linux-kernel - Re: [PATCH v2] PCI: qcom: Set max payload size 256 bytes for IPQ9574

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Date:   Mon, 20 Nov 2023 14:23:14 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Praveenkumar I <quic_ipkumar@...cinc.com>
Cc:     mani@...nel.org, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...aro.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 v2] PCI: qcom: Set max payload size 256 bytes for IPQ9574

On Wed, Jul 26, 2023 at 04:12:49PM +0530, Praveenkumar I wrote:
> This patch sets 256 bytes as payload size for IPQ9574. This allows
> PCIe RC to use the max payload size when a capable link partner is
> connected.

I'm confused because this patch doesn't apply to v6.7-rc1, and I don't
see qcom_pcie_post_init_1_27_0() or IPQ9574 mentioned in the git
history.  Maybe this depends on some out-of-tree patch?

I think this commit log should explain why the existing code in the
PCI core doesn't do what's needed.  Is there something qcom-specific
about this issue?

Maybe an example including the DEVCAP Max_Payload_Size Supported and
the DEVCTL Max_Payload_Size for both ends of the link would help
understand what's going wrong.

Does this setting get lost after suspend?  Does it need to be updated
again after suspend/resume?

> Signed-off-by: Praveenkumar I <quic_ipkumar@...cinc.com>
> ---
> [v2]:
> 	Dropped cover letter for this patch. Configured the max payload
> 	in the post_init of IPQ9574 instead for early fixup.
> 
>  drivers/pci/controller/dwc/pcie-qcom.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 8ee7c2b5de27..739c0d514a96 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -1145,6 +1145,15 @@ static int qcom_pcie_post_init(struct qcom_pcie *pcie)
>  
>  static int qcom_pcie_post_init_1_27_0(struct qcom_pcie *pcie)
>  {
> +	struct dw_pcie *pci = pcie->pci;
> +	u16 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> +	u32 val;
> +
> +	val = readl(pci->dbi_base + offset + PCI_EXP_DEVCTL);
> +	val &= ~PCI_EXP_DEVCTL_PAYLOAD;
> +	val |= PCI_EXP_DEVCTL_PAYLOAD_256B;
> +	writel(val, pci->dbi_base + offset + PCI_EXP_DEVCTL);
> +
>  	writel(SLV_ADDR_SPACE_SZ_1_27_0,
>  	       pcie->parf + PARF_SLV_ADDR_SPACE_SIZE);
>  
> -- 
> 2.34.1
>