linux-kernel - Re: [PATCH v5 11/11] PCI: qcom: Add Force GEN1 support

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Date:   Tue, 2 Jun 2020 11:32:55 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Sham Muthayyan <smuthayy@...eaurora.org>,
        Rob Herring <robh@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 11/11] PCI: qcom: Add Force GEN1 support

On Tue, Jun 02, 2020 at 01:53:52PM +0200, Ansuel Smith wrote:
> From: Sham Muthayyan <smuthayy@...eaurora.org>
> 
> Add Force GEN1 support needed in some ipq8064 board that needs to limit
> some PCIe line to gen1 for some hardware limitation. This is set by the
> max-link-speed binding and needed by some soc based on ipq8064. (for
> example Netgear R7800 router)
> 
> Signed-off-by: Sham Muthayyan <smuthayy@...eaurora.org>
> Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> Reviewed-by: Rob Herring <robh@...nel.org>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 259b627bf890..0ce15d53c46e 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -27,6 +27,7 @@
>  #include <linux/slab.h>
>  #include <linux/types.h>
>  
> +#include "../../pci.h"
>  #include "pcie-designware.h"
>  
>  #define PCIE20_PARF_SYS_CTRL			0x00
> @@ -99,6 +100,8 @@
>  #define PCIE20_v3_PARF_SLV_ADDR_SPACE_SIZE	0x358
>  #define SLV_ADDR_SPACE_SZ			0x10000000
>  
> +#define PCIE20_LNK_CONTROL2_LINK_STATUS2	0xa0
> +
>  #define DEVICE_TYPE_RC				0x4
>  
>  #define QCOM_PCIE_2_1_0_MAX_SUPPLY	3
> @@ -195,6 +198,7 @@ struct qcom_pcie {
>  	struct phy *phy;
>  	struct gpio_desc *reset;
>  	const struct qcom_pcie_ops *ops;
> +	int gen;
>  };
>  
>  #define to_qcom_pcie(x)		dev_get_drvdata((x)->dev)
> @@ -395,6 +399,11 @@ static int qcom_pcie_init_2_1_0(struct qcom_pcie *pcie)
>  	/* wait for clock acquisition */
>  	usleep_range(1000, 1500);
>  
> +	if (pcie->gen == 1) {
> +		val = readl(pci->dbi_base + PCIE20_LNK_CONTROL2_LINK_STATUS2);
> +		val |= 1;

Is this the same bit that's visible in config space as
PCI_EXP_LNKSTA_CLS_2_5GB?  Why not use that #define?

There are a bunch of other #defines in this file that look like
redefinitions of standard things:

  #define PCIE20_COMMAND_STATUS                   0x04
    Looks like PCI_COMMAND

  #define CMD_BME_VAL                             0x4
    Looks like PCI_COMMAND_MASTER

  #define PCIE20_DEVICE_CONTROL2_STATUS2          0x98
    Looks like (PCIE20_CAP + PCI_EXP_DEVCTL2)

  #define PCIE_CAP_CPL_TIMEOUT_DISABLE            0x10
    Looks like PCI_EXP_DEVCTL2_COMP_TMOUT_DIS

  #define PCIE20_CAP                              0x70
    This one is obviously device-specific

  #define PCIE20_CAP_LINK_CAPABILITIES            (PCIE20_CAP + 0xC)
    Looks like (PCIE20_CAP + PCI_EXP_LNKCAP)

  #define PCIE20_CAP_ACTIVE_STATE_LINK_PM_SUPPORT (BIT(10) | BIT(11))
    Looks like PCI_EXP_LNKCAP_ASPMS

  #define PCIE20_CAP_LINK_1                       (PCIE20_CAP + 0x14)
  #define PCIE_CAP_LINK1_VAL                      0x2FD7F
    This looks like PCIE20_CAP_LINK_1 should be (PCIE20_CAP +
    PCI_EXP_SLTCAP), but "CAP_LINK_1" doesn't sound like the Slot
    Capabilities register, and I don't know what PCIE_CAP_LINK1_VAL
    means.

> +		writel(val, pci->dbi_base + PCIE20_LNK_CONTROL2_LINK_STATUS2);
> +	}
>  
>  	/* Set the Max TLP size to 2K, instead of using default of 4K */
>  	writel(CFG_REMOTE_RD_REQ_BRIDGE_SIZE_2K,
> @@ -1397,6 +1406,10 @@ static int qcom_pcie_probe(struct platform_device *pdev)
>  		goto err_pm_runtime_put;
>  	}
>  
> +	pcie->gen = of_pci_get_max_link_speed(pdev->dev.of_node);
> +	if (pcie->gen < 0)
> +		pcie->gen = 2;
> +
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "parf");
>  	pcie->parf = devm_ioremap_resource(dev, res);
>  	if (IS_ERR(pcie->parf)) {
> -- 
> 2.25.1
>