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

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Message-ID: <CADiBU3-y4PMtedP7fe22LW_x6bnsbyUYUHb+tNTZctJ=1wTYbA@mail.gmail.com>
Date:   Wed, 28 Oct 2020 19:14:35 +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

Jacek Anaszewski <jacek.anaszewski@...il.com> 於 2020年10月28日 週三 下午7:07寫道：
>
> On 10/28/20 5:57 AM, ChiYuan Huang wrote:
> > 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.
>
> Locking have to be used consistently for each access to the resource
> being protected with the lock. Otherwise you can end up in a situation
> when rt4505_torch_brightness_set and rt4505_flash_brightness_set will
> try concurrently alter hardware state. Regardless of how harmful could
> it be in case of this particular device it is certainly against
> programming rules.
>
Sure, any resource access must be protected.
I'll keep the locking like as the original patch.
Thx.
> --
> Best regards,
> Jacek Anaszewski