spi: spi-sun6i: enable autosuspend feature

If SPI is used for periodic polling any sensor, significant delays
sometimes appear. Switching on module clocks during resume lead to delays.
Enabling autosuspend mode causes the controller to not suspend between
SPI transfers and the delays disappear.

The commit also remove unnecessary call to pm_runtime_idle() used
to explicit put device to suspended state. Without pm_runtime_idle() PM
core will put device in the suspended state just after probe() returns.
Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20201019150343.2520-1-akochetkov@lintech.ruSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-sun6i.c

@@ -22,6 +22,8 @@
 
 #include <linux/spi/spi.h>
 
+#define SUN6I_AUTOSUSPEND_TIMEOUT	2000
+
 #define SUN6I_FIFO_DEPTH		128
 #define SUN8I_FIFO_DEPTH		64
 
@@ -650,9 +652,10 @@ static int sun6i_spi_probe(struct platform_device *pdev)
 		goto err_free_dma_rx;
 	}
 
+	pm_runtime_set_autosuspend_delay(&pdev->dev, SUN6I_AUTOSUSPEND_TIMEOUT);
+	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_active(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
-	pm_runtime_idle(&pdev->dev);
 
 	ret = devm_spi_register_master(&pdev->dev, master);
 	if (ret) {