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Message-ID: <20250925220400.GA2206333@bhelgaas>
Date: Thu, 25 Sep 2025 17:04:00 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Richard Zhu <hongxing.zhu@....com>
Cc: frank.li@....com, jingoohan1@...il.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 v5 2/2] PCI: imx6: Add a method to handle CLKREQ#
override active low
On Tue, Sep 23, 2025 at 03:39:13PM +0800, Richard Zhu wrote:
> The CLKREQ# is an open drain, active low signal that is driven low by
> the card to request reference clock. It's an optional signal added in
> PCIe CEM r4.0, sec 2. Thus, this signal wouldn't be driven low if it's
> reserved.
>
> Since the reference clock controlled by CLKREQ# may be required by i.MX
> PCIe host too. To make sure this clock is ready even when the CLKREQ#
> isn't driven low by the card(e.x the scenario described above), 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 at this time.
What happens if we clear the CLKREQ# override (so the host doesn't
assert it), and the link is up but the card never asserts CLKREQ#
(since it's an optional signal)?
Does the i.MX host still work?
> Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> Reviewed-by: Frank Li <Frank.Li@....com>
> ---
> drivers/pci/controller/dwc/pci-imx6.c | 43 ++++++++++++++++++++++++++-
> 1 file changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 80e48746bbaf..6b03b1111d06 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;
> @@ -239,6 +243,16 @@ static unsigned int imx_pcie_grp_offset(const struct imx_pcie *imx_pcie)
> return imx_pcie->controller_id == 1 ? IOMUXC_GPR16 : IOMUXC_GPR14;
> }
>
> +static void imx95_pcie_clkreq_override(struct imx_pcie *imx_pcie, bool enable)
> +{
> + regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
> + IMX95_PCIE_CLKREQ_OVERRIDE_EN,
> + enable ? IMX95_PCIE_CLKREQ_OVERRIDE_EN : 0);
> + regmap_update_bits(imx_pcie->iomuxc_gpr, IMX95_PCIE_SS_RW_REG_1,
> + IMX95_PCIE_CLKREQ_OVERRIDE_VAL,
> + enable ? IMX95_PCIE_CLKREQ_OVERRIDE_VAL : 0);
> +}
> +
> static int imx95_pcie_init_phy(struct imx_pcie *imx_pcie)
> {
> /*
> @@ -685,7 +699,7 @@ static int imx6q_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
> return 0;
> }
>
> -static int imx8mm_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
> +static void imx8mm_pcie_clkreq_override(struct imx_pcie *imx_pcie, bool enable)
> {
> int offset = imx_pcie_grp_offset(imx_pcie);
>
> @@ -695,6 +709,11 @@ static int imx8mm_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
> regmap_update_bits(imx_pcie->iomuxc_gpr, offset,
> IMX8MQ_GPR_PCIE_CLK_REQ_OVERRIDE_EN,
> enable ? IMX8MQ_GPR_PCIE_CLK_REQ_OVERRIDE_EN : 0);
> +}
> +
> +static int imx8mm_pcie_enable_ref_clk(struct imx_pcie *imx_pcie, bool enable)
> +{
> + imx8mm_pcie_clkreq_override(imx_pcie, enable);
> return 0;
> }
>
> @@ -1298,6 +1317,16 @@ 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_clkreq_override(imx_pcie, false);
> +}
> +
> +static void imx95_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
> +{
> + imx95_pcie_clkreq_override(imx_pcie, false);
> +}
> +
> static void imx_pcie_host_post_init(struct dw_pcie_rp *pp)
> {
> struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> @@ -1322,6 +1351,12 @@ 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 +1780,8 @@ 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");
> 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 +1910,7 @@ 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 +1921,7 @@ 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 +1932,7 @@ 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 +1953,7 @@ 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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