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

[kgunda@xxxxxxxxxxxxxx]

On 2021-02-26 22:56, Daniel Thompson wrote:
> 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.
Okay. Actually I have mentioned the "clear-and-set" in explaining the 
fix.
Let me modify the same terminology in explaining the problem case also.

> > 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@xxxxxxxxxxxxxx>
> > ---
> >  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