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

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Date:   Mon, 25 Sep 2023 12:34:53 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Abel Vesa <abel.vesa@...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 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.

Konrad