linux-kernel - Re: [PATCH v1 1/2] leds: rt4505: Add support for Richtek RT4505 flash led controller

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Message-ID: <CADiBU3_x=9wvPv4_YxWx4H_ecV7Kbt5ur91SDv+unH4z2hzS_Q@mail.gmail.com>
Date:   Wed, 28 Oct 2020 12:57:42 +0800
From:   ChiYuan Huang <u0084500@...il.com>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Pavel Machek <pavel@....cz>, dmurphy@...com, robh+dt@...nel.org,
        linux-leds@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        cy_huang <cy_huang@...htek.com>, devicetree@...r.kernel.org
Subject: Re: [PATCH v1 1/2] leds: rt4505: Add support for Richtek RT4505 flash
 led controller

Hi,

Jacek Anaszewski <jacek.anaszewski@...il.com> 於 2020年10月28日 週三 上午12:40寫道：
>
> Hi Pavel, ChiYuan,
>
> On 10/27/20 9:29 AM, Pavel Machek wrote:
> > Hi!
> >
> >> From: ChiYuan Huang <cy_huang@...htek.com>
> >>
> >> Add support for RT4505 flash led controller. It can support up to 1.5A
> >> flash current with hardware timeout and low input voltage
> >> protection.
> >
> > Please use upper-case "LED" everywhere.
> >
> > This should be 2nd in the series, after DT changes.
> >
> >> Signed-off-by: ChiYuan Huang <cy_huang@...htek.com>
> >> ---
> >>   drivers/leds/Kconfig       |  11 ++
> >>   drivers/leds/Makefile      |   1 +
> >>   drivers/leds/leds-rt4505.c | 397 +++++++++++++++++++++++++++++++++++++++++++++
> >>   3 files changed, 409 insertions(+)
> >>   create mode 100644 drivers/leds/leds-rt4505.c
> [...]
> >> +static int rt4505_torch_brightness_set(struct led_classdev *lcdev, enum led_brightness level)
> >> +{
> >
> > 80 columns, where easy.
> >
> >> +    struct rt4505_priv *priv = container_of(lcdev, struct rt4505_priv, flash.led_cdev);
> >> +    u32 val = 0;
> >> +    int ret;
> >> +
> >> +    mutex_lock(&priv->lock);
> >> +
> >> +    if (level != LED_OFF) {
> >> +            ret = regmap_update_bits(priv->regmap, RT4505_REG_ILED, RT4505_ITORCH_MASK,
> >> +                                     (level - 1) << RT4505_ITORCH_SHIFT);
> >> +            if (ret)
> >> +                    goto unlock;
> >> +
> >> +            val = RT4505_TORCH_SET;
> >> +    }
> >> +
> >> +    ret = regmap_update_bits(priv->regmap, RT4505_REG_ENABLE, RT4505_ENABLE_MASK, val);
> >> +
> >> +unlock:
> >> +    mutex_unlock(&priv->lock);
> >> +    return ret;
> >> +}
> >
> > Why is the locking needed? What will the /sys/class/leds interface
> > look like on system with your flash?
>
> The locking is needed since this can be called via led_set_brightness()
> from any place in the kernel, and especially from triggers.
>From this case, It means only led classdev
brihtness_get/brightness_set need to be protected.
I search led_flash_classdev, it only can be controlled via sysfs or V4l2.
Like as described in last mail, flash related operation is protected
by led access_lock and v4l2 framework.
I'll keep the locking only in led classdev brightness_get/brightness_set API.
If I misunderstand something, please help to point out.
Thx.
>
> --
> Best regards,
> Jacek Anaszewski