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

kgunda
2021-03-01T08:47:30Z

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@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
>>