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From: Rob Herring <robh@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Jason Cooper" <jason@lakedaemon.net>,
	"Andrew Lunn" <andrew@lunn.ch>,
	"Gregory Clement" <gregory.clement@bootlin.com>,
	"Sebastian Hesselbarth" <sebastian.hesselbarth@gmail.com>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Andrew Murray" <amurray@thegoodpenguin.co.uk>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Remi Pommarel" <repk@triplefau.lt>,
	"Marek Behún" <marek.behun@nic.cz>,
	"Tomasz Maciej Nowak" <tmn505@gmail.com>,
	Xogium <contact@xogium.me>,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org
Subject: Re: [PATCH v4 05/12] PCI: aardvark: Issue PERST via GPIO
Date: Thu, 7 May 2020 16:20:02 -0500	[thread overview]
Message-ID: <20200507212002.GA32182@bogus> (raw)
In-Reply-To: <20200430082245.xblvb7xeamm4e336@pali>

On Thu, Apr 30, 2020 at 10:22:45AM +0200, Pali Rohár wrote:
> On Thursday 30 April 2020 10:06:18 Pali Rohár wrote:
> > +static void advk_pcie_issue_perst(struct advk_pcie *pcie)
> > +{
> > +	u32 reg;
> > +
> > +	if (!pcie->reset_gpio)
> > +		return;
> > +
> > +	/* PERST does not work for some cards when link training is enabled */
> > +	reg = advk_readl(pcie, PCIE_CORE_CTRL0_REG);
> > +	reg &= ~LINK_TRAINING_EN;
> > +	advk_writel(pcie, reg, PCIE_CORE_CTRL0_REG);
> > +
> > +	/* 10ms delay is needed for some cards */
> > +	dev_info(&pcie->pdev->dev, "issuing PERST via reset GPIO for 10ms\n");
> > +	gpiod_set_value_cansleep(pcie->reset_gpio, 1);
> > +	usleep_range(10000, 11000);
> > +	gpiod_set_value_cansleep(pcie->reset_gpio, 0);
> > +}
> 
> Just note about delay between changing GPIO reset:
> 
> In V2 there as only 1ms, but be figured out that it is not enough for
> WLE900VX cards when they were already initialized in u-boot.
> 
> I tried to find in PCI specs if there is a defined timeout for this
> operation. I found following 3 delay definitions which could be related:
> 
> TPVPERL - PERST# must remain active at least this long after power becomes valid
> TPERST - When asserted, PERST# must remain asserted at least this long
> TPERSTCLK - PERST# must remain active at least this long after any supplied reference clock is stable
> 
> In another spec they have defined also minimal values:
> 
> TPVPERL - Power stable to PERST# inactive - Min 100 ms
> TPERST - PERST# active time - Min 100 us
> TPERSTCLK - REFCLK stable before PERST# inactive - Min 100 us
> 
> After experimenting with those Compex WLE900VX cards, I know that 100us
> delay is not enough. And I'm not sure if TPVPERL is really relevant for
> this case. I understood that TPVPERL is needed when initializing power
> again. And because delaying boot by another 100ms is does not have to be
> acceptable if there is not strict reason for it, I rather decided to
> stay with just 10ms delay.
> 
> If you know what is the correct timeout between changing GPIO reset,
> please let me know and in future I can fix/reimplement it.

I don't know, but seems like something each driver author shouldn't be 
making up.

Rob


  reply	other threads:[~2020-05-07 21:20 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-30  8:06 [PATCH v4 00/12] PCI: aardvark: Fix support for Turris MOX and Compex wifi cards Pali Rohár
2020-04-30  8:06 ` [PATCH v4 01/12] PCI: aardvark: Train link immediately after enabling training Pali Rohár
2020-05-04 15:50   ` Bjorn Helgaas
2020-05-07 21:05   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 02/12] PCI: aardvark: Don't blindly enable ASPM L0s and don't write to read-only register Pali Rohár
2020-05-07 21:07   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 03/12] PCI: of: Zero max-link-speed value is invalid Pali Rohár
2020-05-07 21:07   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 04/12] PCI: aardvark: Improve link training Pali Rohár
2020-05-07 21:10   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 05/12] PCI: aardvark: Issue PERST via GPIO Pali Rohár
2020-04-30  8:22   ` Pali Rohár
2020-05-07 21:20     ` Rob Herring [this message]
2020-04-30  8:06 ` [PATCH v4 06/12] PCI: aardvark: Add FIXME comment for PCIE_CORE_CMD_STATUS_REG access Pali Rohár
2020-05-07 21:20   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 07/12] PCI: aardvark: Add PHY support Pali Rohár
2020-05-07 21:23   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 08/12] PCI: aardvark: Replace custom macros by standard linux/pci_regs.h macros Pali Rohár
2020-05-04 15:52   ` Bjorn Helgaas
2020-05-07 21:24   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 09/12] dt-bindings: PCI: aardvark: Describe new properties Pali Rohár
2020-05-07 21:25   ` Rob Herring
2020-04-30  8:06 ` [PATCH v4 10/12] arm64: dts: marvell: armada-37xx: Set pcie_reset_pin to gpio function Pali Rohár
2020-04-30  8:06 ` [PATCH v4 11/12] arm64: dts: marvell: armada-37xx: Move PCIe comphy handle property Pali Rohár
2020-04-30  8:06 ` [PATCH v4 12/12] arm64: dts: marvell: armada-37xx: Move PCIe max-link-speed property Pali Rohár
2020-05-04 15:50   ` Bjorn Helgaas
2020-05-08 13:11 ` [PATCH v4 00/12] PCI: aardvark: Fix support for Turris MOX and Compex wifi cards Tomasz Maciej Nowak
2020-05-13 11:16 ` Pali Rohár
2020-05-13 11:33   ` Lorenzo Pieralisi
2020-05-13 11:59     ` Pali Rohár
2020-05-13 11:56 ` Thomas Petazzoni
2020-05-17 15:57   ` Gregory CLEMENT
2020-05-18 10:30     ` Pali Rohár
2020-05-18 13:46       ` Lorenzo Pieralisi
2020-05-18 13:50         ` Marek Behun

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