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 16:19:49 +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 7/26/2023 2:52 PM, Praveenkumar I wrote:
>
> 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.
> Sorry, if I do so, then the above mentioned issue will come here as 
> well right?
>
> This one: 
> https://lore.kernel.org/all/20230608093652.1409485-1-vidyas@nvidia.com/
Sorry, confused a bit here. After moving the MPS setting to post_init, 
pci_configure_mps() is taking care if 128 byte PCIe device is connected.
Posted a updated patch.

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