From: Luca Ceresoli <luca@lucaceresoli.net>
To: linux-pci@vger.kernel.org
Cc: Luca Ceresoli <luca@lucaceresoli.net>,
linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Kishon Vijay Abraham I <kishon@ti.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Rob Herring <robh@kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>
Subject: [PATCH] PCI: dwc: pci-dra7xx: fix reset behaviour
Date: Mon, 17 May 2021 17:35:57 +0200 [thread overview]
Message-ID: <20210517153557.429623-1-luca@lucaceresoli.net> (raw)
The PCIe PERSTn reset pin is active low and should be asserted, then
deasserted.
The current implementation only drives the pin once in "HIGH" position,
thus presumably it was intended to deassert the pin. This has two problems:
1) it assumes the pin was asserted by other means before loading the
driver
2) it has the wrong polarity, since "HIGH" means "active", and the pin is
presumably configured as active low coherently with the PCIe
convention, thus it is driven physically to 0, keeping the device
under reset unless the pin is configured as active high.
Fix both problems by:
1) keeping devm_gpiod_get_optional(dev, NULL, GPIOD_OUT_HIGH) as is, but
assuming the pin is correctly configured as "active low" this now
becomes a reset assertion
2) adding gpiod_set_value(reset, 0) after a delay to deassert reset
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
---
drivers/pci/controller/dwc/pci-dra7xx.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/pci/controller/dwc/pci-dra7xx.c b/drivers/pci/controller/dwc/pci-dra7xx.c
index dacd6da70c35..8dd20b394d0c 100644
--- a/drivers/pci/controller/dwc/pci-dra7xx.c
+++ b/drivers/pci/controller/dwc/pci-dra7xx.c
@@ -800,6 +800,8 @@ static int dra7xx_pcie_probe(struct platform_device *pdev)
dev_err(&pdev->dev, "gpio request failed, ret %d\n", ret);
goto err_gpio;
}
+ usleep_range(1000, 2000);
+ gpiod_set_value(reset, 0);
reg = dra7xx_pcie_readl(dra7xx, PCIECTRL_DRA7XX_CONF_DEVICE_CMD);
reg &= ~LTSSM_EN;
--
2.25.1
reply other threads:[~2021-05-17 15:57 UTC|newest]
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