linux-kernel - Re: [PATCH v2 1/1] PCI: qcom-ep: Implement write_dbi2() callback for writing DBI2 registers properly

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Date:   Thu, 26 Oct 2023 17:56:32 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     jingoohan1@...il.com, gustavo.pimentel@...opsys.com,
        lpieralisi@...nel.org, robh@...nel.org, kw@...ux.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_bjorande@...cinc.com, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/1] PCI: qcom-ep: Implement write_dbi2() callback for
 writing DBI2 registers properly

On Wed, Oct 25, 2023 at 06:30:29PM +0530, Manivannan Sadhasivam wrote:
> DWC core driver exposes the write_dbi2() callback for writing to the DBI2
> registers in a vendor specific way. On the Qcom EP plaforms, DBI_CS2 bit in
> the ELBI region needs to be asserted before writing to any DBI2 registers
> and deasserted once done. So let's implement the callback for the Qcom PCIe
> EP driver so that the DBI2 writes are handled properly in the hardware.
> 
> Without this callback, DBI2 register writes like BAR size won't go through
> and as a result, the default BAR size is set for all BARs.
> 
> Cc: stable@...r.kernel.org # 5.16+
> Fixes: f55fee56a631 ("PCI: qcom-ep: Add Qualcomm PCIe Endpoint controller driver")
> Suggested-by: Serge Semin <fancer.lancer@...il.com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Reviewed-by: Serge Semin <fancer.lancer@...il.com>

+1 tiny note below

> ---
>  drivers/pci/controller/dwc/pcie-qcom-ep.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> index 32c8d9e37876..7da0599f70e7 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 +263,21 @@ static void qcom_pcie_dw_stop_link(struct dw_pcie *pci)
>  	disable_irq(pcie_ep->perst_irq);
>  }
>  

> +static void qcom_pcie_write_dbi2(struct dw_pcie *pci, void __iomem *base,

Just a general observation. I am not sure whether it's a local
convention or not, but it looks like the rest of the Qcom dw_pcie_ops
callbacks have the "qcom_pcie_dw_" prefix.

-Serge(y)

> +				 u32 reg, size_t size, u32 val)
> +{
> +	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> +	int ret;
> +
> +	writel(1, pcie_ep->elbi + ELBI_CS2_ENABLE);
> +
> +	ret = dw_pcie_write(pci->dbi_base2 + reg, size, val);
> +	if (ret)
> +		dev_err(pci->dev, "Failed to write DBI2 register (0x%x): %d\n", reg, ret);
> +
> +	writel(0, 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 +516,7 @@ 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,
> +	.write_dbi2 = qcom_pcie_write_dbi2,
>  };
>  
>  static int qcom_pcie_ep_get_io_resources(struct platform_device *pdev,
> -- 
> 2.25.1
>