[PATCH V2 1/2] backlight: qcom-wled: Fix FSC update issue for WLED5

[PATCH V2 1/2] backlight: qcom-wled: Fix FSC update issue for WLED5

[Kiran Gunda]

Currently, for WLED5, the FSC (Full scale current) setting is not
updated properly due to driver toggling the wrong register after
an FSC update.

On WLED5 we should only toggle the MOD_SYNC bit after a brightness
update. For an FSC update we need to toggle the SYNC bits instead.

Fix it by adopting the common wled3_sync_toggle() for WLED5 and
introducing new code to the brightness update path to compensate.

Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>
---
 drivers/video/backlight/qcom-wled.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
index 3bc7800..aef52b9 100644
--- a/drivers/video/backlight/qcom-wled.c
+++ b/drivers/video/backlight/qcom-wled.c
@@ -348,7 +348,7 @@ static int wled3_sync_toggle(struct wled *wled)
 	return rc;
 }
 
-static int wled5_sync_toggle(struct wled *wled)
+static int wled5_mod_sync_toggle(struct wled *wled)
 {
 	int rc;
 	u8 val;
@@ -445,10 +445,23 @@ static int wled_update_status(struct backlight_device *bl)
 			goto unlock_mutex;
 		}
 
-		rc = wled->wled_sync_toggle(wled);
-		if (rc < 0) {
-			dev_err(wled->dev, "wled sync failed rc:%d\n", rc);
-			goto unlock_mutex;
+		if (wled->version < 5) {
+			rc = wled->wled_sync_toggle(wled);
+			if (rc < 0) {
+				dev_err(wled->dev, "wled sync failed rc:%d\n", rc);
+				goto unlock_mutex;
+			}
+		} else {
+			/*
+			 * For WLED5 toggling the MOD_SYNC_BIT updates the
+			 * brightness
+			 */
+			rc = wled5_mod_sync_toggle(wled);
+			if (rc < 0) {
+				dev_err(wled->dev, "wled mod sync failed rc:%d\n",
+					rc);
+				goto unlock_mutex;
+			}
 		}
 	}
 
@@ -1459,7 +1472,7 @@ static int wled_configure(struct wled *wled)
 		size = ARRAY_SIZE(wled5_opts);
 		*cfg = wled5_config_defaults;
 		wled->wled_set_brightness = wled5_set_brightness;
-		wled->wled_sync_toggle = wled5_sync_toggle;
+		wled->wled_sync_toggle = wled3_sync_toggle;
 		wled->wled_cabc_config = wled5_cabc_config;
 		wled->wled_ovp_delay = wled5_ovp_delay;
 		wled->wled_auto_detection_required =
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
 a Linux Foundation Collaborative Project

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

[Kiran Gunda]

As per the current implementation, after FSC (Full Scale Current)
and brightness update the sync bits are transitioned from 1 to 0.
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

Re: [PATCH V2 1/2] backlight: qcom-wled: Fix FSC update issue for WLED5

[Daniel Thompson]

On Fri, Feb 26, 2021 at 05:42:23PM +0530, Kiran Gunda wrote:
> Currently, for WLED5, the FSC (Full scale current) setting is not
> updated properly due to driver toggling the wrong register after
> an FSC update.
> 
> On WLED5 we should only toggle the MOD_SYNC bit after a brightness
> update. For an FSC update we need to toggle the SYNC bits instead.
> 
> Fix it by adopting the common wled3_sync_toggle() for WLED5 and
> introducing new code to the brightness update path to compensate.
> 
> Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.

> ---
>  drivers/video/backlight/qcom-wled.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> index 3bc7800..aef52b9 100644
> --- a/drivers/video/backlight/qcom-wled.c
> +++ b/drivers/video/backlight/qcom-wled.c
> @@ -348,7 +348,7 @@ static int wled3_sync_toggle(struct wled *wled)
>  	return rc;
>  }
>  
> -static int wled5_sync_toggle(struct wled *wled)
> +static int wled5_mod_sync_toggle(struct wled *wled)
>  {
>  	int rc;
>  	u8 val;
> @@ -445,10 +445,23 @@ static int wled_update_status(struct backlight_device *bl)
>  			goto unlock_mutex;
>  		}
>  
> -		rc = wled->wled_sync_toggle(wled);
> -		if (rc < 0) {
> -			dev_err(wled->dev, "wled sync failed rc:%d\n", rc);
> -			goto unlock_mutex;
> +		if (wled->version < 5) {
> +			rc = wled->wled_sync_toggle(wled);
> +			if (rc < 0) {
> +				dev_err(wled->dev, "wled sync failed rc:%d\n", rc);
> +				goto unlock_mutex;
> +			}
> +		} else {
> +			/*
> +			 * For WLED5 toggling the MOD_SYNC_BIT updates the
> +			 * brightness
> +			 */
> +			rc = wled5_mod_sync_toggle(wled);
> +			if (rc < 0) {
> +				dev_err(wled->dev, "wled mod sync failed rc:%d\n",
> +					rc);
> +				goto unlock_mutex;
> +			}
>  		}
>  	}
>  
> @@ -1459,7 +1472,7 @@ static int wled_configure(struct wled *wled)
>  		size = ARRAY_SIZE(wled5_opts);
>  		*cfg = wled5_config_defaults;
>  		wled->wled_set_brightness = wled5_set_brightness;
> -		wled->wled_sync_toggle = wled5_sync_toggle;
> +		wled->wled_sync_toggle = wled3_sync_toggle;
>  		wled->wled_cabc_config = wled5_cabc_config;
>  		wled->wled_ovp_delay = wled5_ovp_delay;
>  		wled->wled_auto_detection_required =
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>  a Linux Foundation Collaborative Project
> 

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

[Daniel Thompson]

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
> 

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

[kgunda]

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
>> 

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

[Daniel Thompson]

On Mon, Mar 01, 2021 at 02:15:12PM +0530, kgunda@codeaurora.org wrote:
> 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.
>
> 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.

Yes please.

In my original review I took time to explain why patch descriptions
require care and attention and, also, why expressing the original behaviour
as 1 to 0 was inadequate. Based on the previous feedback (and reply) I
was rather surprised that the problem was only half corrected in the
next revision.


Daniel.