linux-kernel - Re: [PATCH v3 2/2] PCI: mediatek-gen3: Add support for restricting link width

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Message-ID: <9e56fbe0b1a388b4e0da20cca53e157f51288916.camel@mediatek.com>
Date: Mon, 4 Nov 2024 08:56:53 +0000
From: Jianjun Wang (王建军) <Jianjun.Wang@...iatek.com>
To: "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>, "AngeloGioacchino
 Del Regno" <angelogioacchino.delregno@...labora.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"kernel@...labora.com" <kernel@...labora.com>, "robh@...nel.org"
	<robh@...nel.org>, "kw@...ux.com" <kw@...ux.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "matthias.bgg@...il.com"
	<matthias.bgg@...il.com>, "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>, Ryder Lee
	<Ryder.Lee@...iatek.com>, "fshao@...omium.org" <fshao@...omium.org>
Subject: Re: [PATCH v3 2/2] PCI: mediatek-gen3: Add support for restricting
 link width

Hi Angelo,

Thanks for your patch.

On Wed, 2024-09-18 at 10:13 +0200, 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).
> 
> Signed-off-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@...labora.com>
> ---
>  drivers/pci/controller/pcie-mediatek-gen3.c | 20
> ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c
> b/drivers/pci/controller/pcie-mediatek-gen3.c
> index 8d4b045633da..8dd2e5135b01 100644
> --- a/drivers/pci/controller/pcie-mediatek-gen3.c
> +++ b/drivers/pci/controller/pcie-mediatek-gen3.c
> @@ -32,6 +32,7 @@
>  #define PCIE_BASE_CFG_SPEED		GENMASK(15, 8)
>  
>  #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(pcie->num_lanes >> 1,
> 0));

It should be GENMASK(fls(pcie->num_lanes) - 2, 0).

Thanks.

> +	};
>  	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;
>  }
>