dell-laptop: Clear buffer before each SMBIOS call

Make sure that before initializing SMBIOS call, the input buffer does
not contain any garbage (e.g. values from previous SMBIOS call). This
fixes problems with passing undefined/random parameters to SMBIOS
functions.
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>

drivers/platform/x86/dell-laptop.c

@@ -311,10 +311,15 @@ static DEFINE_MUTEX(buffer_mutex);
 
 static int hwswitch_state;
 
+static void clear_buffer(void)
+{
+	memset(buffer, 0, sizeof(struct calling_interface_buffer));
+}
+
 static void get_buffer(void)
 {
 	mutex_lock(&buffer_mutex);
-	memset(buffer, 0, sizeof(struct calling_interface_buffer));
+	clear_buffer();
 }
 
 static void release_buffer(void)
@@ -558,6 +563,8 @@ static int dell_rfkill_set(void *data, bool blocked)
 	    !(buffer->output[1] & BIT(16)))
 		disable = 1;
 
+	clear_buffer();
+
 	buffer->input[0] = (1 | (radio<<8) | (disable << 16));
 	dell_send_request(buffer, 17, 11);
 
@@ -572,6 +579,7 @@ static void dell_rfkill_update_sw_state(struct rfkill *rfkill, int radio,
 	if (status & BIT(0)) {
 		/* Has hw-switch, sync sw_state to BIOS */
 		int block = rfkill_blocked(rfkill);
+		clear_buffer();
 		buffer->input[0] = (1 | (radio << 8) | (block << 16));
 		dell_send_request(buffer, 17, 11);
 	} else {
@@ -774,6 +782,7 @@ static int __init dell_setup_rfkill(void)
 	get_buffer();
 	dell_send_request(buffer, 17, 11);
 	status = buffer->output[1];
+	clear_buffer();
 	buffer->input[0] = 0x2;
 	dell_send_request(buffer, 17, 11);
 	hwswitch_state = buffer->output[1];