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Message-ID: <20250820214010.GA641668@bhelgaas>
Date: Wed, 20 Aug 2025 16:40:10 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Richard Zhu <hongxing.zhu@....com>
Cc: frank.li@....com, l.stach@...gutronix.de, lpieralisi@...nel.org,
kwilczynski@...nel.org, mani@...nel.org, robh@...nel.org,
bhelgaas@...gle.com, shawnguo@...nel.org, s.hauer@...gutronix.de,
kernel@...gutronix.de, festevam@...il.com,
linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
imx@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] PCI: imx6: Add a method to handle CLKREQ#
override active low
On Wed, Aug 20, 2025 at 04:10:48PM +0800, Richard Zhu wrote:
> The CLKREQ# is an open drain, active low signal that is driven low by
> the card to request reference clock.
>
> Since the reference clock may be required by i.MX PCIe host too. To make
> sure this clock is available even when the CLKREQ# isn't driven low by
> the card(e.x no card connected), force CLKREQ# override active low for
> i.MX PCIe host during initialization.
>
> The CLKREQ# override can be cleared safely when supports-clkreq is
> present and PCIe link is up later. Because the CLKREQ# would be driven
> low by the card in this case.
>
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> ---
> drivers/pci/controller/dwc/pci-imx6.c | 35 +++++++++++++++++++++++++++
> 1 file changed, 35 insertions(+)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 80e48746bbaf6..a73632b47e2d3 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -52,6 +52,8 @@
> #define IMX95_PCIE_REF_CLKEN BIT(23)
> #define IMX95_PCIE_PHY_CR_PARA_SEL BIT(9)
> #define IMX95_PCIE_SS_RW_REG_1 0xf4
> +#define IMX95_PCIE_CLKREQ_OVERRIDE_EN BIT(8)
> +#define IMX95_PCIE_CLKREQ_OVERRIDE_VAL BIT(9)
> #define IMX95_PCIE_SYS_AUX_PWR_DET BIT(31)
>
> #define IMX95_PE0_GEN_CTRL_1 0x1050
> @@ -136,6 +138,7 @@ struct imx_pcie_drvdata {
> int (*enable_ref_clk)(struct imx_pcie *pcie, bool enable);
> int (*core_reset)(struct imx_pcie *pcie, bool assert);
> int (*wait_pll_lock)(struct imx_pcie *pcie);
> + void (*clr_clkreq_override)(struct imx_pcie *pcie);
> const struct dw_pcie_host_ops *ops;
> };
>
> @@ -149,6 +152,7 @@ struct imx_pcie {
> struct gpio_desc *reset_gpiod;
> struct clk_bulk_data *clks;
> int num_clks;
> + bool supports_clkreq;
> struct regmap *iomuxc_gpr;
> u16 msi_ctrl;
> u32 controller_id;
> @@ -267,6 +271,13 @@ static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
> IMX95_PCIE_REF_CLKEN,
> IMX95_PCIE_REF_CLKEN);
>
> + /* Force CLKREQ# low by override */
> + regmap_update_bits(imx_pcie->iomuxc_gpr,
> + IMX95_PCIE_SS_RW_REG_1,
> + IMX95_PCIE_CLKREQ_OVERRIDE_EN |
> + IMX95_PCIE_CLKREQ_OVERRIDE_VAL,
> + IMX95_PCIE_CLKREQ_OVERRIDE_EN |
> + IMX95_PCIE_CLKREQ_OVERRIDE_VAL);
> return 0;
> }
>
> @@ -1298,6 +1309,18 @@ static void imx_pcie_host_exit(struct dw_pcie_rp *pp)
> regulator_disable(imx_pcie->vpcie);
> }
>
> +static void imx8mm_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
> +{
> + imx8mm_pcie_enable_ref_clk(imx_pcie, false);
> +}
> +
> +static void imx95_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
> +{
> + regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
> + IMX95_PCIE_CLKREQ_OVERRIDE_EN |
> + IMX95_PCIE_CLKREQ_OVERRIDE_VAL, 0);
> +}
> +
> static void imx_pcie_host_post_init(struct dw_pcie_rp *pp)
> {
> struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> @@ -1322,6 +1345,12 @@ static void imx_pcie_host_post_init(struct dw_pcie_rp *pp)
> dw_pcie_writel_dbi(pci, GEN3_RELATED_OFF, val);
> dw_pcie_dbi_ro_wr_dis(pci);
> }
> +
> + /* Clear CLKREQ# override if supports_clkreq is true and link is up */
> + if (dw_pcie_link_up(pci) && imx_pcie->supports_clkreq) {
> + if (imx_pcie->drvdata->clr_clkreq_override)
> + imx_pcie->drvdata->clr_clkreq_override(imx_pcie);
> + }
> }
>
> /*
> @@ -1745,6 +1774,8 @@ static int imx_pcie_probe(struct platform_device *pdev)
> pci->max_link_speed = 1;
> of_property_read_u32(node, "fsl,max-link-speed", &pci->max_link_speed);
>
> + imx_pcie->supports_clkreq =
> + of_property_read_bool(node, "supports-clkreq");
Is there a DT binding update that goes along with this? I see
"supports-clkreq" mentioned in
Documentation/devicetree/bindings/pci/nvidia,tegra194-pcie.yaml, but
nowhere else.
