spi: Add cond_resched() in main message processing loop

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 <[email protected]>
Signed-off-by: Mark Brown <[email protected]>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index dcc6f6e926688a162dcc5165d840328249eda077..0b2bbf14446078a0f6e7631d21a6e86a755db41a 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1184,6 +1184,9 @@ 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();
 }
 
 /**