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

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Date:   Wed, 12 Feb 2020 23:13:17 +0200
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
Cc:     Helen Koike <helen.koike@...labora.com>,
        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 Dafna,

Apologies for the late reply. I learned the mail had got lost due to mail
server issues.

On Fri, Jan 31, 2020 at 08:38:34PM +0100, Dafna Hirschfeld wrote:
> 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' ?

Yes.

> 
> > > 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.

It needs to be set before the video device is registered, so indeed, it
seems no driver can make use it.

> 
> > 
> > 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?

Please do. That's what other drivers do at the moment as well.

-- 
Kind regards,

Sakari Ailus