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

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Message-ID: <20230725060635.GA22139@thinkpad>
Date:   Tue, 25 Jul 2023 11:36:35 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Praveenkumar I <quic_ipkumar@...cinc.com>
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 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.

- Mani

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

-- 
மணிவண்ணன் சதாசிவம்