linux-kernel - Re: [PATCH 5/8] PCI: aardvark: Set final controller speed based on negotiated link speed

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Date:   Sun, 19 Apr 2020 05:17:11 +0200
From:   Marek Behun <marek.behun@....cz>
To:     Pali Rohár <pali@...nel.org>
Cc:     Jason Cooper <jason@...edaemon.net>, Andrew Lunn <andrew@...n.ch>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Murray <amurray@...goodpenguin.co.uk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Remi Pommarel <repk@...plefau.lt>,
        Tomasz Maciej Nowak <tmn505@...il.com>,
        Xogium <contact@...ium.me>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 5/8] PCI: aardvark: Set final controller speed based on
 negotiated link speed

On Wed, 15 Apr 2020 18:03:45 +0200
Pali Rohár <pali@...nel.org> wrote:

> Some Compex WLE900VX gen1 cards are unstable or even not detected when
> aardvark PCI controller speed is set to gen2. Moreover when ASPM code tries
> to retrain link second time then these cards stop responding and link goes
> down. If aardvark PCI controller is set to gen1 then these cards work fine
> without any problem.
> 
> Unconditionally forcing aardvark controller to gen1 speed (either via DT
> property max-link-speed or hardcoded value in driver itself) is not a
> solution as it would have performance impact for fast gen2 sata cards.
> 
> To overcome this problem, try all 3 possible speeds (gen3, gen2, gen1)
> supported by aardvark PCI controller with respect to max-link-speed setting
> and after successful link training choose final controller speed based on
> Negotiated Link Speed from Link Status register, which should match card
> speed.
> 
> I tested this change with Compex cards WLE200NX (pcie 1.0, gen1, ath9k),
> WLE900VX (pcie 1.1, gen1, ath10k) and WLE1216V5-20 (pcie 2.0, gen2, ath10k)
> on Turris MOX. Tomasz Maciej Nowak tested JJPlus JWX6051 (ath9k), Intel
> 622ANHMW, MT76 U7612E-H1 and Compex WLE1216V2-20 cards on Espressobin.
> 
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  drivers/pci/controller/pci-aardvark.c | 35 +++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c
> index 02c69fc9aadf..a83bbc86e428 100644
> --- a/drivers/pci/controller/pci-aardvark.c
> +++ b/drivers/pci/controller/pci-aardvark.c
> @@ -40,6 +40,7 @@
>  #define PCIE_CORE_LINK_CTRL_STAT_REG				0xd0
>  #define     PCIE_CORE_LINK_L0S_ENTRY				BIT(0)
>  #define     PCIE_CORE_LINK_TRAINING				BIT(5)
> +#define     PCIE_CORE_LINK_SPEED_SHIFT				16
>  #define     PCIE_CORE_LINK_WIDTH_SHIFT				20
>  #define PCIE_CORE_ERR_CAPCTL_REG				0x118
>  #define     PCIE_CORE_ERR_CAPCTL_ECRC_CHK_TX			BIT(5)
> @@ -276,7 +277,7 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>  {
>  	struct device *dev = &pcie->pdev->dev;
>  	struct device_node *node = dev->of_node;
> -	int max_link_speed;
> +	int max_link_speed, neg_link_speed;
>  	u32 reg;
>  
>  	/* Set to Direct mode */
> @@ -378,7 +379,37 @@ static void advk_pcie_setup_hw(struct advk_pcie *pcie)
>  	reg |= PCIE_CORE_LINK_TRAINING;
>  	advk_writel(pcie, reg, PCIE_CORE_LINK_CTRL_STAT_REG);
>  
> -	advk_pcie_wait_for_link(pcie);
> +	do {
> +		if (advk_pcie_wait_for_link(pcie) < 0) {
> +			max_link_speed--;
> +		} else {
> +			reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
> +
> +			neg_link_speed =
> +				(reg >> PCIE_CORE_LINK_SPEED_SHIFT) & 0xf;
> +			dev_info(dev, "negotiated link speed %d\n",
> +				neg_link_speed);
> +
> +			if (neg_link_speed == max_link_speed)
> +				break;
> +
> +			if (neg_link_speed > 0 && neg_link_speed <= 3)
> +				max_link_speed = neg_link_speed;
> +			else
> +				max_link_speed--;
> +		}
> +
> +		if (max_link_speed == 0)
> +			break;
> +
> +		/* Set new decreased max link speed */
> +		advk_pcie_setup_link_speed(pcie, max_link_speed);
> +
> +		/* And start link training again */
> +		reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
> +		reg |= PCIE_CORE_LINK_TRAINING;
> +		advk_writel(pcie, reg, PCIE_CORE_LINK_CTRL_STAT_REG);
> +	} while (1);
>  

This do {} while(1) should be a for cycle iterating the max_link_speed
variable, and probably in a separate function
advk_pcie_negotiate_link_speed.

A3700, which is the only SOC to use this driver, does not support PCIe
gen 3, so this shouldn't be tried, at least if
.compatible == "marvell,armada-3700-pcie".

Marek