Message-ID: <82fa847760309cb3382bf0a8da50162c@codeaurora.org>
Date:   Thu, 17 May 2018 15:17:34 +0530
From:   kgunda@...eaurora.org
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-leds@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH V1 2/5] backlight: qcom-wled: Add support for WLED4
 peripheral

On 2018-05-08 15:55, kgunda@...eaurora.org wrote:
> On 2018-05-07 21:50, Bjorn Andersson wrote:
>> On Thu 03 May 02:57 PDT 2018, Kiran Gunda wrote:
>> 
>>> WLED4 peripheral is present on some PMICs like pmi8998
>>> and pm660l. It has a different register map and also
>>> configurations are different. Add support for it.
>>> 
>> 
>> Several things are going on in this patch, it needs to be split to
>> not hide the functional changes from the structural/renames.
>> 
> Ok. I will split it in the next series.
>>> Signed-off-by: Kiran Gunda <kgunda@...eaurora.org>
>>> ---
>>>  .../bindings/leds/backlight/qcom-wled.txt          | 172 ++++-
>>>  drivers/video/backlight/qcom-wled.c                | 749 
>>> +++++++++++++++------
>>>  2 files changed, 696 insertions(+), 225 deletions(-)
>>> 
>>> diff --git 
>>> a/Documentation/devicetree/bindings/leds/backlight/qcom-wled.txt 
>>> b/Documentation/devicetree/bindings/leds/backlight/qcom-wled.txt
>>> index fb39e32..0ceffa1 100644
>>> --- a/Documentation/devicetree/bindings/leds/backlight/qcom-wled.txt
>>> +++ b/Documentation/devicetree/bindings/leds/backlight/qcom-wled.txt
>>> @@ -1,30 +1,129 @@
>>>  Binding for Qualcomm Technologies, Inc. WLED driver
>>> 
>>> -Required properties:
>>> -- compatible: should be "qcom,pm8941-wled"
>>> -- reg: slave address
>>> -
>>> -Optional properties:
>>> -- default-brightness: brightness value on boot, value from: 0-4095
>>> -	default: 2048
>>> -- label: The name of the backlight device
>>> -- qcom,cs-out: bool; enable current sink output
>>> -- qcom,cabc: bool; enable content adaptive backlight control
>>> -- qcom,ext-gen: bool; use externally generated modulator signal to 
>>> dim
>>> -- qcom,current-limit: mA; per-string current limit; value from 0 to 
>>> 25
>>> -	default: 20mA
>>> -- qcom,current-boost-limit: mA; boost current limit; one of:
>>> -	105, 385, 525, 805, 980, 1260, 1400, 1680
>>> -	default: 805mA
>>> -- qcom,switching-freq: kHz; switching frequency; one of:
>>> -	600, 640, 685, 738, 800, 872, 960, 1066, 1200, 1371,
>>> -	1600, 1920, 2400, 3200, 4800, 9600,
>>> -	default: 1600kHz
>>> -- qcom,ovp: V; Over-voltage protection limit; one of:
>>> -	27, 29, 32, 35
>>> -	default: 29V
>>> -- qcom,num-strings: #; number of led strings attached; value from 1 
>>> to 3
>>> -	default: 2
>>> +WLED (White Light Emitting Diode) driver is used for controlling 
>>> display
>>> +backlight that is part of PMIC on Qualcomm Technologies, Inc. 
>>> reference
>>> +platforms. The PMIC is connected to the host processor via SPMI bus.
>>> +
>>> +- compatible
>>> +	Usage:        required
>>> +	Value type:   <string>
>>> +	Definition:   should be "qcom,pm8941-wled" or "qcom,pmi8998-wled".
>>> +		      or "qcom,pm660l-wled".
>> 
>> Better written as
>> 
>> 		should be one of:
>> 		      	X
>> 		      	Y
>> 		      	Z
>> 
> Will do it in the next series.
>>> +
>>> +- reg
>>> +	Usage:        required
>>> +	Value type:   <prop encoded array>
>>> +	Definition:   Base address of the WLED modules.
>>> +
>>> +- interrupts
>>> +	Usage:        optional
>>> +	Value type:   <prop encoded array>
>>> +	Definition:   Interrupts associated with WLED. Interrupts can be
>>> +		      specified as per the encoding listed under
>>> +		      Documentation/devicetree/bindings/spmi/
>>> +		      qcom,spmi-pmic-arb.txt.
>> 
>> Better to describe that this should be the "short" and "ovp" 
>> interrupts
>> in this property than in the interrupt-names.
>> 
> Ok. I will do it in the next series.
>>> +
>>> +- interrupt-names
>>> +	Usage:        optional
>>> +	Value type:   <string>
>>> +	Definition:   Interrupt names associated with the interrupts.
