linux-kernel - Re: [PATCH v5 3/6] media: platform: visconti: Add Toshiba Visconti Video Input Interface driver user interace

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Message-ID: <Y8dFlFkVJS/6+Ib1@pendragon.ideasonboard.com>
Date:   Wed, 18 Jan 2023 03:04:20 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Mark Brown <broonie@...nel.org>, linux-media@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v5 3/6] media: platform: visconti: Add Toshiba Visconti
 Video Input Interface driver user interace

Hello,

On Tue, Jan 17, 2023 at 12:47:10PM +0100, Hans Verkuil wrote:
> More comments below:
> 
> On 11/01/2023 03:24, Yuji Ishikawa wrote:
> > Add support to Video Input Interface on Toshiba Visconti ARM SoCs.
> > The interface device includes CSI2 Receiver,
> > frame grabber, video DMAC and image signal processor.
> > This patch provides the user interface layer.
> > 
> > A driver instance provides three /dev/videoX device files;
> > one for RGB image capture, another one for optional RGB capture
> > with different parameters and the last one for RAW capture.
> > 
> > Through the device files, the driver provides streaming (DMA-BUF) interface.
> > A userland application should feed DMA-BUF instances for capture buffers.
> > 
> > The driver is based on media controller framework.
> > Its operations are roughly mapped to two subdrivers;
> > one for ISP and CSI2 receiver (yields 1 instance),
> > the other for capture (yields 3 instances for each capture mode).
> > 
> > Signed-off-by: Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>
> > ---
> > Changelog v2:
> > - Resend v1 because a patch exceeds size limit.
> > 
> > Changelog v3:
> > - Adapted to media control framework
> > - Introduced ISP subdevice, capture device
> > - Remove private IOCTLs and add vendor specific V4L2 controls
> > - Change function name avoiding camelcase and uppercase letters
> > 
> > Changelog v4:
> > - Split patches because the v3 patch exceeds size limit 
> > - Stop using ID number to identify driver instance:
> >   - Use dynamically allocated structure to hold HW specific context,
> >     instead of static one.
> >   - Call HW layer functions with the context structure instead of ID number
> > - Use pm_runtime to trigger initialization of HW
> >   along with open/close of device files.
> > 
> > Changelog v5:
> > - Fix coding style problems in viif.c
> > ---
> >  drivers/media/platform/visconti/Makefile      |    1 +
> >  drivers/media/platform/visconti/viif.c        |  545 ++++++++
> >  drivers/media/platform/visconti/viif.h        |  203 +++
> >  .../media/platform/visconti/viif_capture.c    | 1201 +++++++++++++++++
> >  drivers/media/platform/visconti/viif_isp.c    |  846 ++++++++++++
> >  5 files changed, 2796 insertions(+)
> >  create mode 100644 drivers/media/platform/visconti/viif.c
> >  create mode 100644 drivers/media/platform/visconti/viif.h
> >  create mode 100644 drivers/media/platform/visconti/viif_capture.c
> >  create mode 100644 drivers/media/platform/visconti/viif_isp.c

[snip]

> > +static int viif_s_edid(struct file *file, void *fh, struct v4l2_edid *edid)
> > +{
> > +	struct viif_device *viif_dev = video_drvdata_to_capdev(file)->viif_dev;
> > +	struct viif_subdev *viif_sd = viif_dev->sd;
> > +
> > +	return v4l2_subdev_call(viif_sd->v4l2_sd, pad, set_edid, edid);
> > +}
> 
> Has this driver been tested with an HDMI receiver? If not, then I would recommend
> dropping support for it until you actually can test with such hardware.
> 
> The DV_TIMINGS API is for HDMI/DVI/DisplayPort etc. interfaces, it's not meant
> for CSI and similar interfaces.

More than that, for MC-based drivers, the video node should *never*
forward ioctls to a connected subdev. The *only* valid calls to
v4l2_subdev_call() in this file are

- to video.s_stream() in the start and stop streaming handler

- to pad.g_fmt() when starting streaming to validate that the connected
  subdev outputs a format compatible with the format set on the video
  capture device

That's it, nothing else, all other calls to v4l2_subdev_call() must be
dropped from the implementation of the video_device.

[snip]

-- 
Regards,

Laurent Pinchart