Re: [PATCH 3/4] PCI: dra7xx: Add support to force RC to work in GEN1 mode

[Bjorn Helgaas <helgaas@kernel.org>]

Hi Kishon,

On Tue, Oct 11, 2016 at 06:28:34PM +0530, Kishon Vijay Abraham I wrote:
> PCIe in AM57x/DRA7x devices is by default
> configured to work in GEN2 mode.  However there
> may be situations when working in GEN1 mode is
> desired. One example is limitation i925 (PCIe GEN2
> mode not supported at junction temperatures < 0C).
> 
> Add support to force Root Complex to work in GEN1
> mode if so desired, but don't force GEN1 mode on
> any board just yet.
> 
> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
> Signed-off-by: Sekhar Nori <nsekhar@ti.com>
> ---
>  Documentation/devicetree/bindings/pci/ti-pci.txt |    1 +
>  drivers/pci/host/pci-dra7xx.c                    |   27 ++++++++++++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/ti-pci.txt b/Documentation/devicetree/bindings/pci/ti-pci.txt
> index 60e2516..a3d6ca3 100644
> --- a/Documentation/devicetree/bindings/pci/ti-pci.txt
> +++ b/Documentation/devicetree/bindings/pci/ti-pci.txt
> @@ -25,6 +25,7 @@ PCIe Designware Controller
>  
>  Optional Property:
>   - gpios : Should be added if a gpio line is required to drive PERST# line
> + - ti,pcie-is-gen1 : Force the PCIe controller to work in GEN1 (2.5 GT/s).

Can we use "max-link-speed" so it's similar to imx6?

>  Example:
>  axi {
> diff --git a/drivers/pci/host/pci-dra7xx.c b/drivers/pci/host/pci-dra7xx.c
> index 4ccba6d..2a669cb 100644
> --- a/drivers/pci/host/pci-dra7xx.c
> +++ b/drivers/pci/host/pci-dra7xx.c
> @@ -63,11 +63,14 @@
>  #define	LINK_UP						BIT(16)
>  #define	DRA7XX_CPU_TO_BUS_ADDR				0x0FFFFFFF
>  
> +#define EXP_CAP_ID_OFFSET				0x70
> +
>  struct dra7xx_pcie {
>  	struct pcie_port	pp;
>  	void __iomem		*base;		/* DT ti_conf */
>  	int			phy_count;	/* DT phy-names count */
>  	struct phy		**phy;
> +	bool			is_gen1;
>  };
>  
>  #define to_dra7xx_pcie(x)	container_of((x), struct dra7xx_pcie, pp)
> @@ -96,12 +99,33 @@ static int dra7xx_pcie_establish_link(struct dra7xx_pcie *dra7xx_pcie)
>  	struct pcie_port *pp = &dra7xx_pcie->pp;
>  	struct device *dev = pp->dev;
>  	u32 reg;
> +	u32 exp_cap_off = EXP_CAP_ID_OFFSET;
>  
>  	if (dw_pcie_link_up(pp)) {
>  		dev_err(dev, "link is already up\n");
>  		return 0;
>  	}
>  
> +	if (dra7xx_pcie->is_gen1) {
> +		dw_pcie_cfg_read(pp->dbi_base + exp_cap_off + PCI_EXP_LNKCAP,
> +				 4, &reg);
> +		if ((reg & PCI_EXP_LNKCAP_SLS) != PCI_EXP_LNKCAP_SLS_2_5GB) {
> +			reg &= ~((u32)PCI_EXP_LNKCAP_SLS);
> +			reg |= PCI_EXP_LNKCAP_SLS_2_5GB;
> +			dw_pcie_cfg_write(pp->dbi_base + exp_cap_off +
> +					  PCI_EXP_LNKCAP, 4, reg);
> +		}
> +
> +		dw_pcie_cfg_read(pp->dbi_base + exp_cap_off + PCI_EXP_LNKCTL2,
> +				 2, &reg);
> +		if ((reg & PCI_EXP_LNKCAP_SLS) != PCI_EXP_LNKCAP_SLS_2_5GB) {
> +			reg &= ~((u32)PCI_EXP_LNKCAP_SLS);
> +			reg |= PCI_EXP_LNKCAP_SLS_2_5GB;
> +			dw_pcie_cfg_write(pp->dbi_base + exp_cap_off +
> +					  PCI_EXP_LNKCTL2, 2, reg);
> +		}
> +	}
> +
>  	reg = dra7xx_pcie_readl(dra7xx_pcie, PCIECTRL_DRA7XX_CONF_DEVICE_CMD);
>  	reg |= LTSSM_EN;
>  	dra7xx_pcie_writel(dra7xx_pcie, PCIECTRL_DRA7XX_CONF_DEVICE_CMD, reg);
> @@ -402,6 +426,9 @@ static int __init dra7xx_pcie_probe(struct platform_device *pdev)
>  	reg &= ~LTSSM_EN;
>  	dra7xx_pcie_writel(dra7xx_pcie, PCIECTRL_DRA7XX_CONF_DEVICE_CMD, reg);
>  
> +	if (of_property_read_bool(np, "ti,pcie-is-gen1"))
> +		dra7xx_pcie->is_gen1 = true;
> +
>  	ret = dra7xx_add_pcie_port(dra7xx_pcie, pdev);
>  	if (ret < 0)
>  		goto err_gpio;
> -- 
> 1.7.9.5
>