linux-kernel - [PATCH 2/3] PCI/pwrctrl: Add appropriate delays for slot power/clocks

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Message-Id: <20251219172222.2808195-2-sean.anderson@linux.dev>
Date: Fri, 19 Dec 2025 12:22:21 -0500
From: Sean Anderson <sean.anderson@...ux.dev>
To: Manivannan Sadhasivam <mani@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Bartosz Golaszewski <brgl@...nel.org>
Cc: linux-pci@...r.kernel.org,
	Chen-Yu Tsai <wenst@...omium.org>,
	linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>,
	Brian Norris <briannorris@...omium.org>,
	Niklas Cassel <cassel@...nel.org>,
	Chen-Yu Tsai <wens@...nel.org>,
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
	Alex Elder <elder@...cstar.com>,
	Sean Anderson <sean.anderson@...ux.dev>
Subject: [PATCH 2/3] PCI/pwrctrl: Add appropriate delays for slot power/clocks

Each of the PCIe electromechanical specifications requires a delay
between when power and clocks are stable and when PERST is released.
Delay for the specified time before continuing with initialization. If
there are no power supplies/clock, skip the associated delay as we
assume that they have been initialized by the bootloader (and that
booting up to this point has taken longer than the delay).

Signed-off-by: Sean Anderson <sean.anderson@...ux.dev>
---

 drivers/pci/pwrctrl/slot.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/pci/pwrctrl/slot.c b/drivers/pci/pwrctrl/slot.c
index 3320494b62d8..1c56fcd49f2b 100644
--- a/drivers/pci/pwrctrl/slot.c
+++ b/drivers/pci/pwrctrl/slot.c
@@ -5,6 +5,7 @@
  */
 
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
@@ -31,6 +32,7 @@ static int pci_pwrctrl_slot_probe(struct platform_device *pdev)
 {
 	struct pci_pwrctrl_slot_data *slot;
 	struct device *dev = &pdev->dev;
+	unsigned long delay = 0;
 	struct clk *clk;
 	int ret;
 
@@ -64,6 +66,17 @@ static int pci_pwrctrl_slot_probe(struct platform_device *pdev)
 				     "Failed to enable slot clock\n");
 	}
 
+	if (slot->num_supplies)
+		/*
+		 * Delay for T_PVPERL. This could be reduced to 1 ms/50 ms
+		 * (T_PVPGL) for Mini/M.2 slots.
+		 */
+		delay = 100000;
+	else if (clk)
+		/* Delay for T_PERST-CLK (100 us for all slot types) */
+		delay = 100;
+
+	fsleep(delay)
 	pci_pwrctrl_init(&slot->ctx, dev);
 
 	ret = devm_pci_pwrctrl_device_set_ready(dev, &slot->ctx);
-- 
2.35.1.1320.gc452695387.dirty