Em Wed, 27 Jan 2016 13:44:44 +0200 Sakari Ailus <sakari.ailus@xxxxxx> escreveu: > Hi Mauro, > > I see that this patch got applied to the media_tree master, but then > reverted a few days ago. For Kernel 4.5, the new ioctl is disabled. It was reverted after pulling back from Linus tree, in order to allow the developers to be able to test it and improve it if needed. So, the revert patch is meant to reach upstream only in Kernel 4.6, as proposed in this patch. It means that we have about 2 months to polite it before the next merge window. > Do you think the G_TOPOLOGY IOCTL and the > associated user space structs are ready for being included in a release? Well, the only doubt we had so far is about how to make it compatible with 64 bits kernelspace and 32 bits userspace. 2 months seems more than enough for us to properly address that. > > I have a few concerns over the current interface, in decreasing order of > importance: Ok, that's the first time you come with that. I still think that those could be addressed in the next 2 months, but, if not, we may eventually postpone enabling G_TOPOLOGY ioctl further. > > - G_TOPOLOGY IOCTL is intended to enable dynamic updates, but do we have a > driver actually supporting this? Laurent requested to postpone dynamic updates at the early stages of the MC patchset review. The initial patchset were using krefs to handle it. We can work on adding support for it for 4.6. I'm actually working today to add MC support on em28xx USB hardware. On such driver, there is a master driver (em28xx) and several sub-drivers (em28xx-video, em28xx-dvb, em28xx-alsa and em28xx-input). The sub-drivers are loaded asynchronously. meaning that the topology will be dynamically updated during driver load. The alsa module (or snd-usb-audio - depending on the hardware) can be unbind/rebind dynamically. So, while the hardware itself is not dynamic, dynamic support is needed, in order to avoid race conditions. > For instance, supposing that the users's > knowledge of the graph state isn't what the user expected it to be > (assuming the graph state changed between G_TOPOLOGY and SETUP_LINK), does > the user still want to perform the SETUP_LINK IOCTL or would the user > prefer that the kernel returned an error instead to tell the user has no > knowledge of the current graph state? I'd like to see how that works in > practice. For instance, a virtual driver such as vivi, but with MC, V4L2 > sub-device and V4L2 support which adds and removes a random entity every, > say, five minutes, would be wonderful. If this has not been tried out in a > real use case, the chances of getting it right may remain rather slim. It can be simulated by removing/adding or binding/unbinding snd-usb-audio module. We may also apply the virtual MC driver, if it is ready. Not sure about its current review stage of the virtual driver. > - struct media_v2_pad contains fields called "id" and "entity_id". The "id" > field, as far as I understand, is the graph object id, not the pad index. > In order to configure a link using MEDIA_IOC_SETUP_LINK, one does need to > know the entity id and the pad index. This information you'll only get > using MEDIA_IOC_ENUM_LINKS, which right now refutes the very purpose of > the G_TOPOLOGY IOCTL. Knowing the pad indices is also essential for the > V4L2 sub-device user space API. (I remember whether or not the pad index > should be there but I don't remember the details, except that it was > intentionally left out. Considering this again, I think adding it is > unavoidable.) A new ioctl to setup links is required, as we want to be able to change the status of multiple links at once. The thing with the PAD index is that it should be replaced by something more generic, via the properties API. On some cases, just an index is enough (when the pads are, for example, the output pins of a demux). But, in general, what an application would want is to specify the "audio out pin" or the "video out pin" of a device. As the index number may vary depending on the specific device, Such application should not have the index numbers hardcoded on it, but, instead, they should discover it via the userspace API. What we've agreed is that such information would be coded as a property via the properties API. > This together with the above point suggest there are no > real applications using G_TOPOLOGY yet. MEDIA_IOC_SETUP_LINK is a must only for subdev-centric hardware, like OMAP3. For device-node-centric hardware (like em28xx, au0828, etc), G_TOPOLOGY itself is useful to allow describing the hardware interfaces and their connections, e. g. to reimplement libmedia_dev at v4l-utils to use MC instead of sysfs. > - Some more thought should be given to the state of the reserved fields, in > e.g. struct media_v2_pad there are __u32 fields only, except a reserved > field which is a __u16 array of 9. While this isn't exactly wrong it makes > no sense either. Well, 2 months is enough for us to address the reserved fields ;) > - KernelDoc documentation would be nice for the G_TOPOLOGY argument structs. > DocBook documentation for G_TOPOLOGY as itself is fine, but I think it > reflects an older version of the structs than what's now defined in > include/uapi/linux/media.h. See: https://linuxtv.org/downloads/v4l-dvb-apis/media-g-topology.html Indeed, there is one missing struct there (media_v2_link). Not sure what happened here. I guess I lost one hunk when I wrote the KernelDoc patch. Anyway, adding it is easy. I'll