linux-kernel - Re: [PATCH v8 05/14] media: rkisp1: add Rockchip ISP1 subdev driver

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Date:   Fri, 31 Jan 2020 20:38:34 +0100
From:   Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Helen Koike <helen.koike@...labora.com>
Cc:     linux-rockchip@...ts.infradead.org, devicetree@...r.kernel.org,
        eddie.cai.linux@...il.com, mchehab@...nel.org, heiko@...ech.de,
        jacob2.chen@...k-chips.com, jeffy.chen@...k-chips.com,
        zyc@...k-chips.com, linux-kernel@...r.kernel.org,
        tfiga@...omium.org, hans.verkuil@...co.com,
        laurent.pinchart@...asonboard.com, kernel@...labora.com,
        ezequiel@...labora.com, linux-media@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, zhengsq@...k-chips.com,
        Jacob Chen <cc@...k-chips.com>,
        Allon Huang <allon.huang@...k-chips.com>,
        Dafna Hirschfeld <dafna3@...il.com>
Subject: Re: [PATCH v8 05/14] media: rkisp1: add Rockchip ISP1 subdev driver

Hi,
I (Dafna Hirschfeld) will work in following months with Helen Koike to fix the issues
in the TODO file of this driver: drivers/staging/media/rkisp1/TODO

On 15.08.19 15:17, Sakari Ailus wrote:
> On Thu, Aug 15, 2019 at 11:24:22AM +0300, Sakari Ailus wrote:
>> Hi Helen,
>>
>> On Wed, Aug 14, 2019 at 09:58:05PM -0300, Helen Koike wrote:
>>
>> ...
>>
>>>>> +static int rkisp1_isp_sd_set_fmt(struct v4l2_subdev *sd,
>>>>> +				 struct v4l2_subdev_pad_config *cfg,
>>>>> +				 struct v4l2_subdev_format *fmt)
>>>>> +{
>>>>> +	struct rkisp1_device *isp_dev = sd_to_isp_dev(sd);
>>>>> +	struct rkisp1_isp_subdev *isp_sd = &isp_dev->isp_sdev;
>>>>> +	struct v4l2_mbus_framefmt *mf = &fmt->format;
>>>>> +
>>>>
>>>> Note that for sub-device nodes, the driver is itself responsible for
>>>> serialising the access to its data structures.
>>>
>>> But looking at subdev_do_ioctl_lock(), it seems that it serializes the
>>> ioctl calls for subdevs, no? Or I'm misunderstanding something (which is
>>> most probably) ?
>>
>> Good question. I had missed this change --- subdev_do_ioctl_lock() is
>> relatively new. But setting that lock is still not possible as the struct

'the struct' - do you mean the 'vdev' struct allocated in
'v4l2_device_register_subdev_nodes' ?

>> is allocated in the framework and the device is registered before the

>> driver gets hold of it. It's a good idea to provide the same serialisation
>> for subdevs as well.
>>
>> I'll get back to this later.
> 
> The main reason is actually that these ops are also called through the
> sub-device kAPI, not only through the uAPI, and the locks are only taken
> through the calls via uAPI.

actually it seems that although 'subdev_do_ioctl_lock' exit, I wonder if
any subdevice uses that vdev->lock in  subdev_do_ioctl_lock.
It is not initialized in v4l2_device_register_subdev_nodes where the vdev is allocated
and I wonder if any subdevice actually initialize it somewhere else. For example it is null in this
driver and in vimc.

> 
> So adding the locks to uAPI calls alone would not address the issue.

What I can do is add a mutex to every struct of a subdevice and lock it
at the beginning of each subdevice operation.
Is this an acceptable solution?

Thanks,
Dafna
>