drm/mali-dp: Add writeback support for DP500.

Mali DP500 behaves differently from the rest of the Mali DP IP,
in that it does not have a one-shot mode and keeps writing the
content of the current frame to the provided memory area until
stopped. As a way of emulating the one-shot behaviour, we are
going to use the CVAL interrupt that is being raised at the
start of each frame, during prefetch phase, to act as End-of-Write
signal, but with a twist: we are going to disable the memory
write engine right after we're notified that it has been enabled,
using the knowledge that the bit controlling the enabling will
only be acted upon on the next vblank/prefetch.

CVAL interrupt will fire durint the next prefetch phase every time
the global CVAL bit gets set, so we need a state byte to track
the memory write enabling. We also need to pay attention during the
disabling of the memory write engine as that requires the CVAL bit
to be set in the control register, but we don't want to do that
during an atomic commit, as it will write into the hardware a partial
state.

Reviewed-by: Brian Starkey <brian.starkey@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/gpu/drm/arm/malidp_hw.h b/drivers/gpu/drm/arm/malidp_hw.h
index a242e97cf642..c479738b81af 100644
--- a/drivers/gpu/drm/arm/malidp_hw.h
+++ b/drivers/gpu/drm/arm/malidp_hw.h
@@ -178,7 +178,7 @@ struct malidp_hw {
 	long (*se_calc_mclk)(struct malidp_hw_device *hwdev,
 			     struct malidp_se_config *se_config,
 			     struct videomode *vm);
-	/**
+	/*
 	 * Enable writing to memory the content of the next frame
 	 * @param hwdev - malidp_hw_device structure containing the HW description
 	 * @param addrs - array of addresses for each plane
@@ -232,6 +232,9 @@ struct malidp_hw_device {
 	/* track the device PM state */
 	bool pm_suspended;
 
+	/* track the SE memory writeback state */
+	u8 mw_state;
+
 	/* size of memory used for rotating layers, up to two banks available */
 	u32 rotation_memory[2];
 };