[PATCH] spi: Add cond_resched() in main message processing loop

[Mark Brown <broonie@xxxxxxxxxx>]

When a controller has only PIO support it is very likely that we will
run into use cases where we spend a very large amount of time consuming
CPU.  Code that does this should call cond_resched() every once in a
while to give other tasks more of a chance to run so do that in the main
SPI loop, the overhead is negligable if it's not needed.

Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 drivers/spi/spi.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 0ad55946e388..4252a112985c 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1207,6 +1207,9 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
 		return;
 	}
 	mutex_unlock(&master->bus_lock_mutex);
+
+	/* Prod the scheduler in case transfer_one() was busy waiting */
+	cond_resched();
 }
 
 /**
-- 
2.7.0

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