| Message ID | 20170825083531.6e5e2c84@vento.lan (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 25/08/17 13:35, Mauro Carvalho Chehab wrote: > Em Fri, 25 Aug 2017 08:30:37 -0300 > Mauro Carvalho Chehab <mchehab@osg.samsung.com> escreveu: > >> Em Fri, 25 Aug 2017 08:15:03 -0300 >> Mauro Carvalho Chehab <mchehab@s-opensource.com> escreveu: >> >>> Em Fri, 25 Aug 2017 12:56:30 +0200 >>> Hans Verkuil <hverkuil@xs4all.nl> escreveu: >>> >>>> On 25/08/17 12:50, Mauro Carvalho Chehab wrote: >>>>> Em Fri, 25 Aug 2017 12:42:51 +0200 >>>>> Hans Verkuil <hansverk@cisco.com> escreveu: >>>>> >>>>>> On 08/25/2017 12:35 PM, Mauro Carvalho Chehab wrote: >>>>>>> Em Fri, 25 Aug 2017 12:13:53 +0200 >>>>>>> Hans Verkuil <hansverk@cisco.com> escreveu: >>>>>>> >>>>>>>> On 08/25/2017 12:06 PM, Mauro Carvalho Chehab wrote: >>>>>>>>> Em Fri, 25 Aug 2017 11:44:27 +0200 >>>>>>>>> Hans Verkuil <hansverk@cisco.com> escreveu: >>>>>>>>> >>>>>>>>>> On 08/25/2017 11:40 AM, Mauro Carvalho Chehab wrote: >>>>>>>>>>> From: Mauro Carvalho Chehab <mchehab@osg.samsung.com> >>>>>>>>>>> >>>>>>>>>>> As both vdev-centric and mc-centric devices may implement the >>>>>>>>>>> same APIs, we need a flag to allow userspace to distinguish >>>>>>>>>>> between them. >>>>>>>>>>> >>>>>>>>>>> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com> >>>>>>>>>>> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> >>>>>>>>>>> --- >>>>>>>>>>> Documentation/media/uapi/v4l/open.rst | 6 ++++++ >>>>>>>>>>> Documentation/media/uapi/v4l/vidioc-querycap.rst | 4 ++++ >>>>>>>>>>> include/uapi/linux/videodev2.h | 2 ++ >>>>>>>>>>> 3 files changed, 12 insertions(+) >>>>>>>>>>> >>>>>>>>>>> diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst >>>>>>>>>>> index a72d142897c0..eb3f0ec57edb 100644 >>>>>>>>>>> --- a/Documentation/media/uapi/v4l/open.rst >>>>>>>>>>> +++ b/Documentation/media/uapi/v4l/open.rst >>>>>>>>>>> @@ -33,6 +33,12 @@ For **vdev-centric** control, the device and their corresponding hardware >>>>>>>>>>> pipelines are controlled via the **V4L2 device** node. They may optionally >>>>>>>>>>> expose via the :ref:`media controller API <media_controller>`. >>>>>>>>>>> >>>>>>>>>>> +.. note:: >>>>>>>>>>> + >>>>>>>>>>> + **vdev-centric** devices should report V4L2_VDEV_CENTERED >>>>>>>>>> >>>>>>>>>> You mean CENTRIC, not CENTERED. >>>>>>>>> >>>>>>>>> Yeah, true. I'll fix it. >>>>>>>>> >>>>>>>>>> But I would change this to MC_CENTRIC: the vast majority of drivers are VDEV centric, >>>>>>>>>> so it makes a lot more sense to keep that as the default and only set the cap for >>>>>>>>>> MC-centric drivers. >>>>>>>>> >>>>>>>>> I actually focused it on what an userspace application would do. >>>>>>>>> >>>>>>>>> An specialized application for a given hardware will likely just >>>>>>>>> ignore whatever flag is added, and use vdev, mc and subdev APIs >>>>>>>>> as it pleases. So, those applications don't need any flag at all. >>>>>>>>> >>>>>>>>> However, a generic application needs a flag to allow them to check >>>>>>>>> if a given hardware can be controlled by the traditional way >>>>>>>>> to control the device (e. g. if it accepts vdev-centric type of >>>>>>>>> hardware control). >>>>>>>>> >>>>>>>>> It is an old desire (since when MC was designed) to allow that >>>>>>>>> generic V4L2 apps to also work with MC-centric hardware somehow. >>>>>>>> >>>>>>>> No, not true. The desire is that they can use the MC to find the >>>>>>>> various device nodes (video, radio, vbi, rc, cec, ...). But they >>>>>>>> remain vdev-centric. vdev vs mc centric has nothing to do with the >>>>>>>> presence of the MC. It's how they are controlled. >>>>>>> >>>>>>> No, that's not I'm talking about. I'm talking about libv4l plugin >>>>>>> (or whatever) that would allow a generic app to work with a mc-centric >>>>>>> device. That's there for a long time (since when we were reviewing >>>>>>> the MC patches back in 2009 or 2010). >>>>>> >>>>>> So? Such a plugin would obviously remove the MC_CENTRIC cap. Which makes >>>>>> perfect sense. >>>>>> >>>>>> There are a lot of userspace applications that do not use libv4l. It's >>>>>> optional, not required, to use that library. We cannot design our API with >>>>>> the assumption that this library will be used. >>>>>> >>>>>>> >>>>>>>> >>>>>>>> Regarding userspace applications: they can't check for a VDEV_CENTRIC >>>>>>>> cap since we never had any. I.e., if they do: >>>>>>>> >>>>>>>> if (!