[PATCH v3] HID: vivaldi: avoid redundant feature report reads per usage

[Zhengping Jiang]

vivaldi_feature_mapping() is invoked by hidinput_configure_usages() in
ascending usage_index order for each usage in the top-row physical keymap
field. Because fetching the feature report at usage_index == 0 already
reads the entire report from hardware and populates field->value[] for all
usages in the field, calling hid_hw_raw_request() again for subsequent
usages redundantly reads the same report N times (e.g., 12 sequential BLE
GATT reads taking ~2s on Vivaldi BLE keyboards).

Fetch the feature report from hardware once per HID_USAGE_FN_ROW_PHYSMAP
field at usage_index == 0 before validating individual usage entries, and
reuse field->value[usage->usage_index] for subsequent usages in the field.

Fixes: 33bbe04a15f2 ("HID: google: extract Vivaldi hid feature mapping for use in hid-hammer")
Signed-off-by: Zhengping Jiang <jiangzp@xxxxxxxxxx>
---
Changes in v3:
- Add comment explaining why the report is only read at usage_index == 0
  and how failed reads rely on zero-initialized field->value[].
- Jump/fall through to parse_usage on read failure so usage_index == 0
  updates num_function_row_keys consistently with subsequent usages and
  preserves original behavior when only one usage is present.

Changes in v2:
- Move per-usage validation (HID_UP_ORDINAL and fn_key bounds) after the
  usage_index == 0 hardware read so the report is still fetched even if
  usage[0] is non-ordinal or out of bounds.

 drivers/hid/hid-vivaldi-common.c | 34 +++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/drivers/hid/hid-vivaldi-common.c b/drivers/hid/hid-vivaldi-common.c
index c3c9fe9e697b..2d85555289d8 100644
--- a/drivers/hid/hid-vivaldi-common.c
+++ b/drivers/hid/hid-vivaldi-common.c
@@ -33,21 +33,22 @@ void vivaldi_feature_mapping(struct hid_device *hdev,
 {
 	struct vivaldi_data *data = hid_get_drvdata(hdev);
 	struct hid_report *report = field->report;
-	u8 *report_data, *buf;
+	u8 *report_data, *buf = NULL;
 	u32 report_len;
 	unsigned int fn_key;
 	int ret;
 
-	if (field->logical != HID_USAGE_FN_ROW_PHYSMAP ||
-	    (usage->hid & HID_USAGE_PAGE) != HID_UP_ORDINAL)
+	if (field->logical != HID_USAGE_FN_ROW_PHYSMAP)
 		return;
 
-	fn_key = usage->hid & HID_USAGE;
-	if (fn_key < MIN_FN_ROW_KEY || fn_key > MAX_FN_ROW_KEY)
-		return;
-
-	if (fn_key > data->num_function_row_keys)
-		data->num_function_row_keys = fn_key;
+	/*
+	 * Read the feature report only at usage_index == 0, as a single read
+	 * populates field->value[] for all usages in the field. If the read
+	 * fails, subsequent usages will not re-read the report and will rely
+	 * on field->value[] being zero-initialized.
+	 */
+	if (usage->usage_index)
+		goto parse_usage;
 
 	report_data = buf = hid_alloc_report_buf(report, GFP_KERNEL);
 	if (!report_data)
@@ -72,7 +73,7 @@ void vivaldi_feature_mapping(struct hid_device *hdev,
 	if (ret < 0) {
 		dev_warn(&hdev->dev, "failed to fetch feature %d\n",
 			 field->report->id);
-		goto out;
+		goto parse_usage;
 	}
 
 	if (!report->id) {
@@ -86,11 +87,20 @@ void vivaldi_feature_mapping(struct hid_device *hdev,
 
 	ret = __hid_report_raw_event(hdev, HID_FEATURE_REPORT, report_data,
 				     report_len, report_len, 0);
-	if (ret) {
+	if (ret)
 		dev_warn(&hdev->dev, "failed to report feature %d\n",
 			 field->report->id);
+
+parse_usage:
+	if ((usage->hid & HID_USAGE_PAGE) != HID_UP_ORDINAL)
 		goto out;
-	}
+
+	fn_key = usage->hid & HID_USAGE;
+	if (fn_key < MIN_FN_ROW_KEY || fn_key > MAX_FN_ROW_KEY)
+		goto out;
+
+	if (fn_key > data->num_function_row_keys)
+		data->num_function_row_keys = fn_key;
 
 	data->function_row_physmap[fn_key - MIN_FN_ROW_KEY] =
 		field->value[usage->usage_index];
-- 
2.56.0.385.gd3acb90ef8-goog