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Date:   Tue, 17 Aug 2021 12:10:05 +0530
From:   Prasad Malisetty <pmaliset@codeaurora.org>
To:     Stephen Boyd <swboyd@chromium.org>
Cc:     agross@kernel.org, bhelgaas@google.com, bjorn.andersson@linaro.org,
        lorenzo.pieralisi@arm.com, robh+dt@kernel.org,
        svarbanov@mm-sol.com, devicetree@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org, dianders@chromium.org,
        mka@chromium.org, vbadigan@codeaurora.org, sallenki@codeaurora.org,
        manivannan.sadhasivam@linaro.org
Subject: Re: [PATCH v5 4/4] PCI: qcom: Switch pcie_1_pipe_clk_src after PHY
 init in SC7280
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On 2021-08-11 01:07, Stephen Boyd wrote:
> Quoting Prasad Malisetty (2021-08-09 21:08:36)
>> On the SC7280, By default the clock source for pcie_1_pipe is
>> TCXO for gdsc enable. But after the PHY is initialized, the clock
>> source must be switched to gcc_pcie_1_pipe_clk from TCXO.
>> 
>> Signed-off-by: Prasad Malisetty <pmaliset@codeaurora.org>
>> ---
>>  drivers/pci/controller/dwc/pcie-qcom.c | 18 ++++++++++++++++++
>>  1 file changed, 18 insertions(+)
>> 
>> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c 
>> b/drivers/pci/controller/dwc/pcie-qcom.c
>> index 8a7a300..39e3b21 100644
>> --- a/drivers/pci/controller/dwc/pcie-qcom.c
>> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
>> @@ -1167,6 +1169,16 @@ 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->gcc_pcie_1_pipe_clk_src = devm_clk_get(dev, 
>> "pipe_mux");
>> +               if (IS_ERR(res->gcc_pcie_1_pipe_clk_src))
>> +                       return PTR_ERR(res->gcc_pcie_1_pipe_clk_src);
>> +
>> +               res->phy_pipe_clk = devm_clk_get(dev, "phy_pipe");
>> +               if (IS_ERR(res->phy_pipe_clk))
>> +                       return PTR_ERR(res->phy_pipe_clk);
>> +       }
>> +
>>         res->pipe_clk = devm_clk_get(dev, "pipe");
>>         return PTR_ERR_OR_ZERO(res->pipe_clk);
>>  }
>> @@ -1255,6 +1267,12 @@ 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;
>> +       struct device_node *node = dev->of_node;
>> +
>> +       if (of_property_read_bool(node, "pipe-clk-source-switch"))
> 
> This can be straightline code. If gcc_pcie_1_pipe_clk_src is NULL,
> calling clk_set_parent() on it is a nop, return 0, so drop the property
> check and only assign the clk pointer if it needs to be done.
> 
>> +               clk_set_parent(res->gcc_pcie_1_pipe_clk_src, 
>> res->phy_pipe_clk);
> 
> Please check the return value and fail if it fails to set the parent.
> I'd also prefer a comment indicating that we have to set the parent
> because the GDSC must be enabled with the clk at XO speed. The DT 
> should
> probably also have an assigned clock parent of XO so when the driver
> probes it is set to XO parent for gdsc enable and then this driver code
> can change the parent to the phy pipe clk.
> 
>> 
>>         return clk_prepare_enable(res->pipe_clk);
>>  }

Hi Stephen,

Thanks for your review and inputs.

Yes, clk_set_parent function returning NULL if src pointer is NULL. we 
can call clk_set_parent function without any check.

I will validate and incorporate the changes in next version.

Thanks
-Prasad