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

Daniel Thompson
2021-02-26T17:27:49Z

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
>