Re: [PATCH v2 3/3] PCI: imx: Add workaround for e10728, IMX7d PCIe PLL failure

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Tue, Feb 05, 2019 at 12:17:41AM +0000, Trent Piepho wrote:
> This implements the workound described in the NXP IMX7d erratum e10728.
> 
> Initial VCO oscillation may fail under corner conditions such as cold
> temperature.  It causes PCIe PLL to fail to lock in the initialization
> phase, which results in the PCIe link failing to come up.
> 
> The workaround is to disable Duty-cycle Corrector (DCC) calibration
> after G_RST.
> 
> To do this it is necessary to gain access to the undocumented and
> currently unused PCIe PHY register bank.  A new device tree node of type
> "fsl,imx7d-pcie-phy" is created for the PHY block and the existing PCIe
> device uses a phandle named "fsl,imx7d-pcie-phy" to point to it.
> 
> Signed-off-by: Trent Piepho <tpiepho@impinj.com>
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 57 +++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 80f843030e36..06dd6aa927d4 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -18,6 +18,7 @@
>  #include <linux/module.h>
>  #include <linux/of_gpio.h>
>  #include <linux/of_device.h>
> +#include <linux/of_address.h>
>  #include <linux/pci.h>
>  #include <linux/platform_device.h>
>  #include <linux/regmap.h>
> @@ -61,6 +62,7 @@ struct imx6_pcie {
>  	u32			tx_swing_low;
>  	int			link_gen;
>  	struct regulator	*vpcie;
> +	void __iomem		*phy_base;
>  
>  	/* power domain for pcie */
>  	struct device		*pd_pcie;
> @@ -117,6 +119,23 @@ struct imx6_pcie {
>  #define PCIE_PHY_RX_ASIC_OUT 0x100D
>  #define PCIE_PHY_RX_ASIC_OUT_VALID	(1 << 0)
>  
> +/* iMX7 PCIe PHY registers */
> +#define PCIE_PHY_CMN_REG4		0x14
> +/* These are probably the bits that *aren't* DCC_FB_EN */
> +#define PCIE_PHY_CMN_REG4_DCC_FB_EN	0x29
> +
> +#define PCIE_PHY_CMN_REG15	        0x54
> +#define PCIE_PHY_CMN_REG15_DLY_4	BIT(2)
> +#define PCIE_PHY_CMN_REG15_PLL_PD	BIT(5)
> +#define PCIE_PHY_CMN_REG15_OVRD_PLL_PD	BIT(7)
> +
> +#define PCIE_PHY_CMN_REG24		0x90
> +#define PCIE_PHY_CMN_REG24_RX_EQ	BIT(6)
> +#define PCIE_PHY_CMN_REG24_RX_EQ_SEL	BIT(3)
> +
> +#define PCIE_PHY_CMN_REG26		0x98
> +#define PCIE_PHY_CMN_REG26_ATT_MODE	0xBC
> +
>  #define PHY_RX_OVRD_IN_LO 0x1005
>  #define PHY_RX_OVRD_IN_LO_RX_DATA_EN (1 << 5)
>  #define PHY_RX_OVRD_IN_LO_RX_PLL_EN (1 << 3)
> @@ -490,6 +509,26 @@ static void imx6_pcie_deassert_core_reset(struct imx6_pcie *imx6_pcie)
>  	switch (imx6_pcie->variant) {
>  	case IMX7D:
>  		reset_control_deassert(imx6_pcie->pciephy_reset);
> +
> +		/* Workaround for ERR010728, failure of PCI-e PLL VCO to
> +		 * oscillate, especially when cold.  This turns off "Duty-cycle
> +		 * Corrector" and other mysterious undocumented things.
> +		 */
> +		if (likely(imx6_pcie->phy_base)) {

Nit: this is not a fast-path, so this branch performance is hardly
relevant.

> +			/* De-assert DCC_FB_EN */
> +			writel(PCIE_PHY_CMN_REG4_DCC_FB_EN,
> +			       imx6_pcie->phy_base + PCIE_PHY_CMN_REG4);
> +			/* Assert RX_EQS and RX_EQS_SEL */
> +			writel(PCIE_PHY_CMN_REG24_RX_EQ_SEL
> +				| PCIE_PHY_CMN_REG24_RX_EQ,
> +			       imx6_pcie->phy_base + PCIE_PHY_CMN_REG24);
> +			/* Assert ATT_MODE */
> +			writel(PCIE_PHY_CMN_REG26_ATT_MODE,
> +			       imx6_pcie->phy_base + PCIE_PHY_CMN_REG26);
> +		} else {
> +			dev_warn(dev, "DT lacks imx7d-pcie-phy, unable to apply ERR010728 workaround\n");

It is a nit but the warning log is not necessarily true ie you may not
have a mapped address for other reasons as well. It is up to you but I
would change the log message.

Thanks,
Lorenzo

> +		}
> +
>  		imx7d_pcie_wait_for_phy_pll_lock(imx6_pcie);
>  		break;
>  	case IMX6SX:
> @@ -919,6 +958,7 @@ static int imx6_pcie_probe(struct platform_device *pdev)
>  	struct device *dev = &pdev->dev;
>  	struct dw_pcie *pci;
>  	struct imx6_pcie *imx6_pcie;
> +	struct device_node *np;
>  	struct resource *dbi_base;
>  	struct device_node *node = dev->of_node;
>  	int ret;
> @@ -939,6 +979,23 @@ static int imx6_pcie_probe(struct platform_device *pdev)
>  	imx6_pcie->variant =
>  		(enum imx6_pcie_variants)of_device_get_match_data(dev);
>  
> +	/* Find the PHY if one is defined, only imx7d uses it */
> +	np = of_parse_phandle(node, "fsl,imx7d-pcie-phy", 0);
> +	if (np) {
> +		struct resource res;
> +
> +		ret = of_address_to_resource(np, 0, &res);
> +		if (ret) {
> +			dev_err(dev, "Unable to map PCIe PHY\n");
> +			return ret;
> +		}
> +		imx6_pcie->phy_base = devm_ioremap_resource(dev, &res);
> +		if (IS_ERR(imx6_pcie->phy_base)) {
> +			dev_err(dev, "Unable to map PCIe PHY\n");
> +			return PTR_ERR(imx6_pcie->phy_base);
> +		}
> +	}
> +
>  	dbi_base = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>  	pci->dbi_base = devm_ioremap_resource(dev, dbi_base);
>  	if (IS_ERR(pci->dbi_base))
> -- 
> 2.14.4
> 

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