FAILED: patch "[PATCH] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 840b7a5edf88fe678c60dee88a135647c0ea4375
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024072923-grating-bobsled-30d0@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

840b7a5edf88 ("PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting ep_gpio") 58adbfb3ebec ("PCI: rockchip: Make 'ep-gpios' DT property optional")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 840b7a5edf88fe678c60dee88a135647c0ea4375 Mon Sep 17 00:00:00 2001
From: Manivannan Sadhasivam <[email protected]>
Date: Tue, 16 Apr 2024 11:12:35 +0530
Subject: [PATCH] PCI: rockchip: Use GPIOD_OUT_LOW flag while requesting
ep_gpio
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Rockchip platforms use 'GPIO_ACTIVE_HIGH' flag in the devicetree definition for ep_gpio. This means, whatever the logical value set by the driver for the ep_gpio, physical line will output the same logic level.

For instance,

gpiod_set_value_cansleep(rockchip->ep_gpio, 0); --> Level low gpiod_set_value_cansleep(rockchip->ep_gpio, 1); --> Level high

But while requesting the ep_gpio, GPIOD_OUT_HIGH flag is currently used. Now, this also causes the physical line to output 'high' creating trouble for endpoint devices during host reboot.

When host reboot happens, the ep_gpio will initially output 'low' due to the GPIO getting reset to its POR value. Then during host controller probe, it will output 'high' due to GPIOD_OUT_HIGH flag. Then during rockchip_pcie_host_init_port(), it will first output 'low' and then 'high' indicating the completion of controller initialization.

On the endpoint side, each output 'low' of ep_gpio is accounted for PERST# assert and 'high' for PERST# deassert. With the above mentioned flow during host reboot, endpoint will witness below state changes for PERST#:

(1) PERST# assert - GPIO POR state
(2) PERST# deassert - GPIOD_OUT_HIGH while requesting GPIO
(3) PERST# assert - rockchip_pcie_host_init_port()
(4) PERST# deassert - rockchip_pcie_host_init_port()

Now the time interval between (2) and (3) is very short as both happen during the driver probe(), and this results in a race in the endpoint. Because, before completing the PERST# deassertion in (2), endpoint got another PERST# assert in (3).

A proper way to fix this issue is to change the GPIOD_OUT_HIGH flag in (2) to GPIOD_OUT_LOW. Because the usual convention is to request the GPIO with a state corresponding to its 'initial/default' value and let the driver change the state of the GPIO when required.

As per that, the ep_gpio should be requested with GPIOD_OUT_LOW as it corresponds to the POR value of '0' (PERST# assert in the endpoint). Then the driver can change the state of the ep_gpio later in rockchip_pcie_host_init_port() as per the initialization sequence.

This fixes the firmware crash issue in Qcom based modems connected to Rockpro64 based board.

index 0ef2e622d36e..c07d7129f1c7 100644
@@ -121,7 +121,7 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
 
 	if (rockchip->is_rc) {
 		rockchip->ep_gpio = devm_gpiod_get_optional(dev, "ep",
-							    GPIOD_OUT_HIGH);
+							    GPIOD_OUT_LOW);
 		if (IS_ERR(rockchip->ep_gpio))
 			return dev_err_probe(dev, PTR_ERR(rockchip->ep_gpio),
 					     "failed to get ep GPIO\n");