>>> +		      Must be "short" and "ovp". The short circuit detection
>>> +		      is not supported for PM8941.
>>> +
>>> +- label
>>> +	Usage:        required
>>> +	Value type:   <string>
>>> +	Definition:   The name of the backlight device
>>> +
>>> +- default-brightness
>>> +	Usage:        optional
>>> +	Value type:   <u32>
>>> +	Definition:   brightness value on boot, value from: 0-4095
>>> +		      Default: 2048
>>> +
>>> +- qcom,current-limit
>>> +	Usage:        optional
>>> +	Value type:   <u32>
>>> +	Definition:   uA; per-string current limit
>> 
>> You can't change unit on an existing property, that breaks any 
>> existing
>> dts using the qcom,pm8941-wled compatible.
>> 
> 
>>> +		      value:
>>> +		      For pm8941: from 0 to 25000 with 5000 ua step
>>> +				  Default 20000 uA
>>> +		      For pmi8998: from 0 to 30000 with 5000 ua step
>>> +				   Default 25000 uA.
>> 
>> These values could be described just as well in mA, so keep the 
>> original
>> unit - in particular since the boot-limit is in mA...
>> 
> Ok. Will keep the original as is in the next series.
Here, I may have to go with the approach as in "qcom,ovp". Because for 
pm8941
the current step is 1 mA (I have wrongly mentioned as 5000uA here) and 
for PMI8998
the current step is 2.5 mA. Hence, I will add another variable 
"qcom,current-limit-ua"
just like "qcom,ovp-mv".
>>> +
>>> +- qcom,current-boost-limit
>>> +	Usage:        optional
>>> +	Value type:   <u32>
>>> +	Definition:   mA; boost current limit.
>>> +		      For pm8941: one of: 105, 385, 525, 805, 980, 1260, 1400,
>>> +				 1680. Default: 805 mA
>>> +		      For pmi8998: one of: 105, 280, 450, 620, 970, 1150, 1300,
>>> +				  1500. Default: 970 mA
>>> +
>>> +- qcom,switching-freq
>>> +	Usage:        optional
>>> +	Value type:   <u32>
>>> +	Definition:   kHz; switching frequency; one of: 600, 640, 685, 738,
>>> +		      800, 872, 960, 1066, 1200, 1371, 1600, 1920, 2400, 3200,
>>> +		      4800, 9600.
>>> +		      Default: for pm8941: 1600 kHz
>>> +			      for pmi8998: 800 kHz
>>> +
>>> +- qcom,ovp
>>> +	Usage:        optional
>>> +	Value type:   <u32>
>>> +	Definition:   mV; Over-voltage protection limit;
>> 
>> The existing users of qcom,pm8941-wled depends on this being in V, so
>> you can't change the unit. I suggest that you add a new "qcom,ovp-mv"
>> property and make the driver fall back to looking for qcom,ovp if that
>> isn't specified.
>> 
>> PS. This is a very good example of why it is a good idea to not
>> restructure and make changes at the same time - I almost missed this.
>> 
> Actually I have checked the current kernel and none of the properties 
> are
> being configured from the device tree node. Hence, i thought it is the 
> right
> time modify the units to mV to support the PMI8998.
> 
> You still want to have the qcom,ovp-mv, even though it is not being
> configured from
> device tree ?
>>> +		      For pm8941:  one of 27000, 29000, 32000, 35000
>>> +				  Default: 29000 mV
>>> +		      For pmi8998: one of 18100, 19600, 29600, 31100
>>> +				  Default: 29600 mV
>>> +
>>> +- qcom,num-strings
>>> +	Usage:        optional
>>> +	Value type:   <u32>
>>> +	Definition:   #; number of led strings attached;
>>> +		      for pm8941: value 3.
>>> +		      for pmi8998: value 4.
>> 
>> This was the number of strings actually used, so you can't turn this
>> into max number of strings supported. As we have different compatibles
>> for the different pmics this can be hard coded in the driver, based on
>> compatible, and qcom,num-strings can be kept as a special case of
>> qcom,enabled-strings (enabling string 0 through N).
>> 
> Ok. Actually I don't see the use of this property as the 
> qcom,enabled-strings
> it self is enough to know the strings to be enabled. But for backward
> compatibility
> i keep it as original property.
>>> +
>>> +- qcom,enabled-strings
>>> +	Usage:        optional
>>> +	Value tyoe:   <u32>
>>> +	Definition:   Bit mask of the WLED strings. Bit 0 to 3 indicates 
>>> strings
>>> +		      0 to 3 respectively. Each string of leds are operated
>>> +		      individually. Specify the strings using the bit mask. Any
>>> +		      combination of led strings can be used.
>>> +		      for pm8941: Default value is 7 (b111).
>>> +		      for pmi8998: Default value is 15 (b1111).
