Re: [PATCH v4 2/2] PCI: mediatek-gen3: Add support for restricting link width

Bjorn Helgaas
2024-11-06T01:24:40Z

On Mon, Nov 04, 2024 at 12:49:35PM +0100, AngeloGioacchino Del Regno wrote:
> Add support for restricting the port's link width by specifying
> the num-lanes devicetree property in the PCIe node.
>
> The setting is done in the GEN_SETTINGS register (in the driver
> named as PCIE_SETTING_REG), where each set bit in [11:8] activates
> a set of lanes (from bits 11 to 8 respectively, x16/x8/x4/x2).

I guess GEN_SETTINGS doesn't correspond to a register defined by the
PCIe spec, right? The only thing in the spec that looks similar is
the Target Link Width in the Device Control 3 register, but the bit
position doesn't look like this PCIE_SETTING_LINK_WIDTH mask:

> #define PCIE_SETTING_REG 0x80
> +#define PCIE_SETTING_LINK_WIDTH GENMASK(11, 8)
> #define PCIE_SETTING_GEN_SUPPORT GENMASK(14, 12)
> #define PCIE_PCI_IDS_1 0x9c
> #define PCI_CLASS(class) (class << 8)
> @@ -168,6 +169,7 @@ struct mtk_msi_set {
> * @clks: PCIe clocks
> * @num_clks: PCIe clocks count for this port
> * @max_link_speed: Maximum link speed (PCIe Gen) for this port
> + * @num_lanes: Number of PCIe lanes for this port
> * @irq: PCIe controller interrupt number
> * @saved_irq_state: IRQ enable state saved at suspend time
> * @irq_lock: lock protecting IRQ register access
> @@ -189,6 +191,7 @@ struct mtk_gen3_pcie {
> struct clk_bulk_data *clks;
> int num_clks;
> u8 max_link_speed;
> + u8 num_lanes;
>
> int irq;
> u32 saved_irq_state;
> @@ -401,6 +404,14 @@ static int mtk_pcie_startup_port(struct mtk_gen3_pcie *pcie)
> val |= FIELD_PREP(PCIE_SETTING_GEN_SUPPORT,
> GENMASK(pcie->max_link_speed - 2, 0));
> }
> + if (pcie->num_lanes) {
> + val &= ~PCIE_SETTING_LINK_WIDTH;
> +
> + /* Zero means one lane, each bit activates x2/x4/x8/x16 */
> + if (pcie->num_lanes > 1)
> + val |= FIELD_PREP(PCIE_SETTING_LINK_WIDTH,
> + GENMASK(fls(pcie->num_lanes >> 2), 0));
> + };
> writel_relaxed(val, pcie->base + PCIE_SETTING_REG);
>
> /* Set Link Control 2 (LNKCTL2) speed restriction, if any */
> @@ -838,6 +849,7 @@ static int mtk_pcie_parse_port(struct mtk_gen3_pcie *pcie)
> struct device *dev = pcie->dev;
> struct platform_device *pdev = to_platform_device(dev);
> struct resource *regs;
> + u32 num_lanes;
>
> regs = platform_get_resource_byname(pdev, IORESOURCE_MEM, "pcie-mac");
> if (!regs)
> @@ -883,6 +895,14 @@ static int mtk_pcie_parse_port(struct mtk_gen3_pcie *pcie)
> return pcie->num_clks;
> }
>
> + ret = of_property_read_u32(dev->of_node, "num-lanes", &num_lanes);
> + if (ret == 0) {
> + if (num_lanes == 0 || num_lanes > 16 || (num_lanes != 1 && num_lanes % 2))
> + dev_warn(dev, "Invalid num-lanes, using controller defaults\n");
> + else
> + pcie->num_lanes = num_lanes;
> + }
> +
> return 0;
> }
>
> --
> 2.46.1
>