2021-03-18 12:44:48

by Kiran Gunda

Subject: [PATCH V5 2/2] 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 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 <[email protected]>
Reviewed-by: Daniel Thompson <[email protected]>
---
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

2021-03-23 09:44:26

by Lee Jones

Subject: Re: [PATCH V5 2/2] backlight: qcom-wled: Correct the sync_toggle sequence

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 <[email protected]>
> Reviewed-by: Daniel Thompson <[email protected]>
> ---
> 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
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