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Date:   Mon, 09 Aug 2021 22:39:30 +0530
From:   Prasad Malisetty <pmaliset@codeaurora.org>
To:     Bjorn Andersson <bjorn.andersson@linaro.org>
Cc:     Bjorn Helgaas <helgaas@kernel.org>, agross@kernel.org,
        bhelgaas@google.com, robh+dt@kernel.org, swboyd@chromium.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
Subject: Re: [PATCH v4 4/4] PCIe: qcom: Add support to control pipe clk src
In-Reply-To: <YPHuWudai/FO6SMN@yoga>
References: <1626443927-32028-5-git-send-email-pmaliset@codeaurora.org>
 <20210716150646.GA2098485@bjorn-Precision-5520> <YPHuWudai/FO6SMN@yoga>
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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@codeaurora.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

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