linux-kernel - Re: [PATCH v3 1/5] leds: lm3532: Fix brightness control for i2c mode

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Date:   Wed, 28 Aug 2019 10:28:01 -0500
From:   Dan Murphy <dmurphy@...com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>, Tony Lindgren <tony@...mide.com>
CC:     <sre@...nel.org>, <nekit1000@...il.com>, <mpartap@....net>,
        <merlijn@...zup.org>, <linux-leds@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/5] leds: lm3532: Fix brightness control for i2c mode

Jacek

On 8/27/19 4:14 PM, Jacek Anaszewski wrote:
> Dan,
>
> On 8/27/19 2:44 PM, Dan Murphy wrote:
>> Tony
>>
>> On 8/27/19 7:18 AM, Pavel Machek wrote:
>>> On Mon 2019-08-26 15:44:37, Tony Lindgren wrote:
>>>> * Pavel Machek <pavel@....cz> [190826 22:14]:
>>>>> On Mon 2019-08-26 14:58:22, Tony Lindgren wrote:
>>>>>> Hi,
>>>>>>
>>>>>> * Dan Murphy <dmurphy@...com> [190820 19:53]:
>>>>>>> Fix the brightness control for I2C mode.  Instead of
>>>>>>> changing the full scale current register update the ALS target
>>>>>>> register for the appropriate banks.
>>>>>>>
>>>>>>> In addition clean up some code errors and random misspellings found
>>>>>>> during coding.
>>>>>>>
>>>>>>> Tested on Droid4 as well as LM3532 EVM connected to a BeagleBoneBlack
>>>>>>>
>>>>>>> Fixes: e37a7f8d77e1 ("leds: lm3532: Introduce the lm3532 LED driver")
>>>>>>> Reported-by: Pavel Machek <pavel@....cz>
>>>>>>> Signed-off-by: Dan Murphy <dmurphy@...com>
>>>>>>> ---
>>>>>>>
>>>>>>> v3 - Removed register define updates -
>>>>>>> https://lore.kernel.org/patchwork/patch/1114542/
>>>>>> Looks like starting with this patch in Linux next the LCD on droid4
>>>>>> is so dim it's unreadable even with brightness set to 255. Setting
>>>>>> brightness to 0 does blank it completely though.
>>>>>>
>>>>>> Did something maybe break with the various patch revisions or are
>>>>>> we now missing some dts patch?
>>>>> Maybe missing dts patch. We should provide maximum current the LED can
>>>>> handle...
>>>> Or i2c control is somehow broken and only als control now works?
>> With only setting CONFIG_LEDS_LM3532=m to the next branch I get full
>> brightness with 255.
>>
>> I also see half brightness at 128 with the ramp down working.
>>
>> I am not able to reproduce this issue on my device.
>>
>>> Well, max current led is obviously missing. Plus code does not check
>>> the return from reading led-max-microamp.
>> led-max-microamp is optional so there is no need to check the return.
> It's also ugly to not check it when you have it assigned.
> We'll soon receive complaints from static checkers about pointless
> assignment.
>
> I'd distinguish between cases when parsing failed,
> and when property has not been provided.
>
> if (fwnode_property_present(child, "led-max-microamp")) {
> 	if (fwnode_property_read_u32(child, "led-max-microamp",
> 				&led->full_scale_current);
> 		dev_err(&priv->client->dev,
>                           "Failed to parse led-max-microamp property\n")

I am OK with doing this but I think the else case logging is extra.

Again the property is optional and if the user decides not to populate 
it then there should not

be a log of that it is missing.

Dan

> } else {
> 	dev_info(&priv->client->dev,
> 		 led-max-microamp property is missing\n")
> }
>
>> full_scale_current should be 0 if not populated and in the init only if
>> this variable is set does
>>
>> the code program the register otherwise it is default of 20.2 mA.