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[1/2] HID: wacom: Support sequence numbers smaller than 16-bit

Message ID 20240909203208.47339-1-jason.gerecke@wacom.com
State New
Headers show
Series [1/2] HID: wacom: Support sequence numbers smaller than 16-bit | expand

Commit Message

Gerecke, Jason Sept. 9, 2024, 8:32 p.m. UTC 
From: Jason Gerecke <jason.gerecke@wacom.com>

The current dropped packet reporting assumes that all sequence numbers
are 16 bits in length. This results in misleading "Dropped" messages if
the hardware uses fewer bits. For example, if a tablet uses only 8 bits
to store its sequence number, once it rolls over from 255 -> 0, the
driver will still be expecting a packet "256". This patch adjusts the
logic to reset the next expected packet to logical_minimum whenever
it overflows beyond logical_maximum.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Tested-by: Joshua Dickens <joshua.dickens@wacom.com>
Fixes: 6d09085b38e5 ("HID: wacom: Adding Support for new usages")
---
 drivers/hid/wacom_wac.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Comments

Jiri Kosina Sept. 10, 2024, 9:48 p.m. UTC | #1 
On Tue, 10 Sep 2024, Jason Gerecke wrote:

> These are pretty minor fixes, so I agree that there is no urgent need
> to get them into 6.11. Feel free to queue them for 6.12 instead.

Thanks. Both now queued in hid.git#for-6.12/wacom.
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Patch

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 74258a78d0408..cef08737a6240 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -2512,9 +2512,14 @@  static void wacom_wac_pen_event(struct hid_device *hdev, struct hid_field *field
 		wacom_wac->hid_data.barrelswitch3 = value;
 		return;
 	case WACOM_HID_WD_SEQUENCENUMBER:
-		if (wacom_wac->hid_data.sequence_number != value)
-			hid_warn(hdev, "Dropped %hu packets", (unsigned short)(value - wacom_wac->hid_data.sequence_number));
+		if (wacom_wac->hid_data.sequence_number != value) {
+			int sequence_size = field->logical_maximum - field->logical_minimum + 1;
+			int drop_count = (value - wacom_wac->hid_data.sequence_number) % sequence_size;
+			hid_warn(hdev, "Dropped %d packets", drop_count);
+		}
 		wacom_wac->hid_data.sequence_number = value + 1;
+		if (wacom_wac->hid_data.sequence_number > field->logical_maximum)
+			wacom_wac->hid_data.sequence_number = field->logical_minimum;
 		return;
 	}