backlight: qcom-wled: Correct the sync_toggle sequence

As per the current implementation, after FSC (Full Scale Current)
and brightness update the sync bits are transitioned from set-then-clear.
But, the FSC and brightness sync takes place during a clear-then-set
transition of the sync bits. So the hardware team recommends a
clear-then-set approach in order to guarantee such a transition
regardless of the previous register state.

Signed-off-by: Kiran Gunda <redacted>
---
 drivers/video/backlight/qcom-wled.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index aef52b9..19f83ac 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c

@@ -337,13 +337,13 @@ static int wled3_sync_toggle(struct wled *wled)
 
 	rc = regmap_update_bits(wled->regmap,
 				wled->ctrl_addr + WLED3_SINK_REG_SYNC,
-				mask, mask);
+				mask, WLED3_SINK_REG_SYNC_CLEAR);
 	if (rc < 0)
 		return rc;
 
 	rc = regmap_update_bits(wled->regmap,
 				wled->ctrl_addr + WLED3_SINK_REG_SYNC,
-				mask, WLED3_SINK_REG_SYNC_CLEAR);
+				mask, mask);
 
 	return rc;
 }

@@ -353,17 +353,17 @@ static int wled5_mod_sync_toggle(struct wled *wled)
 	int rc;
 	u8 val;
 
-	val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT :
-					     WLED5_SINK_REG_SYNC_MOD_B_BIT;
 	rc = regmap_update_bits(wled->regmap,
 				wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT,
-				WLED5_SINK_REG_SYNC_MASK, val);
+				WLED5_SINK_REG_SYNC_MASK, 0);
 	if (rc < 0)
 		return rc;
 
+	val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT :
+					     WLED5_SINK_REG_SYNC_MOD_B_BIT;
 	return regmap_update_bits(wled->regmap,
 				  wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT,
-				  WLED5_SINK_REG_SYNC_MASK, 0);
+				  WLED5_SINK_REG_SYNC_MASK, val);
 }
 
 static int wled_ovp_fault_status(struct wled *wled, bool *fault_set)

-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
 a Linux Foundation Collaborative Project

On Mon, Mar 01, 2021 at 02:58:36PM +0530, Kiran Gunda wrote:

As per the current implementation, after FSC (Full Scale Current)
and brightness update the sync bits are transitioned from set-then-clear.

This does not makes sense since there are too many verbs. Set and clear
are both verbs so in this context: "the code will set the bit and then
the code will clear the bit".

Either:

s/transitioned from set-then-clear/set-then-cleared/.

Or:

s/transitioned from set-then-clear/using a set-then-clear approach/.

But, the FSC and brightness sync takes place during a clear-then-set
transition of the sync bits.

Likewise this no longer makes sense and had also become misleading.
Two changes of state, clear and then set, do not usually result in a
single transition.

Either:

s/clear-then-set/0 to 1/

Alternatively, if you want to stick exclusively to the set/clear
terminology then replace the whole quoted section with:

  But, the FSC and brightness sync takes place when the sync bits are
  set (e.g. on a rising edge).

So the hardware team recommends a
clear-then-set approach in order to guarantee such a transition
regardless of the previous register state.

Signed-off-by: Kiran Gunda <redacted>

With one of each of the changes proposed above:
Reviewed-by: Daniel Thompson <redacted>


Daniel.

10 more quoted lines

On 2021-03-01 15:32, Daniel Thompson wrote:

On Mon, Mar 01, 2021 at 02:58:36PM +0530, Kiran Gunda wrote:

quoted

As per the current implementation, after FSC (Full Scale Current)
and brightness update the sync bits are transitioned from set-then-clear.

This does not makes sense since there are too many verbs. Set and clear
are both verbs so in this context: "the code will set the bit and then
the code will clear the bit".

Either:

s/transitioned from set-then-clear/set-then-cleared/.

Or:

s/transitioned from set-then-clear/using a set-then-clear approach/.

quoted

But, the FSC and brightness sync takes place during a clear-then-set
transition of the sync bits.

Likewise this no longer makes sense and had also become misleading.
Two changes of state, clear and then set, do not usually result in a
single transition.

Either:

s/clear-then-set/0 to 1/

Alternatively, if you want to stick exclusively to the set/clear
terminology then replace the whole quoted section with:

  But, the FSC and brightness sync takes place when the sync bits are
  set (e.g. on a rising edge).

quoted

So the hardware team recommends a
clear-then-set approach in order to guarantee such a transition
regardless of the previous register state.

Signed-off-by: Kiran Gunda <redacted>

6 more quoted lines

Apologies for the mistake. I have corrected and submitted the
V4 series with the "reviewed-by" tag.

quoted

---
 drivers/video/backlight/qcom-wled.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index aef52b9..19f83ac 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c

@@ -337,13 +337,13 @@ static int wled3_sync_toggle(struct wled *wled)

 	rc = regmap_update_bits(wled->regmap,
 				wled->ctrl_addr + WLED3_SINK_REG_SYNC,
-				mask, mask);
+				mask, WLED3_SINK_REG_SYNC_CLEAR);
 	if (rc < 0)
 		return rc;

 	rc = regmap_update_bits(wled->regmap,
 				wled->ctrl_addr + WLED3_SINK_REG_SYNC,
-				mask, WLED3_SINK_REG_SYNC_CLEAR);
+				mask, mask);

 	return rc;
 }

@@ -353,17 +353,17 @@ static int wled5_mod_sync_toggle(struct wled *wled)
 	int rc;
 	u8 val;

-	val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT :
-					     WLED5_SINK_REG_SYNC_MOD_B_BIT;
 	rc = regmap_update_bits(wled->regmap,
 				wled->sink_addr + WLED5_SINK_REG_MOD_SYNC_BIT,
-				WLED5_SINK_REG_SYNC_MASK, val);
+				WLED5_SINK_REG_SYNC_MASK, 0);
 	if (rc < 0)
 		return rc;

+	val = (wled->cfg.mod_sel == MOD_A) ? WLED5_SINK_REG_SYNC_MOD_A_BIT :
+					     WLED5_SINK_REG_SYNC_MOD_B_BIT;

11 more quoted lines