[PATCH v2 2/2] dell-wmi: Process only one event on devices with interface version 0

["Pali Rohár" <pali.rohar@gmail.com>]

BIOS/ACPI on devices with WMI interface version 0 does not clear buffer
before filling it. So next time when BIOS/ACPI send WMI event which is
smaller as previous then it contains garbage in buffer from previous event.

BIOS/ACPI on devices with WMI interface version 1 clears buffer and
sometimes send more events in buffer at one call.

Since commit 83fc44c32ad8 ("dell-wmi: Update code for processing WMI
events") dell-wmi process all events in buffer (and not just first).

So to prevent reading garbage from buffer we will process only first one
event on devices with WMI interface version 0.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
---
 drivers/platform/x86/dell-wmi.c |   16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
index 1ad7a7b..5db9efb 100644
--- a/drivers/platform/x86/dell-wmi.c
+++ b/drivers/platform/x86/dell-wmi.c
@@ -237,6 +237,22 @@ static void dell_wmi_notify(u32 value, void *context)
 
 	buffer_end = buffer_entry + buffer_size;
 
+	/*
+	 * BIOS/ACPI on devices with WMI interface version 0 does not clear
+	 * buffer before filling it. So next time when BIOS/ACPI send WMI event
+	 * which is smaller as previous then it contains garbage in buffer from
+	 * previous event.
+	 *
+	 * BIOS/ACPI on devices with WMI interface version 1 clears buffer and
+	 * sometimes send more events in buffer at one call.
+	 *
+	 * So to prevent reading garbage from buffer we will process only first
+	 * one event on devices with WMI interface version 0.
+	 */
+	if (dell_wmi_interface_version == 0 && buffer_entry < buffer_end)
+		if (buffer_end > buffer_entry + buffer_entry[0] + 1)
+			buffer_end = buffer_entry + buffer_entry[0] + 1;
+
 	while (buffer_entry < buffer_end) {
 
 		len = buffer_entry[0];
-- 
1.7.9.5