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Date:   Tue, 31 Aug 2021 10:37:14 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Prasad Malisetty <pmaliset@codeaurora.org>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Stephen Boyd <swboyd@chromium.org>, agross@kernel.org,
        bhelgaas@google.com, bjorn.andersson@linaro.org,
        lorenzo.pieralisi@arm.com, 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,
        linux-pci@vger.kernel.org
Subject: Re: [PATCH v5 4/4] PCI: qcom: Switch pcie_1_pipe_clk_src after PHY
 init in SC7280
Message-ID: <20210831153714.GA103513@bjorn-Precision-5520>
MIME-Version: 1.0
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In-Reply-To: <268d53aa6ec8f05928f083dfb0484ae2@codeaurora.org>
Precedence: bulk

On Tue, Aug 31, 2021 at 12:07:30PM +0530, Prasad Malisetty wrote:
> On 2021-08-26 18:07, Rob Herring wrote:
> > On Thu, Aug 26, 2021 at 2:22 AM Prasad Malisetty
> > <pmaliset@codeaurora.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@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
> > > >> > >> @@ -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.
> >
> > > 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.
> 
> 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.

There's no reason your qcom_pcie_match[].data pointers need to be
strictly based on the hardware version.

You can do something like what pcie-brcmstb.c does, e.g.,

  struct pcie_cfg_data {
    struct qcom_pcie_ops *ops;
    unsigned int pipe_mux:1;
  };

  static const struct pcie_cfg_data sm8250_cfg = {
    .ops = &ops_1_9_0,
  };

  static const struct pcie_cfg_data sc7280_cfg = {
    .ops = &ops_1_9_0,
    .pipe_mux = 1,
  };

  static const struct of_device_id qcom_pcie_match[] = {
    { .compatible = "qcom,pcie-sm8250", .data = &sm8250_cfg },
    { .compatible = "qcom,pcie-sc7280", .data = &sc7280_cfg },
  };