linux-kernel - Re: [PATCH v3] PCI: cadence: Retrain Link to work around Gen2 training defect.

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Date:   Mon, 19 Oct 2020 10:58:39 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Nadeem Athani <nadeem@...ence.com>, <lorenzo.pieralisi@....com>,
        <robh@...nel.org>, <bhelgaas@...gle.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <tjoseph@...ence.com>
CC:     <sjakhade@...ence.com>, <mparab@...ence.com>
Subject: Re: [PATCH v3] PCI: cadence: Retrain Link to work around Gen2
 training defect.

Hi Nadeem,

On 30/09/20 11:51 pm, Nadeem Athani wrote:
> Cadence controller will not initiate autonomous speed change if strapped
> as Gen2. The Retrain Link bit is set as quirk to enable this speed change.
> 
> Signed-off-by: Nadeem Athani <nadeem@...ence.com>
> ---
> Changes in v3:
> - To set retrain link bit,checking device capability & link status.
> - 32bit read in place of 8bit.
> - Minor correction in patch comment.
> - Change in variable & macro name.
> Changes in v2:
> - 16bit read in place of 8bit.
>  drivers/pci/controller/cadence/pcie-cadence-host.c | 31 ++++++++++++++++++++++
>  drivers/pci/controller/cadence/pcie-cadence.h      |  9 ++++++-
>  2 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
> index 4550e0d469ca..2b2ae4e18032 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> @@ -77,6 +77,36 @@ static struct pci_ops cdns_pcie_host_ops = {
>  	.write		= pci_generic_config_write,
>  };
>  
> +static void cdns_pcie_retrain(struct cdns_pcie *pcie)
> +{
> +	u32 lnk_cap_sls, pcie_cap_off = CDNS_PCIE_RP_CAP_OFFSET;
> +	u16 lnk_stat, lnk_ctl;
> +
> +	if (!cdns_pcie_link_up(pcie))
> +		return;
> +

Is there a IP version that can be used to check if that quirk is applicable?
> +	/*
> +	 * Set retrain bit if current speed is 2.5 GB/s,
> +	 * but the PCIe root port support is > 2.5 GB/s.
> +	 */
> +
> +	lnk_cap_sls = cdns_pcie_readl(pcie, (CDNS_PCIE_RP_BASE + pcie_cap_off +
> +				      PCI_EXP_LNKCAP));
> +	if ((lnk_cap_sls & PCI_EXP_LNKCAP_SLS) <= PCI_EXP_LNKCAP_SLS_2_5GB)
> +		return;
> +
> +	lnk_stat = cdns_pcie_rp_readw(pcie, pcie_cap_off + PCI_EXP_LNKSTA);
> +	if ((lnk_stat & PCI_EXP_LNKSTA_CLS) == PCI_EXP_LNKSTA_CLS_2_5GB) {
> +		lnk_ctl = cdns_pcie_rp_readw(pcie,
> +					     pcie_cap_off + PCI_EXP_LNKCTL);
> +		lnk_ctl |= PCI_EXP_LNKCTL_RL;
> +		cdns_pcie_rp_writew(pcie, pcie_cap_off + PCI_EXP_LNKCTL,
> +				    lnk_ctl);
> +
> +		if (!cdns_pcie_link_up(pcie))

Should this rather be a cdns_pcie_host_wait_for_link()?

Thanks
Kishon

> +			return;
> +	}
> +}
>  
>  static int cdns_pcie_host_init_root_port(struct cdns_pcie_rc *rc)
>  {
> @@ -115,6 +145,7 @@ static int cdns_pcie_host_init_root_port(struct cdns_pcie_rc *rc)
>  	cdns_pcie_rp_writeb(pcie, PCI_CLASS_PROG, 0);
>  	cdns_pcie_rp_writew(pcie, PCI_CLASS_DEVICE, PCI_CLASS_BRIDGE_PCI);
>  
> +	cdns_pcie_retrain(pcie);
>  	return 0;
>  }
>  
> diff --git a/drivers/pci/controller/cadence/pcie-cadence.h b/drivers/pci/controller/cadence/pcie-cadence.h
> index feed1e3038f4..5f1cf032ae15 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence.h
> +++ b/drivers/pci/controller/cadence/pcie-cadence.h
> @@ -119,7 +119,7 @@
>   * Root Port Registers (PCI configuration space for the root port function)
>   */
>  #define CDNS_PCIE_RP_BASE	0x00200000
> -
> +#define CDNS_PCIE_RP_CAP_OFFSET 0xc0
>  
>  /*
>   * Address Translation Registers
> @@ -413,6 +413,13 @@ static inline void cdns_pcie_rp_writew(struct cdns_pcie *pcie,
>  	cdns_pcie_write_sz(addr, 0x2, value);
>  }
>  
> +static inline u16 cdns_pcie_rp_readw(struct cdns_pcie *pcie, u32 reg)
> +{
> +	void __iomem *addr = pcie->reg_base + CDNS_PCIE_RP_BASE + reg;
> +
> +	return cdns_pcie_read_sz(addr, 0x2);
> +}
> +
>  /* Endpoint Function register access */
>  static inline void cdns_pcie_ep_fn_writeb(struct cdns_pcie *pcie, u8 fn,
>  					  u32 reg, u8 value)
>