linux-kernel - [PATCH v2] HID: google: Get HID report on probe to confirm tablet switch state

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Date:   Fri, 15 Jan 2021 13:42:16 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Dmitry Torokhov <dtor@...omium.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] HID: google: Get HID report on probe to confirm tablet switch state

This forces reading the base folded state anytime the device is
probed, to make sure it's in sync.

This is useful after a reboot, if the device re-enumerates for
any reason (e.g. ESD shock), or if the driver is unbound/rebound
(debugging/testing).

Without this, the tablet switch state is only synchronized after a
key is pressed (since the device would then send a report that
includes the switch state), leading to strange UX (e.g. UI
mode changes when a key is pressed after reboot).

This is not a problem on detachable base attach, as the device,
by itself, sends a report after it is booted up.

Signed-off-by: Nicolas Boichat <drinkcat@...omium.org>
---
Instead of all this manual parsing, it'd be easier to just call:
hid_hw_request(hdev, report, HID_REQ_GET_REPORT);
However, that fails silently as hdev->driver_input_lock is held
during probe (or even some callbacks like input_configured.

Changes in v2:
 - Improve commit message description.

 drivers/hid/hid-google-hammer.c | 85 +++++++++++++++++++++++++--------
 1 file changed, 66 insertions(+), 19 deletions(-)

diff --git a/drivers/hid/hid-google-hammer.c b/drivers/hid/hid-google-hammer.c
index 85a054f1ce38..d9319622da44 100644
--- a/drivers/hid/hid-google-hammer.c
+++ b/drivers/hid/hid-google-hammer.c
@@ -392,30 +392,34 @@ static int hammer_input_mapping(struct hid_device *hdev, struct hid_input *hi,
 	return 0;
 }
 
-static int hammer_event(struct hid_device *hid, struct hid_field *field,
-			struct hid_usage *usage, __s32 value)
+static void hammer_folded_event(struct hid_device *hdev, bool folded)
 {
 	unsigned long flags;
 
-	if (usage->hid == HID_USAGE_KBD_FOLDED) {
-		spin_lock_irqsave(&cbas_ec_lock, flags);
+	spin_lock_irqsave(&cbas_ec_lock, flags);
 
-		/*
-		 * If we are getting events from Whiskers that means that it
-		 * is attached to the lid.
-		 */
-		cbas_ec.base_present = true;
-		cbas_ec.base_folded = value;
-		hid_dbg(hid, "%s: base: %d, folded: %d\n", __func__,
-			cbas_ec.base_present, cbas_ec.base_folded);
-
-		if (cbas_ec.input) {
-			input_report_switch(cbas_ec.input,
-					    SW_TABLET_MODE, value);
-			input_sync(cbas_ec.input);
-		}
+	/*
+	 * If we are getting events from Whiskers that means that it
+	 * is attached to the lid.
+	 */
+	cbas_ec.base_present = true;
+	cbas_ec.base_folded = folded;
+	hid_dbg(hdev, "%s: base: %d, folded: %d\n", __func__,
+		cbas_ec.base_present, cbas_ec.base_folded);
 
-		spin_unlock_irqrestore(&cbas_ec_lock, flags);
+	if (cbas_ec.input) {
+		input_report_switch(cbas_ec.input, SW_TABLET_MODE, folded);
+		input_sync(cbas_ec.input);
+	}
+
+	spin_unlock_irqrestore(&cbas_ec_lock, flags);
+}
+
+static int hammer_event(struct hid_device *hid, struct hid_field *field,
+			struct hid_usage *usage, __s32 value)
+{
+	if (usage->hid == HID_USAGE_KBD_FOLDED) {
+		hammer_folded_event(hid, value);
 		return 1; /* We handled this event */
 	}
 
@@ -457,6 +461,47 @@ static bool hammer_has_backlight_control(struct hid_device *hdev)
 				HID_GD_KEYBOARD, HID_AD_BRIGHTNESS);
 }
 
+static void hammer_get_folded_state(struct hid_device *hdev)
+{
+	struct hid_report *report;
+	char *buf;
+	int len, rlen;
+	int a;
+
+	report = hdev->report_enum[HID_INPUT_REPORT].report_id_hash[0x0];
+
+	if (!report || report->maxfield < 1)
+		return;
+
+	len = hid_report_len(report) + 1;
+
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf)
+		return;
+
+	rlen = hid_hw_raw_request(hdev, report->id, buf, len, report->type, HID_REQ_GET_REPORT);
+
+	if (rlen != len) {
+		hid_warn(hdev, "Unable to read base folded state: %d (expected %d)\n", rlen, len);
+		goto out;
+	}
+
+	for (a = 0; a < report->maxfield; a++) {
+		struct hid_field *field = report->field[a];
+
+		if (field->usage->hid == HID_USAGE_KBD_FOLDED) {
+			u32 value = hid_field_extract(hdev, buf+1,
+					field->report_offset, field->report_size);
+
+			hammer_folded_event(hdev, value);
+			break;
+		}
+	}
+
+out:
+	kfree(buf);
+}
+
 static int hammer_probe(struct hid_device *hdev,
 			const struct hid_device_id *id)
 {
@@ -481,6 +526,8 @@ static int hammer_probe(struct hid_device *hdev,
 		error = hid_hw_open(hdev);
 		if (error)
 			return error;
+
+		hammer_get_folded_state(hdev);
 	}
 
 	if (hammer_has_backlight_control(hdev)) {
-- 
2.30.0.284.gd98b1dd5eaa7-goog