linux-kernel - Re: [PATCH v3 1/2] leds: mt6360: Add LED driver for MT6360

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Message-ID: <489fc92f-f6f5-839e-e417-7761d404e6ae@gmail.com>
Date:   Thu, 10 Sep 2020 22:23:18 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>,
        Gene Chen <gene.chen.richtek@...il.com>
Cc:     robh+dt@...nel.org, Matthias Brugger <matthias.bgg@...il.com>,
        Dan Murphy <dmurphy@...com>, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Gene Chen <gene_chen@...htek.com>, Wilma.Wu@...iatek.com,
        shufan_lee@...htek.com, cy_huang@...htek.com,
        benjamin.chao@...iatek.com
Subject: Re: [PATCH v3 1/2] leds: mt6360: Add LED driver for MT6360

On 9/10/20 2:29 PM, Pavel Machek wrote:
> Hi!
> 
>>>> +{
>>>> +     struct mt6360_led *led = container_of(lcdev, struct mt6360_led, flash.led_cdev);
>>>> +     struct mt6360_priv *priv = led->priv;
>>>> +     u32 enable_mask = MT6360_TORCHEN_MASK | MT6360_FLCSEN_MASK(led->led_no);
>>>> +     u32 val = (level) ? MT6360_FLCSEN_MASK(led->led_no) : 0;
>>>> +     u32 prev = priv->fled_torch_used, curr;
>>>> +     int ret;
>>>> +
>>>> +     dev_dbg(lcdev->dev, "[%d] brightness %d\n", led->led_no, level);
>>>> +     if (priv->fled_strobe_used) {
>>>> +             dev_warn(lcdev->dev, "Please disable strobe first [%d]\n", priv->fled_strobe_used);
>>>> +             return -EINVAL;
>>>> +     }
>>>
>>> So... how does its userland interface look like?
>>>
>>
>> 1. set FLED1 brightness
>> # echo 1 > /sys/class/leds/white:flash1/flash_brightness
>> 2. enable FLED1 strobe
>> # echo 1 > /sys/class/leds/white:flash1/flash_strobe
>> 3 . turn off FLED1 strobe (just used to gaurantee the strobe mode
>> flash leds must be turned off)
>> # echo 0 > /sys/class/leds/white:flash1/flash_strobe
> 
> I believe I'd preffer only exposing torch functionality in
> /sys/class/leds. .. strobe can be supported using v4l2 APIs.

Actually having LED flash class without strobe is pointless.
If you looked at led_classdev_flash_register_ext() you would see that
it fails with uninitialized strobe_set op. And V4L2 API for strobing
flash calls strobe_set from LED flash class beneath.

That was the idea behind LED and V4L2 flash API unification - there
is one hardware driver needed, the V4L2 Flash layer just takes over
control over it when needed.

-- 
Best regards,
Jacek Anaszewski