>> 
>> I think it's better if you describe the enabled strings in an array, 
>> as
>> it makes the dts easier to read and write for humans.
>> 
> ok. I will do that in the next series.
>> Also I'm uncertain about the validity of these defaults, as it's not
>> that the defaults are 7 and 15 it's that if this property is not
>> specified all strings will be enabled and the auto calibration will 
>> kick
>> in to figure out the proper configuration.
>> 
>> It would be better to describe this as "absence of this property will
>> trigger auto calibration".
>> 
> Ok. I will describe it in the next series.
>>> +
>>> +- qcom,cs-out
>>> +	Usage:        optional
>>> +	Value type:   <bool>
>>> +	Definition:   enable current sink output.
>>> +		      This property is supported only for PM8941.
>>> +
>>> +- qcom,cabc
>>> +	Usage:        optional
>>> +	Value type:   <bool>
>>> +	Definition:   enable content adaptive backlight control.
>>> +
>>> +- qcom,ext-gen
>>> +	Usage:        optional
>>> +	Value type:   <bool>
>>> +	Definition:   use externally generated modulator signal to dim.
>>> +		      This property is supported only for PM8941.
>>> +
>>> +- qcom,external-pfet
>>> +	Usage:        optional
>>> +	Value type:   <bool>
>>> +	Definition:   Specify if external PFET control for short circuit
>>> +		      protection is used. This property is supported only
>>> +		      for PMI8998.
>>> +
>>> +- qcom,auto-string-detection
>>> +	Usage:        optional
>>> +	Value type:   <bool>
>>> +	Definition:   Enables auto-detection of the WLED string 
>>> configuration.
>>> +		      This feature is not supported for PM8941.
>> 
>> I don't like the idea of having the developer specifying
>> qcom,enabled-strings and then qcom,auto-string-detection just in case. 
>> I
>> think it's better to trust the developer when qcom,enabled-strings is
>> specified and if not use auto detection.
>> 
> Ok. I will modify the description in that way.
>>> 
>>>  Example:
>>> 
>>> @@ -34,9 +133,26 @@ pm8941-wled@...0 {
>>>  	label = "backlight";
>>> 
>>>  	qcom,cs-out;
>>> -	qcom,current-limit = <20>;
>>> +	qcom,current-limit = <20000>;
>>> +	qcom,current-boost-limit = <805>;
>>> +	qcom,switching-freq = <1600>;
>>> +	qcom,ovp = <29000>;
>>> +	qcom,num-strings = <3>;
>>> +	qcom,enabled-strings = <7>;
>> 
>> Having to change the existing example shows that you made 
>> non-backwards
>> compatible changes.
>> 
> Ok. I will keep them as is in the next series.
>>> +};
>>> +
>>> +pmi8998-wled@...0 {
>>> +	compatible = "qcom,pmi8998-wled";
>>> +	reg = <0xd800 0xd900>;
>>> +	label = "backlight";
>>> +
>>> +	interrupts = <3 0xd8 2 IRQ_TYPE_EDGE_RISING>,
>>> +		     <3 0xd8 1 IRQ_TYPE_EDGE_RISING>;
>>> +	interrupt-names = "short", "ovp";
>>> +	qcom,current-limit = <25000>;
>>>  	qcom,current-boost-limit = <805>;
>>>  	qcom,switching-freq = <1600>;
>>> -	qcom,ovp = <29>;
>>> -	qcom,num-strings = <2>;
>>> +	qcom,ovp = <29600>;
>>> +	qcom,num-strings = <4>;
>>> +	qcom,enabled-strings = <15>;
>>>  };
>>> diff --git a/drivers/video/backlight/qcom-wled.c 
>>> b/drivers/video/backlight/qcom-wled.c
>>> index 0b6d219..be8b8d3 100644
>>> --- a/drivers/video/backlight/qcom-wled.c
>>> +++ b/drivers/video/backlight/qcom-wled.c
>>> @@ -15,253 +15,529 @@
>>>  #include <linux/module.h>
>>>  #include <linux/of.h>
>>>  #include <linux/of_device.h>
>>> +#include <linux/of_address.h>
>>>  #include <linux/regmap.h>
>>> 
>>>  /* From DT binding */
>>> -#define PM8941_WLED_DEFAULT_BRIGHTNESS		2048
>>> +#define WLED_DEFAULT_BRIGHTNESS				2048
>> 
>> These renames are good, but needs to go in a separate commit (either
>> patch 1 or a new one), the current approach makes it impossible to
>> review the rest of this patch.
>> 
>> 
>> So, as the DT change is substantial that should be split in one patch
>> that change the structure, then one that adds the new properties, one
>> patch that renames pm8941 -> wled3 and finally one that adds wled4
>> support.
>> 
> Ok. I will split the patches as you suggested.
>> Regards,
>> Bjorn

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