(caps & VDEV_CENTRIC)) >>>>>>>> /* unsupported device */ >>>>>>>> >>>>>>>> then they would fail for older kernels that do not set this flag. >>>>>>>> >>>>>>>> But this works: >>>>>>>> >>>>>>>> if (caps & MC_CENTRIC) >>>>>>>> /* unsupported device */ >>>>>>>> >>>>>>>> So this really needs to be an MC_CENTRIC capability. >>>>>>> >>>>>>> That won't work. The test should take into account the API version >>>>>>> too. >>>>>>> >>>>>>> Assuming that such flag would be added for version 4.15, with a VDEV_CENTRIC, >>>>>>> the check would be: >>>>>>> >>>>>>> >>>>>>> /* >>>>>>> * There's no need to check version here: libv4l may override it >>>>>>> * to support a mc-centric device even for older versions of the >>>>>>> * Kernel >>>>>>> */ >>>>>>> if (caps & V4L2_CAP_VDEV_CENTRIC) >>>>>>> is_supported = true; >>>>>>> >>>>>>> /* >>>>>>> * For API version lower than 4.15, there's no way to know for >>>>>>> * sure if the device is vdev-centric or not. So, either additional >>>>>>> * tests are needed, or it would assume vdev-centric and output >>>>>>> * some note about that. >>>>>>> */ >>>>>>> if (version < KERNEL_VERSION(4, 15, 0)) >>>>>>> maybe_supported = true; >>>>>> >>>>>> >>>>>> is_supported = true; >>>>>> if (caps & V4L2_CAP_MC_CENTRIC) >>>>>> is_supported = false; >>>>>> if (version < KERNEL_VERSION(4, 15, 0)) >>>>>> maybe_supported = true; >>>>>> >>>>>> I don't see the difference. BTW, no application will ever do that version check. >>>>>> It doesn't help them in any way to know that it 'may' be supported. >>>>> >>>>> Yeah, this can work. The only drawback is that, if we end by >>>>> implementing vdev compatible support is that such drivers will >>>>> have to clean the V4L2_CAP_MC_CENTRIC flag. >>>> >>>> You mean implementing vdev compatible support in libv4l? (Just making sure >>>> I understand you correctly) >>> >>> Yes, either there or at the Kernel, as it seems we'll never have it >>> there, as nobody is working on it anymore. >>> >>>> In that case it doesn't matter if the libv4l code would set the VDEV_CENTRIC flag >>>> or remove the MC_CENTRIC flag. That makes no difference, or course. >>> >>> True, but the text will have to be clear that a MC_CENTRIC device is a >>> device that can't be controlled by a V4L2-centric application. >> >> Ok, that's the "reverse" patch. IMHO, it is very confusing, as we're >> actually using MC_CENTRIC to actually describe the lack of a capability. >> >> Perhaps we should name it as NOT_VDEV_CENTRIC instead. > > Hans suggested an alternative word at the IRC ("require"), with actually > sounds better. Patch follows. > > I can live it that :-) > > Regards, > Mauro > > - > > media: videodev2: add a flag for vdev-centric devices > > As both vdev-centric and mc-centric devices may implement the > same APIs, we need a flag to allow userspace to distinguish > between them. > > Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com> > > diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst > index a72d142897c0..4b344dccd2ac 100644 > --- a/Documentation/media/uapi/v4l/open.rst > +++ b/Documentation/media/uapi/v4l/open.rst > @@ -6,6 +6,8 @@ > Opening and Closing Devices > *************************** > > +.. _v4l2_hardware_control: > + > Types of V4L2 hardware control > ============================== > > @@ -33,6 +35,13 @@ For **vdev-centric** control, the device and their corresponding hardware > pipelines are controlled via the **V4L2 device** node. They may optionally > expose via the :ref:`media controller API <media_controller>`. > > +.. note:: > + > + Devices that require **mc-centric** hardware control should report