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

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Message-ID: <7e67c8f7-7f79-72f8-05bc-022ed0655a3f@gmail.com>
Date:   Fri, 11 Sep 2020 23:21:32 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Gene Chen <gene.chen.richtek@...il.com>,
        Pavel Machek <pavel@....cz>
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 9/11/20 1:24 AM, Gene Chen wrote:
> Pavel Machek <pavel@....cz> 於 2020年9月11日 週五 下午3:05寫道：
>>
>> 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);
>>>
>>> Doesn't hardware handle that? IOW, what happens when you have enabled
>>> both torch and flash? If flash just overrides torch mode, than you
>>> should not prevent enabling torch in this case.
>>
>> Yep, this is strange/confusing... and was reason why I asked for not
>> supporting strobe from sysfs.
>>
>> Could I get you to remove code you are not commenting at when
>> reviewing?
>>
> 
> MT6360 FLED register define is STROBE_EN/TORCH_EN/CS1/CS2 (current
> source) 4 bits.
> The STROBE_EN/TORCH_EN is shared by FLED1 and FLED2.
> If I want to enable FLED1 torch mode, I set TORCH_EN and CS1
> If I want to enable FLED2 strobe mode, I set STROBE_EN and CS2
> For example I set FLED1 torch, then I set FLED2 strobe.
> When I set FLED2 strobe, I will see the strobe current is FLED2 add
> FLED1 current which is not I want.
> So I need disable FLED1 torch first.
> Considering every circumstances is complicated when share same H/W
> logic control.
> And the other problem is torch mode switch to strobe mode needs ramp
> time because strobe and torch mode can't be co-exist.

Thank you for the explanation. So we have to keep your guards
but I would return -EBUSY instead of -EINVAL.

This would be also consistent with what
drivers/media/v4l2-core/v4l2-flash-led-class.c
does in its v4l2_flash_s_ctrl(), case V4L2_CID_FLASH_STROBE - it returns
-EBUSY if __software_strobe_mode_inactive() returns false.

The advantage of V4L2 Flash interface is that it has LED_MODE that
can be set to torch or flash, but in LED subsystem we don't have
the counterpart.

-- 
Best regards,
Jacek Anaszewski