linux-kernel - [PATCH] power: sequencing: qcom-wcn: explain why we need the WLAN

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Message-ID: <20241217130714.51406-1-brgl@bgdev.pl>
Date: Tue, 17 Dec 2024 14:07:14 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH] power: sequencing: qcom-wcn: explain why we need the WLAN_EN GPIO hack

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

With the recent rework of the PCI power control code, the workaround for
the wlan-enable GPIO - where we don't set a default (low) state in the
power sequencing driver, but instead request the pin as-is - should no
longer be needed but some platforms still fail to probe the WLAN
controller. This is caused by the Qcom PCIe controller and needs a
workaround in the controller driver so add a FIXME to eventually remove
the hack from this driver once this is done.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/power/sequencing/pwrseq-qcom-wcn.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/power/sequencing/pwrseq-qcom-wcn.c b/drivers/power/sequencing/pwrseq-qcom-wcn.c
index cc03b5aaa8f2..9d6a68ac719f 100644
--- a/drivers/power/sequencing/pwrseq-qcom-wcn.c
+++ b/drivers/power/sequencing/pwrseq-qcom-wcn.c
@@ -396,6 +396,14 @@ static int pwrseq_qcom_wcn_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(ctx->bt_gpio),
 				     "Failed to get the Bluetooth enable GPIO\n");
 
+	/*
+	 * FIXME: This should actually be GPIOD_OUT_LOW. The driver model can
+	 * correctly handle provider <-> consumer dependencies but there is a
+	 * known issue with Qcom PCIe controllers where, if the device is
+	 * powered off abrubtly (without controller driver noticing), the PCIe
+	 * link moves to link down state. Until the link-down handling is
+	 * addressed in the controller driver, we need to keep this workaround.
+	 */
 	ctx->wlan_gpio = devm_gpiod_get_optional(dev, "wlan-enable",
 						 GPIOD_ASIS);
 	if (IS_ERR(ctx->wlan_gpio))
-- 
2.45.2