Re: [PATCH v4 4/4] PCIe: qcom: Add support to control pipe clk src

From: Prasad Malisetty
Date: Tue Jul 20 2021 - 07:30:16 EST

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.

Agree, looks good. will add more details and update the commit message in next version.

> Signed-off-by: Prasad Malisetty <pmaliset@xxxxxxxxxxxxxx>
> ---
> 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.

Its more useful in suspend /resume patch set. as of now we will move to suspend/resume patch set.
> + }
> +
> 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.


Some drivers that use this strategy:


> + clk_set_parent(res->gcc_pcie_1_pipe_clk_src, res->phy_pipe_clk);
> return clk_prepare_enable(res->pipe_clk);
> }

Sure, we will make use of struct qcom_pcie_ops and add a new callback to configure pipe clk src.
In coming platforms, if the platform doesn't need to configure pipe clk src, it will return as callback not defined.

We will incorporate the changes in next release.

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