[PATCH v4 05/10] media: microchip-isc: do not touch WB registers when not streaming

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 and not stopping, under
awb_lock, and update the profile there. The isc->stop check covers the
window where isc_stop_streaming() has gated the clocks but vb2 still
reports streaming. Otherwise the new values stay cached and
isc_configure() programs them at the next stream start.

Fixes: 4e52889f48fe ("media: atmel: atmel-isc-base: expose white balance as v4l2 controls")
Cc: [email protected]
Signed-off-by: Balakrishnan Sambath <[email protected]>
---
 .../media/platform/microchip/microchip-isc-base.c    | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/media/platform/microchip/microchip-isc-base.c b/drivers/media/platform/microchip/microchip-isc-base.c
index 54f3093e14fc..3ea38da0e2aa 100644
--- a/drivers/media/platform/microchip/microchip-isc-base.c
+++ b/drivers/media/platform/microchip/microchip-isc-base.c
@@ -1509,20 +1509,24 @@ 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 (vb2_is_streaming(&isc->vb2_vidq) && !isc->stop) {
+			unsigned long flags;
+
 			/*
-			 * If we are streaming, we can update profile to
-			 * have the new settings in place.
+			 * awb_lock keeps the DMA done IRQ from latching a
+			 * partially written WB pipeline.
 			 */
+			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