[PATCH 06/10] media: microchip-isc: do not touch WB registers when not streaming

[Balakrishnan Sambath]

isc_s_awb_ctrl() called isc_update_awb_ctrls() unconditionally, writing
the white balance registers even when the device is runtime suspended;
on many ARM platforms accessing the unclocked registers is an external
abort. The write was also done without awb_lock, racing isc_awb_work(),
which holds it so the DMA done IRQ cannot latch a half-updated pipeline.

Write the registers only while streaming, under awb_lock, and update the
profile there. When not streaming the new gains and offsets stay cached
in the control state and are programmed by isc_configure() at the next
stream start.

Fixes: 91b4e487b0c6 ("media: microchip: add ISC driver as Microchip ISC")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Balakrishnan Sambath <balakrishnan.s@xxxxxxxxxxxxx>
---
 drivers/media/platform/microchip/microchip-isc-base.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/media/platform/microchip/microchip-isc-base.c b/drivers/media/platform/microchip/microchip-isc-base.c
index f7fbd3cd8edc..2911cfc660a0 100644
--- a/drivers/media/platform/microchip/microchip-isc-base.c
+++ b/drivers/media/platform/microchip/microchip-isc-base.c
@@ -1509,20 +1509,21 @@ static int isc_s_awb_ctrl(struct v4l2_ctrl *ctrl)
 		if (ctrl->cluster[ISC_CTRL_GB_OFF]->is_new)
 			ctrls->offset[ISC_HIS_CFG_MODE_GB] = isc->gb_off_ctrl->val;
 
-		isc_update_awb_ctrls(isc);
-
 		mutex_lock(&isc->awb_mutex);
 		if (vb2_is_streaming(&isc->vb2_vidq)) {
-			/*
-			 * If we are streaming, we can update profile to
-			 * have the new settings in place.
-			 */
+			unsigned long flags;
+
+			/* awb_lock serialises the WB writes against the IRQ */
+			spin_lock_irqsave(&isc->awb_lock, flags);
+			isc_update_awb_ctrls(isc);
+			spin_unlock_irqrestore(&isc->awb_lock, flags);
+
 			isc_update_profile(isc);
 		} else {
 			/*
-			 * The auto cluster will activate automatically this
-			 * control. This has to be deactivated when not
-			 * streaming.
+			 * Not streaming: keep the cached values for the next
+			 * stream start and deactivate the cluster-activated
+			 * do_white_balance button.
 			 */
 			v4l2_ctrl_activate(isc->do_wb_ctrl, false);
 		}

-- 
2.34.1