linux-kernel - Re: [PATCH 1/1] PCI: qcom: Add early fixup to set the max payload size for IPQ9574

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Date:   Tue, 25 Jul 2023 10:16:04 +0530
From:   Praveenkumar I <quic_ipkumar@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>
CC:     <agross@...nel.org>, <andersson@...nel.org>,
        <lpieralisi@...nel.org>, <kw@...ux.com>, <robh@...nel.org>,
        <bhelgaas@...gle.com>, <linux-pci@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_varada@...cinc.com>, <quic_devipriy@...cinc.com>
Subject: Re: [PATCH 1/1] PCI: qcom: Add early fixup to set the max payload
 size for IPQ9574


On 7/24/2023 7:39 PM, Manivannan Sadhasivam wrote:
> On Mon, Jul 24, 2023 at 06:38:55PM +0530, Manivannan Sadhasivam wrote:
>> On Mon, Jul 24, 2023 at 02:53:37PM +0200, Konrad Dybcio wrote:
>>> On 24.07.2023 14:47, Praveenkumar I wrote:
>>>> Set 256 bytes as payload size for IPQ9574 via early fixup. This allows
>>>> PCIe RC to use the max payload size when a capable link partner is
>>>> connected.
>>>>
>>>> Signed-off-by: Praveenkumar I <quic_ipkumar@...cinc.com>
>>>> ---
>>> [...]
>>>
>>>> +static void qcom_fixup_mps_256(struct pci_dev *dev)
>>>> +{
>>>> +	pcie_set_mps(dev, 256);
>>> Looks like setting "dev->pcie_mpss = 1" here would make the PCIe generic
>>> code take care of this.
>>>
>> Right, also this setting should not be PCI-PCI bridge specific but rather
>> controller specific.
>>
> Wait, have you tested this patch with PCIe devices having MPS < 256 i.e.,
> default 128?
>
> Take a look at this discussion: https://lore.kernel.org/all/20230608093652.1409485-1-vidyas@nvidia.com/
>
> - Mani
Yes, tested this patch with PCIe devices having default 128 and RC is 
falling back to 128 when pci device is added.
This is handled inside pci_configure_mps().
/        mpss = 128 << dev->pcie_mpss;/
/        if (mpss < p_mps && pci_pcie_type(bridge) == 
PCI_EXP_TYPE_ROOT_PORT) {/
/                pcie_set_mps(bridge, mpss);/
/                pci_info(dev, "Upstream bridge's Max Payload Size set 
to %d (was %d, max %d)\n",/
/                         mpss, p_mps, 128 << bridge->pcie_mpss);/
/                p_mps = pcie_get_mps(bridge);/
/        }/
//
Also getting the below print,
/[    2.011963] pci 0003:01:00.0: Upstream bridge's Max Payload Size set 
to 128 (was 256, max 256)/
>> - Mani
>>
>>> Konrad
>> -- 
>> மணிவண்ணன் சதாசிவம்
--
Thanks,
Praveenkumar