linux-kernel - Re: [PATCH v5] PCI: j721e: Delay T_PVPERL+TPERST

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Message-ID: <c671e9f3-c932-4461-bcfc-3b320bf43483@ti.com>
Date:   Fri, 1 Dec 2023 16:22:44 +0530
From:   Siddharth Vadapalli <s-vadapalli@...com>
To:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     Krzysztof Wilczy_ski <kw@...ux.com>, Rob Herring <robh@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Tom Joseph <tjoseph@...ence.com>, <linux-omap@...r.kernel.org>,
        <linux-pci@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <s-vadapalli@...com>
Subject: Re: [PATCH v5] PCI: j721e: Delay T_PVPERL+TPERST_CLK before PERST#
 inactive

Hello Lorenzo, Bjorn,

On 17/08/23 15:06, Achal Verma wrote:
> As per the PCIe Card Electromechanical specification REV. 5.0, PERST#
> signal should be de-asserted after minimum 100ms from the time power-rails
> achieve specified operating limits and 100us after reference clock gets
> stable.
> 
> From PCIe Card Electromechanical specification REV. 5.0 section 2.9.2:
> TPVPERL: Power stable to PERST# inactive - 100ms
> TPERST_CLK: REFCLK stable before PERST# inactive - 100us
> 
> Fixes: f3e25911a430 ("PCI: j721e: Add TI J721E PCIe driver")
> Signed-off-by: Achal Verma <a-verma1@...com>
> ---
>  drivers/pci/controller/cadence/pci-j721e.c | 30 +++++++++++-----------
>  drivers/pci/pci.h                          |  3 +++
>  2 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index e70213c9060a..b09924b010ab 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -34,6 +34,8 @@
>  #define J721E_PCIE_USER_LINKSTATUS	0x14
>  #define LINK_STATUS			GENMASK(1, 0)
>  
> +#define PERST_INACTIVE_US (PCIE_TPVPERL_MS*USEC_PER_MSEC + PCIE_TPERST_CLK_US)

This implementation appears incorrect to me since T_PVPERL already accounts for
T_PERST-CLK according to Figure 2-3 of PCI Express Card Electromechanical
Specification Revision 5.1:
https://members.pcisig.com/wg/PCI-SIG/document/19922

Could you please share your opinion since I wish to post a v6 for this patch,
rebasing it to the latest tree which has the commit:
164f66be0c25 PCI: Add T_PVPERL macro
The macro can be used in the current patch, instead of the PERST_INACTIVE_US macro.

> +
>  enum link_status {
>  	NO_RECEIVERS_DETECTED,
>  	LINK_TRAINING_IN_PROGRESS,
> @@ -359,7 +361,7 @@ static int j721e_pcie_probe(struct platform_device *pdev)
>  	struct j721e_pcie *pcie;
>  	struct cdns_pcie_rc *rc = NULL;
>  	struct cdns_pcie_ep *ep = NULL;
> -	struct gpio_desc *gpiod;
> +	struct gpio_desc *perst_gpiod;
>  	void __iomem *base;
>  	struct clk *clk;
>  	u32 num_lanes;
> @@ -468,11 +470,10 @@ static int j721e_pcie_probe(struct platform_device *pdev)
>  
>  	switch (mode) {
>  	case PCI_MODE_RC:
> -		gpiod = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
> -		if (IS_ERR(gpiod)) {
> -			ret = PTR_ERR(gpiod);
> -			if (ret != -EPROBE_DEFER)
> -				dev_err(dev, "Failed to get reset GPIO\n");
> +		perst_gpiod = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
> +		if (IS_ERR(perst_gpiod)) {
> +			ret = PTR_ERR(perst_gpiod);
> +			dev_err(dev, "Failed to get reset GPIO\n");
>  			goto err_get_sync;
>  		}
>  
> @@ -498,16 +499,15 @@ static int j721e_pcie_probe(struct platform_device *pdev)
>  
>  		/*
>  		 * "Power Sequencing and Reset Signal Timings" table in
> -		 * PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION, REV. 3.0
> -		 * indicates PERST# should be deasserted after minimum of 100us
> -		 * once REFCLK is stable. The REFCLK to the connector in RC
> -		 * mode is selected while enabling the PHY. So deassert PERST#
> -		 * after 100 us.
> +		 * PCI EXPRESS CARD ELECTROMECHANICAL SPECIFICATION, REV. 5.0
> +		 * indicates PERST# should be deasserted after minimum of 100ms
> +		 * after power rails achieve specified operating limits and
> +		 * 100us after reference clock gets stable.
> +		 * PERST_INACTIVE_US accounts for both delays.
>  		 */
> -		if (gpiod) {
> -			usleep_range(100, 200);
> -			gpiod_set_value_cansleep(gpiod, 1);
> -		}
> +
> +		fsleep(PERST_INACTIVE_US);
> +		gpiod_set_value_cansleep(perst_gpiod, 1);
>  
>  		ret = cdns_pcie_host_setup(rc);
>  		if (ret < 0) {
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index a4c397434057..80d520be34e6 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -13,6 +13,9 @@
>  
>  #define PCIE_LINK_RETRAIN_TIMEOUT_MS	1000
>  
> +#define PCIE_TPVPERL_MS		100	/* see PCIe CEM r5.0, sec 2.9.2 */
> +#define PCIE_TPERST_CLK_US	100
> +
>  extern const unsigned char pcie_link_speed[];
>  extern bool pci_early_dump;
>  

-- 
Regards,
Siddharth.