s/should/shall/ Shouldn't we use MC-centric? (i.e. capital MC) I think that's better. > + a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag s/a/the/ > + (see :ref:`VIDIOC_QUERYCAP`). > + > + > For **MC-centric** control, before using the V4L2 device, it is required to > set the hardware pipelines via the > :ref:`media controller API <media_controller>`. For those devices, the > diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst > index 12e0d9a63cd8..2b08723375bc 100644 > --- a/Documentation/media/uapi/v4l/vidioc-querycap.rst > +++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst > @@ -252,6 +252,11 @@ specification the ioctl returns an ``EINVAL`` error code. > * - ``V4L2_CAP_TOUCH`` > - 0x10000000 > - This is a touch device. > + * - ``V4L2_MC_CENTRIC`` > + - 0x20000000 > + - Indicates that the device require **mc-centric** hardware requires > + control, and thus can't be used by **v4l2-centric** applications. So are we using V4L2-centric or vdev-centric? It seems to be mixed now. And if we use V4L2-centric then it should be capitals as well. > + See :ref:`v4l2_hardware_control` for more details. > * - ``V4L2_CAP_DEVICE_CAPS`` > - 0x80000000 > - The driver fills the ``device_caps`` field. This capability can > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h > index 45cf7359822c..7b490fe97980 100644 > --- a/include/uapi/linux/videodev2.h > +++ b/include/uapi/linux/videodev2.h > @@ -460,6 +460,8 @@ struct v4l2_capability { > > #define V4L2_CAP_TOUCH 0x10000000 /* Is a touch device */ > > +#define V4L2_CAP_MC_CENTRIC 0x20000000 /* Device require mc-centric hardware control */ requires > + > #define V4L2_CAP_DEVICE_CAPS 0x80000000 /* sets device capabilities field */ > > /* > This is getting close. Can you post the whole patch series for the next revision? It's a bit hard to review with patches in replies. Regards, Hans
diff --git a/Documentation/media/uapi/v4l/open.rst b/Documentation/media/uapi/v4l/open.rst index a72d142897c0..4b344dccd2ac 100644 --- a/Documentation/media/uapi/v4l/open.rst +++ b/Documentation/media/uapi/v4l/open.rst @@ -6,6 +6,8 @@ Opening and Closing Devices *************************** +.. _v4l2_hardware_control: + Types of V4L2 hardware control ============================== @@ -33,6 +35,13 @@ For **vdev-centric** control, the device and their corresponding hardware pipelines are controlled via the **V4L2 device** node. They may optionally expose via the :ref:`media controller API <media_controller>`. +.. note:: + + Devices that require **mc-centric** hardware control should report + a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag + (see :ref:`VIDIOC_QUERYCAP`). + + For **MC-centric** control, before using the V4L2 device, it is required to set the hardware pipelines via the :ref:`media controller API <media_controller>`. For those devices, the diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst b/Documentation/media/uapi/v4l/vidioc-querycap.rst index 12e0d9a63cd8..2b08723375bc 100644 --- a/Documentation/media/uapi/v4l/vidioc-querycap.rst +++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst @@ -252,6 +252,11 @@ specification the ioctl returns an ``EINVAL`` error code. * - ``V4L2_CAP_TOUCH`` - 0x10000000 - This is a touch device. + * - ``V4L2_MC_CENTRIC`` + - 0x20000000 + - Indicates that the device require **mc-centric** hardware + control, and thus can't be used by **v4l2-centric** applications. + See :ref:`v4l2_hardware_control` for more details. * - ``V4L2_CAP_DEVICE_CAPS`` - 0x80000000 - The driver fills the ``device_caps`` field. This capability can diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h index 45cf7359822c..7b490fe97980 100644 --- a/include/uapi/linux/videodev2.h +++ b/include/uapi/linux/videodev2.h @@ -460,6 +460,8 @@ struct v4l2_capability { #define V4L2_CAP_TOUCH 0x10000000 /* Is a touch device */ +#define V4L2_CAP_MC_CENTRIC 0x20000000 /* Device require mc-centric hardware control */ + #define V4L2_CAP_DEVICE_CAPS 0x80000000 /* sets device capabilities field */ /*