Re: [PATCH V2 2/2] backlight: qcom-wled: Correct the sync_toggle sequence

[Daniel Thompson <daniel.thompson@linaro.org>]

On Fri, Feb 26, 2021 at 05:42:24PM +0530, Kiran Gunda wrote:
> As per the current implementation, after FSC (Full Scale Current)
> and brightness update the sync bits are transitioned from 1 to 0.

This still seems to incorrectly describe the current behaviour.

Surely in most cases (i.e. every time except the first) the value of the
sync bit is 0 when the function is called and we get both a 0 to 1
and then a 1 to 0 transition.

That is why I recommended set-then-clear terminology to describe the
current behaviour. It is concise and correct.


Daniel.



> But, the FSC and brightness sync takes place during a 0 to 1
> 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 <kgunda@codeaurora.org>
> ---
>  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
>