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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 > > --- > > 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); > > It seems racy to clear the override when the link is up. > > Since it sounds like the i.MX host requires refclock all the time, why > not keep the override permanently? It will Lost l1ss support if enable override permanetly. I think other platform have similar issues (at least dwc controller). Most platform use m.2 socket, which pull down clk_req by EP side devices. Only standard PCIe slots, which clkreq have not connect by EP devices because stardard PCIe slots add #clkreq signal happen recent years (maybe after miniPCIe slot spec). Some old PCIe devices have not connect it. Even latest PCIe devices, I saw have jumper in PCIe card to controller #clkreq. > > Obviously it must be ok to keep the override for a while, because > there is some interval between the link coming up and the call of > .clr_clkreq_override(). > > Would something bad happen if we *never* called > .clr_clkreq_override()? clock will always running, lost L1SS power save feature. Frank > > Bjorn