prepare a patch for it soon. The description of media_v2_topology actually matches our last discussion (where we decided to not use any _reserved field there). Yet, this difference is actually the reason why we've delayed it in the first place, as my guts tell that we need more discussions about it. > Please give some thought on this. There are some obvious gaps that need to > be filled, and when doing so, I don't think we want to start guessing > whether there might be an application that depends on the current API/ABI. > > If you'd like the G_TOPOLOGY IOCTL and its argument structs to be available > for developers without kernel changes, I propose to add a new Kconfig option > for G_TOPOLOGY and make it depend on BROKEN. > > What do you think? Making it depending on BROKEN at our development tree is not a good thing, as BROKEN is not an option that can be changed with make menuconfig/xconfig. It needs to be easy to do tests on our development tree, in order for it to be tested by a broader audience. Ok, if we end by needing to postpone it even further, we could do something different, but it sounds to early to do that, as we can postpone such decision to happen closer to the next merge window (or even to happen just before releasing Kernel 4.6, if we discover too late some real issue there). > > On Mon, Jan 11, 2016 at 12:41:02PM -0200, Mauro Carvalho Chehab wrote: > > There are a few discussions left with regards to this ioctl: > > > > 1) the name of the new structs will contain _v2_ on it? > > 2) what's the best alternative to avoid compat32 issues? > > > > Due to that, let's postpone the addition of this new ioctl to > > the next Kernel version, to give people more time to discuss it. > > > > Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx> > > --- > > > > v2: Fix a compilation breakage > > > > Documentation/DocBook/media/v4l/media-ioc-g-topology.xml | 3 +++ > > drivers/media/media-device.c | 7 ++++++- > > include/uapi/linux/media.h | 6 +++++- > > 3 files changed, 14 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/DocBook/media/v4l/media-ioc-g-topology.xml b/Documentation/DocBook/media/v4l/media-ioc-g-topology.xml > > index e0d49fa329f0..63152ab9efba 100644 > > --- a/Documentation/DocBook/media/v4l/media-ioc-g-topology.xml > > +++ b/Documentation/DocBook/media/v4l/media-ioc-g-topology.xml > > @@ -48,6 +48,9 @@ > > > > <refsect1> > > <title>Description</title> > > + > > + <para><emphasis role="bold">NOTE:</emphasis> This new ioctl is programmed to be added on Kernel 4.6. Its definition/arguments may change until its final version.</para> > > + > > <para>The typical usage of this ioctl is to call it twice. > > On the first call, the structure defined at &media-v2-topology; should > > be zeroed. At return, if no errors happen, this ioctl will return the > > diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c > > index 4d1c13de494b..7dae0ac0f3ae 100644 > > --- a/drivers/media/media-device.c > > +++ b/drivers/media/media-device.c > > @@ -234,6 +234,7 @@ static long media_device_setup_link(struct media_device *mdev, > > return ret; > > } > > > > +#if 0 /* Let's postpone it to Kernel 4.6 */ > > static long __media_device_get_topology(struct media_device *mdev, > > struct media_v2_topology *topo) > > { > > @@ -389,6 +390,7 @@ static long media_device_get_topology(struct media_device *mdev, > > > > return 0; > > } > > +#endif > > > > static long media_device_ioctl(struct file *filp, unsigned int cmd, > > unsigned long arg) > > @@ -422,13 +424,14 @@ static long media_device_ioctl(struct file *filp, unsigned int cmd, > > mutex_unlock(&dev->graph_mutex); > > break; > > > > +#if 0 /* Let's postpone it to Kernel 4.6 */ > > case MEDIA_IOC_G_TOPOLOGY: > > mutex_lock(&dev->graph_mutex); > > ret = media_device_get_topology(dev, > > (struct media_v2_topology __user *)arg); > > mutex_unlock(&dev->graph_mutex); > > break; > > - > > +#endif > > default: > > ret = -ENOIOCTLCMD; > > } > > @@ -477,7 +480,9 @@ static long media_device_compat_ioctl(struct file *filp, unsigned int cmd, > > case MEDIA_IOC_DEVICE_INFO: > > case MEDIA_IOC_ENUM_ENTITIES: > > case MEDIA_IOC_SETUP_LINK: > > +#if 0 /* Let's postpone it to Kernel 4.6 */ > > case MEDIA_IOC_G_TOPOLOGY: > > +#endif > > return media_device_ioctl(filp, cmd, arg); > > > > case MEDIA_IOC_ENUM_LINKS32: > > diff --git a/include/uapi/linux/media.h b/include/uapi/linux/media.h > > index 5dbb208e5451..1e3c8cb43bd7 100644 > > --- a/include/uapi/linux/media.h > > +++ b/include/uapi/linux/media.h > > @@ -286,7 +286,7 @@ struct media_links_enum { > > * later, before the adding this API upstream. > > */ > > > > - > > +#if 0 /* Let's postpone it to Kernel 4.6 */ > > struct media_v2_entity { > > __u32 id; > > char name[64]; /* FIXME: move to a property? (RFC says so) */ > > @@ -351,6 +351,7 @@ static inline void __user *media_get_uptr(__u64 arg) > > { > > return (void __user *)(uintptr_t)arg; > > } > > +#endif > > > > /* ioctls */ > > > > @@ -358,6 +359,9 @@ static inline void __user *media_get_uptr(__u64 arg) > > #define MEDIA_IOC_ENUM_ENTITIES _IOWR('|', 0x01, struct media_entity_desc) > > #define MEDIA_IOC_ENUM_LINKS _IOWR('|', 0x02, struct media_links_enum) > > #define MEDIA_IOC_SETUP_LINK _IOWR('|', 0x03, struct media_link_desc) > > + > > +#if 0 /* Let's postpone it to Kernel 4.6 */ > > #define MEDIA_IOC_G_TOPOLOGY _IOWR('|', 0x04, struct media_v2_topology) > > +#endif > > > > #endif /* __LINUX_MEDIA_H */ > -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
