spi/pl022: Add high priority message pump support

This switches the PL022 worker to a kthread in order to get
hold of a mechanism to control the message pump priority. On
low-latency systems elevating the message kthread to realtime
priority give a real sleek response curve. This has been
confirmed by measurements. Realtime priority elevation for
a certain PL022 port can be requested from platform data.

Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-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>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/amba/pl022.h b/include/linux/amba/pl022.h
index 572f637299c9..3672f40f3455 100644
--- a/include/linux/amba/pl022.h
+++ b/include/linux/amba/pl022.h
@@ -241,6 +241,8 @@ struct dma_chan;
  * @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.
+ * @rt: indicates the controller should run the message pump with realtime
+ *     priority to minimise the transfer latency on the bus.
  */
 struct pl022_ssp_controller {
         u16 bus_id;
@@ -250,6 +252,7 @@ struct pl022_ssp_controller {
         void *dma_rx_param;
         void *dma_tx_param;
         int autosuspend_delay;
+        bool rt;
 };
 
 /**