wrote:
> > On 23-09-25 10:57:47, Konrad Dybcio wrote:
> >> On 24.09.2023 18:07, Manivannan Sadhasivam wrote:
> >>> PCIe Gen4 supports the interconnect bandwidth of 1969 MBps. So let's add
> >>> the bandwidth support in the driver. Otherwise, the default bandwidth of
> >>> 985 MBps will be used.
> >>>
> >>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> >>> ---
> >>>  drivers/pci/controller/dwc/pcie-qcom.c | 7 +++++--
> >>>  1 file changed, 5 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> >>> index 297442c969b6..6853123f92c1 100644
> >>> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> >>> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> >>> @@ -1384,11 +1384,14 @@ static void qcom_pcie_icc_update(struct qcom_pcie *pcie)
> >>>  	case 2:
> >>>  		bw = MBps_to_icc(500);
> >>>  		break;
> >>> +	case 3:
> >>> +		bw = MBps_to_icc(985);
> >>> +		break;
> >>>  	default:
> >>>  		WARN_ON_ONCE(1);
> >>>  		fallthrough;
> >>> -	case 3:
> >>> -		bw = MBps_to_icc(985);
> >>> +	case 4:
> >>> +		bw = MBps_to_icc(1969);
> >>>  		break;
> >> Are you adding case 4 under `default`? That looks.. bizzare..
> > 
> > That's intentional. You want it to use 1969MBps if there is a different
> > gen value. AFAIU.
> Gah right, then the commit message is wrong.

Yep, should be: "Otherwise, the default bandwidth of 1969 MBps will be
used."

But maybe we should not default to that. Maybe we should still default
to 985 MBps.

> 
> Konrad