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Date: Mon, 09 Aug 2021 22:39:30 +0530
From: Prasad Malisetty <pmaliset@...eaurora.org>
To: Bjorn Andersson <bjorn.andersson@...aro.org>
Cc: Bjorn Helgaas <helgaas@...nel.org>, 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,
dianders@...omium.org, mka@...omium.org, vbadigan@...eaurora.org,
sallenki@...eaurora.org
Subject: Re: [PATCH v4 4/4] PCIe: qcom: Add support to control pipe clk src
On 2021-07-17 02:08, Bjorn Andersson wrote:
> On Fri 16 Jul 10:06 CDT 2021, Bjorn Helgaas wrote:
>
>> Run this:
>>
>> $ git log --oneline drivers/pci/controller/dwc/pcie-qcom.c
>>
>> and make your subject match the style and structure (in particular,
>> s/PCIe/PCI/). In this case, maybe something like this?
>>
>> PCI: qcom: Switch sc7280 gcc_pcie_1_pipe_clk_src after PHY init
>>
>> On Fri, Jul 16, 2021 at 07:28:47PM +0530, Prasad Malisetty wrote:
>> > This is a new requirement for sc7280 SoC.
>> > To enable gdsc gcc_pcie_1_pipe_clk_src should be TCXO.
>> > after PHY initialization gcc_pcie_1_pipe_clk_src needs
>> > to switch from TCXO to gcc_pcie_1_pipe_clk.
>>
>> This says what *needs* to happen, but it doesn't actually say what
>> this patch *does*. I think it's something like:
>>
>> On the sc7280 SoC, the clock source for pcie_1_pipe must be the TCXO
>> while gdsc is enabled. But after the PHY is initialized, the clock
>> source must be switched to gcc_pcie_1_pipe_clk.
>>
>> On sc7280, switch gcc_pcie_1_pipe_clk_src from TCXO to
>> gcc_pcie_1_pipe_clk after the PHY has been initialized.
>>
>> Nits: Rewrap to fill 75 columns or so. Add blank lines between
>> paragraphs. Start sentences with capital letter.
>>
>> > 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..9e0e4ab 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 *gcc_pcie_1_pipe_clk_src;
>> > + struct clk *phy_pipe_clk;
>> > + 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->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->ref_clk_src = devm_clk_get(dev, "ref");
>> > + if (IS_ERR(res->ref_clk_src))
>> > + return PTR_ERR(res->ref_clk_src);
>>
>> Not clear why ref_clk_src is here, since it's not used anywhere. If
>> it's not necessary here, drop it and add it in a future patch that
>> uses it.
>>
>> > + }
>> > +
>> > 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"))
>>
>> Using of_device_is_compatible() follows existing style in the driver,
>> which is good. But I'm not sure that's good style in general because
>> it's a little repetitious and wasteful.
>>
>
> Following the style is good, but up until the recent sm8250 addition it
> was just a hack to deal with legacy platforms that we don't know the
> exact details about.
>
> But, all platforms I know of has the pipe_clk from the PHY fed into the
> pipe_clk_src mux in the gcc block and then ends up in the PCIe
> controller. As such, I suspect that the pipe_clk handling should be
> moved
> to the common code path of the driver and there's definitely no harm in
> making sure that the pipe_clk_src mux is explicitly configured on
> existing platforms (at least all 2.7.0 based ones).
>
>> qcom_pcie_probe() already calls of_device_get_match_data(), which does
>> basically the same thing as of_device_is_compatible(), so I think we
>> could take better advantage of that by augmenting struct qcom_pcie_ops
>> with these device-specific details.
>>
>
> I agree.
>
> Regards,
> Bjorn
>
>> Some drivers that use this strategy:
>>
>> drivers/pci/controller/cadence/pci-j721e.c
>> drivers/pci/controller/dwc/pci-imx6.c
>> drivers/pci/controller/dwc/pci-layerscape.c
>> drivers/pci/controller/dwc/pci-layerscape-ep.c
>> drivers/pci/controller/dwc/pcie-tegra194.c
>> drivers/pci/controller/pci-ftpci100.c
>> drivers/pci/controller/pcie-brcmstb.c
>> drivers/pci/controller/pcie-mediatek.c
>>
>> > + clk_set_parent(res->gcc_pcie_1_pipe_clk_src, res->phy_pipe_clk);
>> >
>> > return clk_prepare_enable(res->pipe_clk);
>> > }
>> > --
Hi Bjorn,
Thanks for your review and inputs.
I would like to add more details on this requirement. The hardware ver.
of SM8250 & SC7280 platforms is the same but
where as only for SC7280, we need to switch gcc_pcie_1_pipe_clk source
between TXCO and gcc_pcie_1_pipe_clk hence this is SoC level
specific requirement. all existing platforms doesn't need this pipe clk
handling.
I will use boolean flag entry in SoC dtsi such as
"pipe-clk-source-switch" to differentiate between SM8250 and SC7280
instead of compatible
method.
Please provide any other better approach for the above case.
Thanks
-Prasad
>> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> > a Linux Foundation Collaborative Project
>> >
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