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

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Date:   Wed, 26 Jul 2023 12:58:28 +0530
From:   Praveenkumar I <quic_ipkumar@...cinc.com>
To:     Manivannan Sadhasivam <mani@...nel.org>
CC:     Konrad Dybcio <konrad.dybcio@...aro.org>, <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 7/25/2023 11:36 AM, Manivannan Sadhasivam wrote:
> On Tue, Jul 25, 2023 at 10:16:04AM +0530, Praveenkumar I wrote:
>> 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)/
> Ok. But for setting MPS, you need to change the DEVCTL register in post_init
> sequence for IPQ9574. It is not a quirk, so you cannot use fixups.
Sure, will add in post_init of IPQ9574.

--
Thanks,
Praveenkumar
>
> - Mani
>
>>>> - Mani
>>>>
>>>>> Konrad
>>>> -- 
>>>> மணிவண்ணன் சதாசிவம்
>> --
>> Thanks,
>> Praveenkumar