linux-kernel - Re: [PATCH 2/2] PCI: qcom-ep: Implement dbi_cs2_access() function callback for DBI CS2 access

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Date:   Tue, 17 Oct 2023 07:24:31 -0700
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
CC:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH 2/2] PCI: qcom-ep: Implement dbi_cs2_access() function
 callback for DBI CS2 access

On Tue, Oct 17, 2023 at 11:47:55AM +0530, Manivannan Sadhasivam wrote:
> From: Manivannan Sadhasivam <mani@...nel.org>

Your S-o-b should match this.

> 
> Qcom EP platforms require enabling/disabling the DBI CS2 access while
> programming some read only and shadow registers through DBI. So let's
> implement the dbi_cs2_access() callback that will be called by the DWC core
> while programming such registers like BAR mask register.
> 
> Without DBI CS2 access, writes to those registers will not be reflected.
> 
> Fixes: f55fee56a631 ("PCI: qcom-ep: Add Qualcomm PCIe Endpoint controller driver")
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom-ep.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> index 32c8d9e37876..4653cbf7f9ed 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> @@ -124,6 +124,7 @@
>  
>  /* ELBI registers */
>  #define ELBI_SYS_STTS				0x08
> +#define ELBI_CS2_ENABLE				0xa4
>  
>  /* DBI registers */
>  #define DBI_CON_STATUS				0x44
> @@ -262,6 +263,18 @@ static void qcom_pcie_dw_stop_link(struct dw_pcie *pci)
>  	disable_irq(pcie_ep->perst_irq);
>  }
>  
> +static void qcom_pcie_dbi_cs2_access(struct dw_pcie *pci, bool enable)
> +{
> +	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> +
> +	writel_relaxed(enable, pcie_ep->elbi + ELBI_CS2_ENABLE);

Don't you want to maintain the ordering of whatever write came before
this?

Regards,
Bjorn

> +	/*
> +	 * Do a dummy read to make sure that the previous write has reached the
> +	 * memory before returning.
> +	 */
> +	readl_relaxed(pcie_ep->elbi + ELBI_CS2_ENABLE);
> +}
> +
>  static void qcom_pcie_ep_icc_update(struct qcom_pcie_ep *pcie_ep)
>  {
>  	struct dw_pcie *pci = &pcie_ep->pci;
> @@ -500,6 +513,7 @@ static const struct dw_pcie_ops pci_ops = {
>  	.link_up = qcom_pcie_dw_link_up,
>  	.start_link = qcom_pcie_dw_start_link,
>  	.stop_link = qcom_pcie_dw_stop_link,
> +	.dbi_cs2_access = qcom_pcie_dbi_cs2_access,
>  };
>  
>  static int qcom_pcie_ep_get_io_resources(struct platform_device *pdev,
> 
> -- 
> 2.25.1
>