linux-kernel - Re: [PATCH v5 4/4] PCI: qcom: Switch pcie_1_pipe_clk

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Date:   Tue, 31 Aug 2021 12:07:30 +0530
From:   Prasad Malisetty <pmaliset@...eaurora.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>, agross@...nel.org,
        bhelgaas@...gle.com, bjorn.andersson@...aro.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,
        dianders@...omium.org, mka@...omium.org, vbadigan@...eaurora.org,
        sallenki@...eaurora.org, manivannan.sadhasivam@...aro.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH v5 4/4] PCI: qcom: Switch pcie_1_pipe_clk_src after PHY
 init in SC7280

On 2021-08-26 18:07, Rob Herring wrote:
> On Thu, Aug 26, 2021 at 2:22 AM Prasad Malisetty
> <pmaliset@...eaurora.org> wrote:
>> 
>> On 2021-08-26 02:55, Bjorn Helgaas wrote:
>> > [+cc linux-pci; patches to drivers/pci/ should always be cc'd there]
>> >
>> > On Wed, Aug 25, 2021 at 07:30:09PM +0000, Stephen Boyd wrote:
>> >> Quoting Prasad Malisetty (2021-08-24 01:10:48)
>> >> > On 2021-08-17 22:56, Prasad Malisetty wrote:
>> >> > > On 2021-08-10 09:38, Prasad Malisetty wrote:
>> >> > >> 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@...eaurora.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
>> >> > >> @@ -166,6 +166,8 @@ struct qcom_pcie_resources_2_7_0 {
>> >> > >>      struct regulator_bulk_data supplies[2];
>> >> > >>      struct reset_control *pci_reset;
>> >> > >>      struct clk *pipe_clk;
>> >> > >> +    struct clk *gcc_pcie_1_pipe_clk_src;
>> >> > >> +    struct clk *phy_pipe_clk;
>> >> > >>  };
>> >> > >>
>> >> > >>  union qcom_pcie_resources {
>> >> > >> @@ -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);
>> >> > >> +    }
>> >> > >
>> >> > > I would like to check is there any other better approach instead of
>> >> > > compatible method here as well or is it fine to use compatible method.
>> >>
>> >> I'd prefer the compatible method. If nobody is responding then it's
>> >> best
>> >> to just resend the patches with the approach you prefer instead of
>> >> waiting for someone to respond to a review comment.
>> >
>> > I'm missing some context here, so I'm not exactly sure what your
>> > question is, Prasad, but IMO drivers generally should not need to use
>> > of_device_is_compatible() if they've already called
>> > of_device_get_match_data() (as qcom_pcie_probe() has).
>> >
>> > of_device_is_compatible() does basically the same work of looking for
>> > a match in qcom_pcie_match[] that of_device_get_match_data() does, so
>> > it seems pointless to repeat it.
> 
> +1
> 
>> > I am a little confused because while [1] adds "qcom,pcie-sc7280" to
>> > qcom,pcie.txt, I don't see a patch that adds it to qcom_pcie_match[].
> 
> Either that's missing or there's a fallback to 8250 that's not 
> documented.
>> >
>> > Bjorn
>> >
>> Hi Bjorn,
>> 
>> I agree on your point, but the main reason is to use compatible in
>> get_resources_2_7_0 is same hardware version. For SM8250 & SC7280
>> platforms, the hw version is same. Since we can't have a separate ops
>> for SC7280, we are using compatible method in get_resources_2_7_0 to
>> differentiate SM8250 and SC7280.
> 
> Then fix the match data to be not just ops, but ops and the flag you 
> need here.
> 
> Rob

Hi Rob,

Thanks for your review comments and inputs .

This difference is not universal across all the platforms but instead 
this is specific to SC7280.
Hence it make sense to use compatible other than going for a flag.

Thanks
-Prasad