linux-kernel - Re: [PATCH V1 2/2] backlight: qcom-wled: Correct the sync

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Message-ID: <427d82a0baa7ec1c3232469e81daa9a0@codeaurora.org>
Date:   Fri, 26 Feb 2021 12:10:52 +0530
From:   kgunda@...eaurora.org
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     bjorn.andersson@...aro.org, jingoohan1@...il.com,
        lee.jones@...aro.org, b.zolnierkie@...sung.com,
        dri-devel@...ts.freedesktop.org, jacek.anaszewski@...il.com,
        pavel@....cz, robh+dt@...nel.org, mark.rutland@....com,
        linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-fbdev@...r.kernel.org,
        phone-devel@...r.kernel.org
Subject: Re: [PATCH V1 2/2] backlight: qcom-wled: Correct the sync_toggle
 sequence

On 2021-02-24 16:56, Daniel Thompson wrote:
> On Wed, Feb 24, 2021 at 09:20:48AM +0530, Kiran Gunda wrote:
>> Currently the FSC SYNC_BIT and MOD_SYNC_BIT are toggled
>> from 1 to 0 to update the FSC and brightenss settings.
>> Change this sequence form 0 to 1 as per the hardware team
>> recommendation to update the FSC and brightness correctly.
> 
> Again... this patch description feels somewhat rushed. A patch
> description is there to support code reviewer and to go on the version
> history to assist with future maintainance. They matter!
> 
> Anyhow I don't recognise the "from 1 to 0" in the code since both 
> before
> an after the change it goes "from 0 to 1" and "from 1 to 0" but in a
> different order. Doesn't the code actually currently implement "set 
> then
> clear"? If so then, likewise the new code is adopting "clear then set".
> 
I would have used "set" and "clear" instead of "0" and "1".
Yes. The current code implementation is "set" all SYN bits and then 
"clear"
all SYNC bits. The new code is modified to change the sequence from 
"clear"
first and then "set" to ensure both FSC and brightness are updated.

> As with patch 1, the sync bits modified by wled3_sync_toggle singular
> or plural?
It is plural. We have to "clear" and "set" all sync bits.
> 
> Finally a description that is more sympathetic to the reviewer would be
> welcome.  For example the following (if my guess is right and it is
> true) makes things much easier for the reviewer:
> Sure. I will update the documentation and patch description clearly.
>   "The 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".
> 
> 
> Daniel.
> 
> 
>> 
>> Signed-off-by: Kiran Gunda <kgunda@...eaurora.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
>>