Should this be some kind of generic thing? CLKREQ# itself is part of
the PCIe base spec, so it's definitely not device-specific.
But I'm not sure what this property is telling us. Based on the
patch:
- We assert CLKREQ# on IMX95 (and on IMX95_EP, which seems sort of
weird) regardless of "supports-clkreq".
- We call .clr_clkreq_override() to stop asserting CLKREQ# on
IMX8MQ, IMX8MM, IMX8MP, and IMX95 (but not IMX95_EP), but only if
they have "supports-clkreq" in devicetree.
So I don't know whether or how CLKREQ# is asserted on IMX8MQ, IMX8MM,
and IMX8MP.
And I don't know why we assert CLKREQ# on IMX95_EP but apparently
never stop asserting it.
And I don't know why we assert CLKREQ# regardless of "supports-clkreq"
but only stop asserting it if "supports-clkreq" is present.
> imx_pcie->vpcie = devm_regulator_get_optional(&pdev->dev, "vpcie");
> if (IS_ERR(imx_pcie->vpcie)) {
> if (PTR_ERR(imx_pcie->vpcie) != -ENODEV)
> @@ -1873,6 +1904,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
> .mode_mask[1] = IMX8MQ_GPR12_PCIE2_CTRL_DEVICE_TYPE,
> .init_phy = imx8mq_pcie_init_phy,
> .enable_ref_clk = imx8mm_pcie_enable_ref_clk,
> + .clr_clkreq_override = imx8mm_pcie_clr_clkreq_override,
> },
> [IMX8MM] = {
> .variant = IMX8MM,
> @@ -1883,6 +1915,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
> .mode_off[0] = IOMUXC_GPR12,
> .mode_mask[0] = IMX6Q_GPR12_DEVICE_TYPE,
> .enable_ref_clk = imx8mm_pcie_enable_ref_clk,
> + .clr_clkreq_override = imx8mm_pcie_clr_clkreq_override,
> },
> [IMX8MP] = {
> .variant = IMX8MP,
> @@ -1893,6 +1926,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
> .mode_off[0] = IOMUXC_GPR12,
> .mode_mask[0] = IMX6Q_GPR12_DEVICE_TYPE,
> .enable_ref_clk = imx8mm_pcie_enable_ref_clk,
> + .clr_clkreq_override = imx8mm_pcie_clr_clkreq_override,
> },
> [IMX8Q] = {
> .variant = IMX8Q,
> @@ -1913,6 +1947,7 @@ static const struct imx_pcie_drvdata drvdata[] = {
> .core_reset = imx95_pcie_core_reset,
> .init_phy = imx95_pcie_init_phy,
> .wait_pll_lock = imx95_pcie_wait_for_phy_pll_lock,
> + .clr_clkreq_override = imx95_pcie_clr_clkreq_override,
> },
> [IMX8MQ_EP] = {
> .variant = IMX8MQ_EP,
> --
> 2.37.1
>
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