# \[PATCH V5 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence

- Subsystems: FRAMEBUFFER LAYER, ARM/QUALCOMM MAILING LIST, BACKLIGHT CLASS/SUBSYSTEM, THE REST
- Maintainers: Helge Deller, Lee Jones, Daniel Thompson, Jingoo Han, Linus Torvalds
- Status: REVIEWED · 1 review, 1 by a maintainer (M Daniel Thompson)
- Reviewed.
- Revision v5 (5 revisions archived); 1 review trailer.
- List: linux-fbdev
- 2 messages, 2 authors
- Page: https://ratatoskr.run/linux-fbdev/2021/03/6306297/t

## \[PATCH V5 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence

- From: Kiran Gunda \<hidden\>
- Date: 2021-03-18 12:41:42 
- Message: https://ratatoskr.run/linux-fbdev/2021/03/6306297.md

```text
As per the current implementation, after FSC (Full Scale Current)
and brightness update the sync bits are set-then-cleared.
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>
Reviewed-by: Daniel Thompson <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 e9fbe24..7c02f87 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->sink_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->sink_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

```

## Re: \[PATCH V5 2/2\] backlight: qcom-wled: Correct the sync\_toggle sequence

- From: Lee Jones \<hidden\>
- Date: 2021-03-23 09:41:27 
- Message: https://ratatoskr.run/linux-fbdev/2021/03/6311943.md

```text
On Thu, 18 Mar 2021, Kiran Gunda wrote:

> As per the current implementation, after FSC (Full Scale Current)
> and brightness update the sync bits are set-then-cleared.
> 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>
> Reviewed-by: Daniel Thompson <redacted>
> ---
>  drivers/video/backlight/qcom-wled.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)

Applied, thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
```