linux-kernel - Re: [PATCH v9 2/2] Add support for OV5647 sensor.

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Message-ID: <21847f33-901c-7d26-15d8-6b92f10c8b15@mentor.com>
Date:   Tue, 21 Feb 2017 22:36:13 +0200
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Ramiro Oliveira <Ramiro.Oliveira@...opsys.com>,
        <linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <devicetree@...r.kernel.org>
CC:     <CARLOS.PALMINHA@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pali Rohár <pali.rohar@...il.com>,
        Pavel Machek <pavel@....cz>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Rob Herring <robh+dt@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Steve Longerbeam <slongerbeam@...il.com>
Subject: Re: [PATCH v9 2/2] Add support for OV5647 sensor.

Hi Ramiro,

On 02/21/2017 06:42 PM, Ramiro Oliveira wrote:
> Hi Vladimir,
> 
> Thank you for your feedback
> 
> On 2/21/2017 3:54 PM, Vladimir Zapolskiy wrote:
>> Hi Ramiro,
>>
>> please find some review comments below.
>>
>> On 02/17/2017 03:14 PM, Ramiro Oliveira wrote:
>>> The OV5647 sensor from Omnivision supports up to 2592x1944 @ 15 fps, RAW 8
>>> and RAW 10 output formats, and MIPI CSI-2 interface.
>>>
>>> The driver adds support for 640x480 RAW 8.
>>>
>>> Signed-off-by: Ramiro Oliveira <roliveir@...opsys.com>
>>> ---
>>
>> [snip]
>>
>>> +
>>> +struct ov5647 {
>>> +	struct v4l2_subdev		sd;
>>> +	struct media_pad		pad;
>>> +	struct mutex			lock;
>>> +	struct v4l2_mbus_framefmt	format;
>>> +	unsigned int			width;
>>> +	unsigned int			height;
>>> +	int				power_count;
>>> +	struct clk			*xclk;
>>> +	/* External clock frequency currently supported is 30MHz */
>>> +	u32				xclk_freq;
>>
>> See a comment about 25MHz vs 30MHz below.
>>
>> Also I assume you can remove 'xclk_freq' from the struct fields,
>> it can be replaced by a local variable.
>>
> 
> I'll do that.
> 
>>> +};
>>
>> [snip]
>>
>>> +
>>> +static int ov5647_read(struct v4l2_subdev *sd, u16 reg, u8 *val)
>>> +{
>>> +	int ret;
>>> +	unsigned char data_w[2] = { reg >> 8, reg & 0xff };
>>> +	struct i2c_client *client = v4l2_get_subdevdata(sd);
>>> +
>>> +	ret = i2c_master_send(client, data_w, 2);
>>> +	if (ret < 0) {
>>> +		dev_dbg(&client->dev, "%s: i2c read error, reg: %x\n",
>>
>> s/i2c read error/i2c write error/
>>
> 
> I'm not sure I understand what you mean.

That's a sed expression for string substitution. Here you do i2c_master_send()
but dev_dbg() comment says "i2c read error". It's a simple copy-paste typo to fix.

>>> +			__func__, reg);
>>> +		return ret;
>>> +	}
>>> +

[snip]

>>> +
>>> +static int sensor_power(struct v4l2_subdev *sd, int on)

On the caller's side (functions ov5647_open() and ov5647_close()) the second
argument of the function is of 'bool' type, however .s_power callback from
struct v4l2_subdev_core_ops (see include/media/v4l2-subdev.h) defines it as
'int'.

It's just a nitpicking, please feel free to ignore the comment above or
please consider to change the arguments on callers' side to integers.

Also you may consider to add 'ov5647_' prefix to the function name to
distinguish it from a potentially added in future sensor_power() function,
the original name sounds too generic.

>>> +{
>>> +	int ret;
>>> +	struct ov5647 *ov5647 = to_state(sd);
>>> +	struct i2c_client *client = v4l2_get_subdevdata(sd);
>>> +
>>> +	ret = 0;
>>> +	mutex_lock(&ov5647->lock);
>>> +
>>> +	if (on && !ov5647->power_count)	{
>>> +		dev_dbg(&client->dev, "OV5647 power on\n");
>>> +
>>> +		clk_set_rate(ov5647->xclk, ov5647->xclk_freq);
>>
>> Now clk_set_rate() is redundant, please remove it.
>>
>> If once it is needed again, please move it to the .probe function, so
>> it is called only once in the runtime.
>>
> 
> Ok. I'll remove it for now.
> 
>>> +
>>> +		ret = clk_prepare_enable(ov5647->xclk);
>>
>> I wonder would it be possible to unload the driver or to unbind the device
>> and leave the clock unintentionally enabled? If yes, then this is a bug.
>>
> 
> You're saying that if the driver was unloaded and the clock was left enabled
> when the driver was loaded again this line would cause an error?

Not exactly, here I saw a potential resource leak, namely a potentially left
prepared/enabled clock.

> 
> Should I disable the clock when the driver is removed?
> 

The driver (and framework) shall guarantee that when it is detached from
device(s) (e.g. by unloading "ov5647" kernel module or unbinding ov5647 device),
all acquired resources are released.

But in this particular case most probably I've been overly alert, I believe
that V4L2 framework correcly handles device power states, so please ignore my
comment.

To add something valuable to the review, could you please confirm that
ov5647_subdev_internal_ops data is in use by the driver?

E.g. shouldn't it be registered by

  sd->internal_ops = &ov5647_subdev_internal_ops;

before calling v4l2_async_register_subdev(sd) ?

--
With best wishes,
Vladimir