[PATCH] 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).

Only fetch the feature report from hardware on the first usage
(usage->usage_index == 0) 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>
---
 drivers/hid/hid-vivaldi-common.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/hid/hid-vivaldi-common.c b/drivers/hid/hid-vivaldi-common.c
index c3c9fe9e697b..cfee7be4d759 100644
--- a/drivers/hid/hid-vivaldi-common.c
+++ b/drivers/hid/hid-vivaldi-common.c
@@ -49,6 +49,12 @@ void vivaldi_feature_mapping(struct hid_device *hdev,
 	if (fn_key > data->num_function_row_keys)
 		data->num_function_row_keys = fn_key;
 
+	if (usage->usage_index) {
+		data->function_row_physmap[fn_key - MIN_FN_ROW_KEY] =
+			field->value[usage->usage_index];
+		return;
+	}
+
 	report_data = buf = hid_alloc_report_buf(report, GFP_KERNEL);
 	if (!report_data)
 		return;
-- 
2.56.0.385.gd3acb90ef8-goog