linux-kernel - [PATCH] PCI: apple: Reset the port for 100ms on probe

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Message-Id: <20211117160053.232158-1-maz@kernel.org>
Date:   Wed, 17 Nov 2021 16:00:53 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pci@...r.kernel.org
Cc:     kernel-team@...roid.com, Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>
Subject: [PATCH] PCI: apple: Reset the port for 100ms on probe

While the Apple PCIe driver works correctly when directly booted
from the firmware, it fails to initialise when the kernel is booted
from a bootloader using PCIe such as u-boot.

That's beacuse we're missing a proper reset of the port (we only
clear the reset, but never assert it).

Bring the port back to life by wiggling the #PERST pin for 100ms
(as per the spec).

Fixes: 1e33888fbe44 ("PCI: apple: Add initial hardware bring-up")
Signed-off-by: Marc Zyngier <maz@...nel.org>
Cc: Alyssa Rosenzweig <alyssa@...enzweig.io>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
---
 drivers/pci/controller/pcie-apple.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
index 1bf4d75b61be..bbea5f6e0a68 100644
--- a/drivers/pci/controller/pcie-apple.c
+++ b/drivers/pci/controller/pcie-apple.c
@@ -543,6 +543,9 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie,
 	if (ret < 0)
 		return ret;
 
+	/* Hold #PERST for 100ms as per the spec */
+	gpiod_set_value(reset, 0);
+	msleep(100);
 	rmw_set(PORT_PERST_OFF, port->base + PORT_PERST);
 	gpiod_set_value(reset, 1);
 
-- 
2.30.2