spi: Refactor spi_stop_queue()

The refactoring makes code less verbose and easier to read.
Besides that the binary size is also reduced, which sounds
like a win-win case:

  add/remove: 0/1 grow/shrink: 2/2 up/down: 210/-226 (-16)
  Function                            old     new   delta
  spi_destroy_queue                    42     156    +114
  spi_controller_suspend              101     197     +96
  spi_unregister_controller           346     319     -27
  spi_register_controller            1834    1794     -40
  spi_stop_queue                      159       -    -159
  Total: Before=49230, After=49214, chg -0.03%
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://msgid.link/r/20240510204945.2581944-1-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -2219,11 +2219,8 @@ static int spi_start_queue(struct spi_controller *ctlr)
 
 static int spi_stop_queue(struct spi_controller *ctlr)
 {
+	unsigned int limit = 500;
 	unsigned long flags;
-	unsigned limit = 500;
-	int ret = 0;
-
-	spin_lock_irqsave(&ctlr->queue_lock, flags);
 
 	/*
 	 * This is a bit lame, but is optimized for the common execution path.
@@ -2231,20 +2228,18 @@ static int spi_stop_queue(struct spi_controller *ctlr)
 	 * execution path (pump_messages) would be required to call wake_up or
 	 * friends on every SPI message. Do this instead.
 	 */
-	while ((!list_empty(&ctlr->queue) || ctlr->busy) && limit--) {
+	do {
+		spin_lock_irqsave(&ctlr->queue_lock, flags);
+		if (list_empty(&ctlr->queue) && !ctlr->busy) {
+			ctlr->running = false;
+			spin_unlock_irqrestore(&ctlr->queue_lock, flags);
+			return 0;
+		}
 		spin_unlock_irqrestore(&ctlr->queue_lock, flags);
 		usleep_range(10000, 11000);
-		spin_lock_irqsave(&ctlr->queue_lock, flags);
-	}
-
-	if (!list_empty(&ctlr->queue) || ctlr->busy)
-		ret = -EBUSY;
-	else
-		ctlr->running = false;
+	} while (--limit);
 
-	spin_unlock_irqrestore(&ctlr->queue_lock, flags);
-
-	return ret;
+	return -EBUSY;
 }
 
 static int spi_destroy_queue(struct spi_controller *ctlr)