linux-kernel - [PATCH 4.14 034/106] PCI: aardvark: Wait for endpoint to be ready before training link

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Message-Id: <20211206145556.541978437@linuxfoundation.org>
Date:   Mon,  6 Dec 2021 15:55:42 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Remi Pommarel <repk@...plefau.lt>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marek Behún <kabel@...nel.org>
Subject: [PATCH 4.14 034/106] PCI: aardvark: Wait for endpoint to be ready before training link

From: Remi Pommarel <repk@...plefau.lt>

commit f4c7d053d7f77cd5c1a1ba7c7ce085ddba13d1d7 upstream.

When configuring pcie reset pin from gpio (e.g. initially set by
u-boot) to pcie function this pin goes low for a brief moment
asserting the PERST# signal. Thus connected device enters fundamental
reset process and link configuration can only begin after a minimal
100ms delay (see [1]).

Because the pin configuration comes from the "default" pinctrl it is
implicitly configured before the probe callback is called:

driver_probe_device()
  really_probe()
    ...
    pinctrl_bind_pins() /* Here pin goes from gpio to PCIE reset
                           function and PERST# is asserted */
    ...
    drv->probe()

[1] "PCI Express Base Specification", REV. 4.0
    PCI Express, February 19 2014, 6.6.1 Conventional Reset

Signed-off-by: Remi Pommarel <repk@...plefau.lt>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Signed-off-by: Marek Behún <kabel@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/pci/host/pci-aardvark.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/drivers/pci/host/pci-aardvark.c
+++ b/drivers/pci/host/pci-aardvark.c
@@ -362,6 +362,14 @@ static void advk_pcie_setup_hw(struct ad
 	reg |= PIO_CTRL_ADDR_WIN_DISABLE;
 	advk_writel(pcie, reg, PIO_CTRL);
 
+	/*
+	 * PERST# signal could have been asserted by pinctrl subsystem before
+	 * probe() callback has been called, making the endpoint going into
+	 * fundamental reset. As required by PCI Express spec a delay for at
+	 * least 100ms after such a reset before link training is needed.
+	 */
+	msleep(PCI_PM_D3COLD_WAIT);
+
 	/* Start link training */
 	reg = advk_readl(pcie, PCIE_CORE_LINK_CTRL_STAT_REG);
 	reg |= PCIE_CORE_LINK_TRAINING;