[PATCH v3 2/2] PCI: imx6: Add a method to handle CLKREQ# override active low

[Hongxing Zhu]

> -----Original Message-----
> From: Manivannan Sadhasivam <mani at kernel.org>
> Sent: 2025年9月22日 14:13
> To: Hongxing Zhu <hongxing.zhu at nxp.com>
> Cc: Frank Li <frank.li at nxp.com>; jingoohan1 at gmail.com;
> l.stach at pengutronix.de; lpieralisi at kernel.org; kwilczynski at kernel.org;
> robh at kernel.org; bhelgaas at google.com; shawnguo at kernel.org;
> s.hauer at pengutronix.de; kernel at pengutronix.de; festevam at gmail.com;
> linux-pci at vger.kernel.org; linux-arm-kernel at lists.infradead.org;
> imx at lists.linux.dev; linux-kernel at vger.kernel.org
> Subject: Re: [PATCH v3 2/2] PCI: imx6: Add a method to handle CLKREQ#
> override active low
> 
> On Mon, Sep 22, 2025 at 10:37:41AM +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.
> >
> > Signed-off-by: Richard Zhu <hongxing.zhu at nxp.com>
> > Reviewed-by: Frank Li <Frank.Li at nxp.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 80e48746bbaf..a73632b47e2d 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);
> 
> This should be:
> 
> 	imx95_pcie_clkreq_override(imx_pcie, true);
> 
> refer below...
> 
> >  	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);
> 
> Just noticed this discrepancy. 'imx8mm_pcie_enable_ref_clk(, false)' is
> enabling the CLKREQ# override, thereby enabling the refclk. But only for
> imx8mm, this helper is called as imx8mm_pcie_enable_ref_clk(). But for
> imx95, the equivalent function is called as imx95_pcie_clr_clkreq_override().
> This is causing confusion.
> 
> Maybe you should just call both functions as:
> 
> 	imx8mm_pcie_clkreq_override(imx_pcie, bool enable);
> 	imx95_pcie_clkreq_override(imx_pcie, bool enable);
> 
> Then,
> 
> 	imx8mm_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
> 	{
> 		imx8mm_pcie_clkreq_override(imx_pcie, false)
> 	}
> 
> 	imx95_pcie_clr_clkreq_override(struct imx_pcie *imx_pcie)
> 	{
> 		imx95_pcie_clkreq_override(imx_pcie, false)
> 	}
> 
> and populate the clr_clkreq_override() callback.
Good proposal, let me clean up codes as this.
Thanks.

Best Regards
Richard Zhu
> 
> - Mani
> 
> --
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