linux-kernel - [PATCH 06/10] HID: surface-hid: Add support for hot-removal

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Date:   Fri, 20 May 2022 20:34:18 +0200
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>, Jiri Kosina <jikos@...nel.org>
Cc:     Maximilian Luz <luzmaximilian@...il.com>,
        Mark Gross <markgross@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        platform-driver-x86@...r.kernel.org, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 06/10] HID: surface-hid: Add support for hot-removal

Add support for hot-removal of SSAM HID client devices.

Once a device has been hot-removed, further communication with it should
be avoided as it may fail and time out. While the device will be removed
as soon as we detect hot-removal, communication may still occur during
teardown, especially when unregistering notifiers.

While hot-removal is a surprise event that can happen at any time, try
to avoid communication as much as possible once it has been detected to
prevent timeouts that can slow down device removal and cause issues,
e.g. when quickly re-attaching the device.

Signed-off-by: Maximilian Luz <luzmaximilian@...il.com>
---
 drivers/hid/surface-hid/surface_hid_core.c | 38 +++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/surface-hid/surface_hid_core.c b/drivers/hid/surface-hid/surface_hid_core.c
index e46330b2e561..87637f813de2 100644
--- a/drivers/hid/surface-hid/surface_hid_core.c
+++ b/drivers/hid/surface-hid/surface_hid_core.c
@@ -19,12 +19,30 @@
 #include "surface_hid_core.h"
 
 
+/* -- Utility functions. ---------------------------------------------------- */
+
+static bool surface_hid_is_hot_removed(struct surface_hid_device *shid)
+{
+	/*
+	 * Non-ssam client devices, i.e. platform client devices, cannot be
+	 * hot-removed.
+	 */
+	if (!is_ssam_device(shid->dev))
+		return false;
+
+	return ssam_device_is_hot_removed(to_ssam_device(shid->dev));
+}
+
+
 /* -- Device descriptor access. --------------------------------------------- */
 
 static int surface_hid_load_hid_descriptor(struct surface_hid_device *shid)
 {
 	int status;
 
+	if (surface_hid_is_hot_removed(shid))
+		return -ENODEV;
+
 	status = shid->ops.get_descriptor(shid, SURFACE_HID_DESC_HID,
 			(u8 *)&shid->hid_desc, sizeof(shid->hid_desc));
 	if (status)
@@ -61,6 +79,9 @@ static int surface_hid_load_device_attributes(struct surface_hid_device *shid)
 {
 	int status;
 
+	if (surface_hid_is_hot_removed(shid))
+		return -ENODEV;
+
 	status = shid->ops.get_descriptor(shid, SURFACE_HID_DESC_ATTRS,
 			(u8 *)&shid->attrs, sizeof(shid->attrs));
 	if (status)
@@ -88,9 +109,18 @@ static int surface_hid_start(struct hid_device *hid)
 static void surface_hid_stop(struct hid_device *hid)
 {
 	struct surface_hid_device *shid = hid->driver_data;
+	bool hot_removed;
+
+	/*
+	 * Communication may fail for devices that have been hot-removed. This
+	 * also includes unregistration of HID events, so we need to check this
+	 * here. Only if the device has not been marked as hot-removed, we can
+	 * safely disable events.
+	 */
+	hot_removed = surface_hid_is_hot_removed(shid);
 
 	/* Note: This call will log errors for us, so ignore them here. */
-	ssam_notifier_unregister(shid->ctrl, &shid->notif);
+	__ssam_notifier_unregister(shid->ctrl, &shid->notif, !hot_removed);
 }
 
 static int surface_hid_open(struct hid_device *hid)
@@ -109,6 +139,9 @@ static int surface_hid_parse(struct hid_device *hid)
 	u8 *buf;
 	int status;
 
+	if (surface_hid_is_hot_removed(shid))
+		return -ENODEV;
+
 	buf = kzalloc(len, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
@@ -126,6 +159,9 @@ static int surface_hid_raw_request(struct hid_device *hid, unsigned char reportn
 {
 	struct surface_hid_device *shid = hid->driver_data;
 
+	if (surface_hid_is_hot_removed(shid))
+		return -ENODEV;
+
 	if (rtype == HID_OUTPUT_REPORT && reqtype == HID_REQ_SET_REPORT)
 		return shid->ops.output_report(shid, reportnum, buf, len);
 
-- 
2.36.1