linux-kernel - Re: [PATCH v3] PCI: j721e: Delay 100ms T_PVPERL from power stable to PERST# inactive

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Date:   Fri, 14 Jul 2023 12:16:07 +0530
From:   "Verma, Achal" <a-verma1@...com>
To:     Vignesh Raghavendra <vigneshr@...com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczy_ski <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>
CC:     <linux-omap@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Achal Verma <a-verma1@...com>
Subject: Re: [PATCH v3] PCI: j721e: Delay 100ms T_PVPERL from power stable to
 PERST# inactive



On 7/7/2023 3:21 PM, 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
> become stable. So, to ensure 100ms delay to give sufficient time for
> power-rails and refclk to become stable, change delay from 100us to 100ms.
> 
>  From PCIe Card Electromechanical specification REV. 5.0 section 2.9.2:
> TPVPERL: Power stable to PERST# inactive - 100ms
> 
> Fixes: f3e25911a430 ("PCI: j721e: Add TI J721E PCIe driver")
> Signed-off-by: Achal Verma <a-verma1@...com>
Hello Bjorn,

Could you please bless this with "Reviewed-by" tag.

Thanks,
Achal Verma
> ---
> 
> Changes from v2:
> * Fix commit message.
> 
> Change from v1:
> * Add macro for delay value.
> 
>   drivers/pci/controller/cadence/pci-j721e.c | 11 +++++------
>   drivers/pci/pci.h                          |  2 ++
>   2 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index e70213c9060a..32b6a7dc3cff 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -498,14 +498,13 @@ 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
> +		 * within this period reference clock should also become stable.
>   		 */
>   		if (gpiod) {
> -			usleep_range(100, 200);
> +			msleep(PCIE_TPVPERL_DELAY_MS);
>   			gpiod_set_value_cansleep(gpiod, 1);
>   		}
>   
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index a4c397434057..6ab2367e5867 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -13,6 +13,8 @@
>   
>   #define PCIE_LINK_RETRAIN_TIMEOUT_MS	1000
>   
> +#define PCIE_TPVPERL_DELAY_MS	100	/* see PCIe CEM r5.0, sec 2.9.2 */
> +
>   extern const unsigned char pcie_link_speed[];
>   extern bool pci_early_dump;
>