linux-kernel - Re: [PATCH 3/3] backlight: lp855x: Add support ACPI enumeration

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Message-ID: <20211102122253.s4oc2p7hmy7w2qgn@maple.lan>
Date:   Tue, 2 Nov 2021 12:22:53 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] backlight: lp855x: Add support ACPI enumeration

On Mon, Nov 01, 2021 at 07:55:17PM +0100, Hans de Goede wrote:
> The Xiaomi Mi Pad 2 tablet uses an ACPI enumerated LP8556 backlight
> controller for its LCD-panel, with a Xiaomi specific ACPI HID of
> "XMCC0001", add support for this.
> 
> Note the new "if (id)" check also fixes a NULL pointer deref when a user
> tries to manually bind the driver from sysfs.
> 
> When CONFIG_ACPI is disabled acpi_match_device() will always return NULL,
> so the lp855x_parse_acpi() call will get optimized away.
> 
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
>  drivers/video/backlight/lp855x_bl.c | 70 ++++++++++++++++++++++++-----
>  1 file changed, 60 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/video/backlight/lp855x_bl.c b/drivers/video/backlight/lp855x_bl.c
> index d1d27d5eb0f2..f075ec84acfb 100644
> --- a/drivers/video/backlight/lp855x_bl.c
> +++ b/drivers/video/backlight/lp855x_bl.c
> @@ -338,10 +339,6 @@ static int lp855x_parse_dt(struct lp855x *lp)
>  		return -EINVAL;
>  	}
>  
> -	pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
> -	if (!pdata)
> -		return -ENOMEM;
> -
>  	of_property_read_string(node, "bl-name", &pdata->name);
>  	of_property_read_u8(node, "dev-ctrl", &pdata->device_control);
>  	of_property_read_u8(node, "init-brt", &pdata->initial_brightness);

Shouldn't there be a removal of an `lp->pdata = pdata` from somewhere in
this function?


> @@ -379,8 +376,31 @@ static int lp855x_parse_dt(struct lp855x *lp)
>  }
>  #endif
>  
> +static int lp855x_parse_acpi(struct lp855x *lp)
> +{
> +	int ret;
> +
> +	/*
> +	 * On ACPI the device has already been initialized by the firmware

Perhaps nitpicking but ideally I'd like "and is in register mode" here 
since I presume it can also be assumed that everything with this HID
has adopted that).

Other than these, LGTM.


Daniel.