spi/pl022: add support for pm_runtime autosuspend

Adds support for configuring the spi bus to use autosuspend for
runtime power management. This can reduce the latency in starting an
spi transfer by not suspending the device immediately following
completion of a transfer. If another transfer then takes place before
the autosuspend timeout, the call to resume the device can return
immediately rather than needing to risk sleeping in order to resume
the device.
Reviewed-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Chris Blair <chris.blair@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/spi/spi-pl022.c

@@ -1516,7 +1516,13 @@ static void pump_messages(struct work_struct *work)
 			/* nothing more to do - disable spi/ssp and power off */
 			writew((readw(SSP_CR1(pl022->virtbase)) &
 				(~SSP_CR1_MASK_SSE)), SSP_CR1(pl022->virtbase));
-			pm_runtime_put(&pl022->adev->dev);
+
+			if (pl022->master_info->autosuspend_delay > 0) {
+				pm_runtime_mark_last_busy(&pl022->adev->dev);
+				pm_runtime_put_autosuspend(&pl022->adev->dev);
+			} else {
+				pm_runtime_put(&pl022->adev->dev);
+			}
 		}
 		pl022->busy = false;
 		spin_unlock_irqrestore(&pl022->queue_lock, flags);
@@ -2247,7 +2253,17 @@ pl022_probe(struct amba_device *adev, const struct amba_id *id)
 	dev_dbg(dev, "probe succeeded\n");
 
 	/* let runtime pm put suspend */
-	pm_runtime_put(dev);
+	if (platform_info->autosuspend_delay > 0) {
+		dev_info(&adev->dev,
+			"will use autosuspend for runtime pm, delay %dms\n",
+			platform_info->autosuspend_delay);
+		pm_runtime_set_autosuspend_delay(dev,
+			platform_info->autosuspend_delay);
+		pm_runtime_use_autosuspend(dev);
+		pm_runtime_put_autosuspend(dev);
+	} else {
+		pm_runtime_put(dev);
+	}
 	return 0;
 
  err_spi_register:

include/linux/amba/pl022.h

@@ -238,6 +238,9 @@ struct dma_chan;
  * @enable_dma: if true enables DMA driven transfers.
  * @dma_rx_param: parameter to locate an RX DMA channel.
  * @dma_tx_param: parameter to locate a TX DMA channel.
+ * @autosuspend_delay: delay in ms following transfer completion before the
+ *     runtime power management system suspends the device. A setting of 0
+ *     indicates no delay and the device will be suspended immediately.
  */
 struct pl022_ssp_controller {
 	u16 bus_id;
@@ -246,6 +249,7 @@ struct pl022_ssp_controller {
 	bool (*dma_filter)(struct dma_chan *chan, void *filter_param);
 	void *dma_rx_param;
 	void *dma_tx_param;
+	int autosuspend_delay;
 };
 
 /**