[RFC v1 1/2] HID: logitech-hidpp: Fix "Sw. Id." for HID++ 2.0 commands

[Bastien Nocera <hadess@hadess.net>]

Always set a non-zero "Sw. Id." in the lower nibble of the Function/ASE
and Software Identifier byte in HID++ 2.0 commands.

As per the "Protocol HID++2.0 essential features" section in
https://lekensteyn.nl/files/logitech/logitech_hidpp_2.0_specification_draft_2012-06-04.pdf
"
Software identifier (4 bits, unsigned)

A number uniquely defining the software that sends a request. The
firmware must copy the software identifier in the response but does
not use it in any other ways.

0 Do not use (allows to distinguish a notification from a response).
"

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215699
Signed-off-by: Bastien Nocera <hadess@hadess.net>
---
 drivers/hid/hid-logitech-hidpp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index 86e7a38d8a9a..02f8c99672c7 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -41,6 +41,9 @@ module_param(disable_tap_to_click, bool, 0644);
 MODULE_PARM_DESC(disable_tap_to_click,
 	"Disable Tap-To-Click mode reporting for touchpads (only on the K400 currently).");
 
+/* Define a non-zero software ID to identify our own requests */
+#define LINUX_KERNEL_SW_ID			0x06
+
 #define REPORT_ID_HIDPP_SHORT			0x10
 #define REPORT_ID_HIDPP_LONG			0x11
 #define REPORT_ID_HIDPP_VERY_LONG		0x12
@@ -343,7 +346,7 @@ static int hidpp_send_fap_command_sync(struct hidpp_device *hidpp,
 	else
 		message->report_id = REPORT_ID_HIDPP_LONG;
 	message->fap.feature_index = feat_index;
-	message->fap.funcindex_clientid = funcindex_clientid;
+	message->fap.funcindex_clientid = funcindex_clientid | LINUX_KERNEL_SW_ID;
 	memcpy(&message->fap.params, params, param_count);
 
 	ret = hidpp_send_message_sync(hidpp, message, response);
-- 
2.37.2