linux-kernel - Re: [PATCH v2 3/4] PCIe: qcom: Add support to control pipe clk mux

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Date:   Sat, 5 Jun 2021 21:15:38 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Prasad Malisetty <pmaliset@...eaurora.org>
Cc:     agross@...nel.org, bhelgaas@...gle.com, robh+dt@...nel.org,
        swboyd@...omium.org, lorenzo.pieralisi@....com,
        svarbanov@...sol.com, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, mgautam@...eaurora.org,
        dianders@...omium.org, mka@...omium.org, sanm@...eaurora.org
Subject: Re: [PATCH v2 3/4] PCIe: qcom: Add support to control pipe clk mux

On Sat 05 Jun 09:40 CDT 2021, Prasad Malisetty wrote:

> In PCIe driver pipe-clk mux needs to switch between pipe_clk
> and XO for GDSC enable. This is done by setting pipe_clk mux
> as parent of pipe_clk after phy init.

But you're not switching between pipe_clk and XO, you're only making
sure that the pipe_clk is parented by the PHY's pipe clock.

Also, can you please elaborate on how this relates to the GDSC?

> 
> Signed-off-by: Prasad Malisetty <pmaliset@...eaurora.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 8a7a300..5cbbea4 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -166,6 +166,9 @@ struct qcom_pcie_resources_2_7_0 {
>  	struct regulator_bulk_data supplies[2];
>  	struct reset_control *pci_reset;
>  	struct clk *pipe_clk;
> +	struct clk *pipe_clk_mux;
> +	struct clk *pipe_ext_src;
> +	struct clk *ref_clk_src;
>  };
>  
>  union qcom_pcie_resources {
> @@ -1167,6 +1170,20 @@ static int qcom_pcie_get_resources_2_7_0(struct qcom_pcie *pcie)
>  	if (ret < 0)
>  		return ret;
>  
> +	if (of_device_is_compatible(dev->of_node, "qcom,pcie-sc7280")) {
> +		res->pipe_clk_mux = devm_clk_get(dev, "pipe_src");
> +		if (IS_ERR(res->pipe_clk_mux))
> +			return PTR_ERR(res->pipe_clk_mux);
> +
> +		res->pipe_ext_src = devm_clk_get(dev, "pipe_ext");
> +		if (IS_ERR(res->pipe_ext_src))
> +			return PTR_ERR(res->pipe_ext_src);
> +
> +		res->ref_clk_src = devm_clk_get(dev, "ref");
> +		if (IS_ERR(res->ref_clk_src))
> +			return PTR_ERR(res->ref_clk_src);
> +	}
> +
>  	res->pipe_clk = devm_clk_get(dev, "pipe");
>  	return PTR_ERR_OR_ZERO(res->pipe_clk);
>  }
> @@ -1255,6 +1272,11 @@ static void qcom_pcie_deinit_2_7_0(struct qcom_pcie *pcie)
>  static int qcom_pcie_post_init_2_7_0(struct qcom_pcie *pcie)
>  {
>  	struct qcom_pcie_resources_2_7_0 *res = &pcie->res.v2_7_0;
> +	struct dw_pcie *pci = pcie->pci;
> +	struct device *dev = pci->dev;
> +
> +	if (of_device_is_compatible(dev->of_node, "qcom,pcie-sc7280"))

If this is something only found on 7280, you need to document (in the
commit message at least) why this does not apply to other platforms with
this controller.

Thanks,
Bjorn

> +		clk_set_parent(res->pipe_clk_mux, res->pipe_ext_src);
>  
>  	return clk_prepare_enable(res->pipe_clk);
>  }
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>