linux-kernel - [PATCH] HID: core: add helper for finding a field with a certain usage

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Message-ID: <3EA8F21F-2C0A-49DB-BD23-224CE9D65A0D@live.com>
Date: Fri, 5 Jul 2024 11:17:42 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: Jiri Kosina <jikos@...nel.org>, "bentiss@...nel.org" <bentiss@...nel.org>
CC: "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>, Linux Kernel
 Mailing List <linux-kernel@...r.kernel.org>, Orlando Chamberlain
	<orlandoch.dev@...il.com>, Kerem Karabay <kekrby@...il.com>
Subject: [PATCH] HID: core: add helper for finding a field with a certain
 usage

From: Kerem Karabay <kekrby@...il.com>

This helper will allow HID drivers to easily determine if they should
bind to a hid_device by checking for the prescence of a certain field
when its ID is not enough, which can be the case on USB devices with
multiple interfaces and/or configurations.

Signed-off-by: Kerem Karabay <kekrby@...il.com>
Signed-off-by: Aditya Garg <gargaditya08@...e.com>
---
 drivers/hid/hid-core.c          | 25 +++++++++++++++++++++++++
 drivers/hid/hid-google-hammer.c | 27 ++-------------------------
 include/linux/hid.h             |  2 ++
 3 files changed, 29 insertions(+), 25 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 8992e3c1e..6395bdc2e 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1906,6 +1906,31 @@ int hid_set_field(struct hid_field *field, unsigned offset, __s32 value)
 }
 EXPORT_SYMBOL_GPL(hid_set_field);
 
+struct hid_field *hid_find_field(struct hid_device *hdev, unsigned int report_type,
+				 unsigned int application, unsigned int usage)
+{
+	struct list_head *report_list = &hdev->report_enum[report_type].report_list;
+	struct hid_report *report;
+	int i, j;
+
+	list_for_each_entry(report, report_list, list) {
+		if (report->application != application)
+			continue;
+
+		for (i = 0; i < report->maxfield; i++) {
+			struct hid_field *field = report->field[i];
+
+			for (j = 0; j < field->maxusage; j++) {
+				if (field->usage[j].hid == usage)
+					return field;
+			}
+		}
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(hid_find_field);
+
 static struct hid_report *hid_get_report(struct hid_report_enum *report_enum,
 		const u8 *data)
 {
diff --git a/drivers/hid/hid-google-hammer.c b/drivers/hid/hid-google-hammer.c
index c6bdb9c4e..fba3652aa 100644
--- a/drivers/hid/hid-google-hammer.c
+++ b/drivers/hid/hid-google-hammer.c
@@ -419,38 +419,15 @@ static int hammer_event(struct hid_device *hid, struct hid_field *field,
 	return 0;
 }
 
-static bool hammer_has_usage(struct hid_device *hdev, unsigned int report_type,
-			unsigned application, unsigned usage)
-{
-	struct hid_report_enum *re = &hdev->report_enum[report_type];
-	struct hid_report *report;
-	int i, j;
-
-	list_for_each_entry(report, &re->report_list, list) {
-		if (report->application != application)
-			continue;
-
-		for (i = 0; i < report->maxfield; i++) {
-			struct hid_field *field = report->field[i];
-
-			for (j = 0; j < field->maxusage; j++)
-				if (field->usage[j].hid == usage)
-					return true;
-		}
-	}
-
-	return false;
-}
-
 static bool hammer_has_folded_event(struct hid_device *hdev)
 {
-	return hammer_has_usage(hdev, HID_INPUT_REPORT,
+	return !!hid_find_field(hdev, HID_INPUT_REPORT,
 				HID_GD_KEYBOARD, HID_USAGE_KBD_FOLDED);
 }
 
 static bool hammer_has_backlight_control(struct hid_device *hdev)
 {
-	return hammer_has_usage(hdev, HID_OUTPUT_REPORT,
+	return !!hid_find_field(hdev, HID_OUTPUT_REPORT,
 				HID_GD_KEYBOARD, HID_AD_BRIGHTNESS);
 }
 
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 39e21e381..9520fdfdd 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -913,6 +913,8 @@ extern void hidinput_report_event(struct hid_device *hid, struct hid_report *rep
 extern int hidinput_connect(struct hid_device *hid, unsigned int force);
 extern void hidinput_disconnect(struct hid_device *);
 
+struct hid_field *hid_find_field(struct hid_device *hdev, unsigned int report_type,
+				 unsigned int application, unsigned int usage);
 int hid_set_field(struct hid_field *, unsigned, __s32);
 int hid_input_report(struct hid_device *hid, enum hid_report_type type, u8 *data, u32 size,
 		     int interrupt);
-- 
2.42.0