linux-kernel - Re: [PATCH 2/2] PCI: cadence: Set LTSSM Detect.Quiet state delay.

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Date:   Mon, 15 Mar 2021 18:41:44 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Nadeem Athani <nadeem@...ence.com>, <tjoseph@...ence.com>,
        <bhelgaas@...gle.com>, <robh+dt@...nel.org>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lorenzo.pieralisi@....com>,
        <robh@...nel.org>
CC:     <mparab@...ence.com>, <sjakhade@...ence.com>,
        <pthombar@...ence.com>
Subject: Re: [PATCH 2/2] PCI: cadence: Set LTSSM Detect.Quiet state delay.

Hi Nadeem,

On 09/03/21 1:01 pm, Nadeem Athani wrote:
> The parameter detect_quiet_min_delay can be used to program the minimum
> time that LTSSM waits on entering Detect.Quiet state.
> 00 : 0us minimum wait time in Detect.Quiet state.
> 01 : 100us minimum wait time in Detect.Quiet state.
> 10 : 1000us minimum wait time in Detect.Quiet state.
> 11 : 2000us minimum wait time in Detect.Quiet state.
> 
> As per PCIe specification, all Receivers must meet the Z-RX-DC
> specification for 2.5 GT/s within 1000us of entering Detect.Quiet LTSSM
> substate. The LTSSM must stay in this substate until the ZRXDC
> specification for 2.5 GT/s is met.
> 
> Signed-off-by: Nadeem Athani <nadeem@...ence.com>
> ---
>  drivers/pci/controller/cadence/pcie-cadence-host.c | 22 ++++++++++++++++++++++
>  drivers/pci/controller/cadence/pcie-cadence.h      | 10 ++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
> index 73dcf8cf98fb..056161b3fe65 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> @@ -461,6 +461,20 @@ static int cdns_pcie_host_init(struct device *dev,
>  	return cdns_pcie_host_init_address_translation(rc);
>  }
>  
> +static void cdns_pcie_detect_quiet_min_delay_set(struct cdns_pcie_rc *rc)
> +{
> +	struct cdns_pcie *pcie = &rc->pcie;
> +	u32 delay = rc->detect_quiet_min_delay;
> +	u32 ltssm_control_cap;
> +
> +	ltssm_control_cap = cdns_pcie_readl(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP);
> +	ltssm_control_cap = ((ltssm_control_cap &
> +			     ~CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK) |
> +			    CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay));
> +
> +	cdns_pcie_writel(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP, ltssm_control_cap);
> +}
> +

The issue is not specific to only host mode.

Thanks
Kishon
>  int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
>  {
>  	struct device *dev = rc->pcie.dev;
> @@ -485,6 +499,10 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
>  	rc->device_id = 0xffff;
>  	of_property_read_u32(np, "device-id", &rc->device_id);
>  
> +	rc->detect_quiet_min_delay = 0;
> +	of_property_read_u32(np, "detect-quiet-min-delay",
> +			     &rc->detect_quiet_min_delay);
> +
>  	pcie->reg_base = devm_platform_ioremap_resource_byname(pdev, "reg");
>  	if (IS_ERR(pcie->reg_base)) {
>  		dev_err(dev, "missing \"reg\"\n");
> @@ -497,6 +515,10 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
>  		return PTR_ERR(rc->cfg_base);
>  	rc->cfg_res = res;
>  
> +	/* Default Detect.Quiet state delay is 0 */
> +	if (rc->detect_quiet_min_delay)
> +		cdns_pcie_detect_quiet_min_delay_set(rc);
> +
>  	ret = cdns_pcie_start_link(pcie);
>  	if (ret) {
>  		dev_err(dev, "Failed to start link\n");
> diff --git a/drivers/pci/controller/cadence/pcie-cadence.h b/drivers/pci/controller/cadence/pcie-cadence.h
> index 254d2570f8c9..f2d3cca2c707 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence.h
> +++ b/drivers/pci/controller/cadence/pcie-cadence.h
> @@ -189,6 +189,14 @@
>  /* AXI link down register */
>  #define CDNS_PCIE_AT_LINKDOWN (CDNS_PCIE_AT_BASE + 0x0824)
>  
> +/* LTSSM Capabilities register */
> +#define CDNS_PCIE_LTSSM_CONTROL_CAP		 (CDNS_PCIE_LM_BASE + 0x0054)
> +#define  CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK	 GENMASK(2, 1)
> +#define  CDNS_PCIE_DETECT_QUIET_MIN_DELAY_SHIFT 1
> +#define  CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay) \
> +	  (((delay) << CDNS_PCIE_DETECT_QUIET_MIN_DELAY_SHIFT) & \
> +	  CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK)
> +
>  enum cdns_pcie_rp_bar {
>  	RP_BAR_UNDEFINED = -1,
>  	RP_BAR0,
> @@ -289,6 +297,7 @@ struct cdns_pcie {
>   *            single function at a time
>   * @vendor_id: PCI vendor ID
>   * @device_id: PCI device ID
> + * @detect_quiet_min_delay: LTSSM Detect Quite state min. delay
>   * @avail_ib_bar: Satus of RP_BAR0, RP_BAR1 and	RP_NO_BAR if it's free or
>   *                available
>   * @quirk_retrain_flag: Retrain link as quirk for PCIe Gen2
> @@ -299,6 +308,7 @@ struct cdns_pcie_rc {
>  	void __iomem		*cfg_base;
>  	u32			vendor_id;
>  	u32			device_id;
> +	u32			detect_quiet_min_delay;
>  	bool			avail_ib_bar[CDNS_PCIE_RP_MAX_IB];
>  	bool                    quirk_retrain_flag;
>  };
>