Re: [PATCH v7] unstable/drm-lease: DRM lease protocol support

On Thu, 17 Oct 2019 13:45:27 -0400 Drew DeVault sir@cmpwn.com wrote:

From: Marius Vlad marius.vlad@collabora.com

DRM leasing is a feature which allows the DRM master to "lease" a subset of its DRM resources to another DRM master via drmModeCreateLease, which returns a file descriptor for the new DRM master. We use this protocol to negotiate the terms of the lease and transfer this file descriptor to clients.

In less DRM-specific terms: this protocol allows Wayland compositors to give over their GPU resources (like displays) to a Wayland client to exclusively control.

The primary use-case for this is Virtual Reality headsets, which via the non-desktop DRM property are generally not used as desktop displays by Wayland compositors, and for latency reasons (among others) are most useful to games et al if they have direct control over the DRM resources associated with it. Basically, these are peripherals which are of no use to the compositor and may be of use to a client, but since they are tied up in DRM we need to use DRM leasing to get them into client's hands.

Signed-off-by: Marius Vlad marius.vlad@collabora.com Signed-off-by: Drew DeVault sir@cmpwn.com

---

v7's main change is that, upon binding to the drm_lease_manager, the server now sends along a non-master DRM fd for the client to use to enumerate resources. For this reason, the EDID event has been removed from the connector interface, under the assumption that clients who want to examine the EDID will line the connnector ID up with the appropriate resources from DRM.

Hi Drew,

thanks for this, I really hope it works out since the protocol is so neat and tidy now.

One thing I did not know the last time was that apparently systemd-logind may not like to give out non-master DRM fds. That might need fixing in logind implementations. I hope someone would step up to look into that.

I'm CC'ing dri-devel and Daniel Vetter to get some kernel side review for the non-master DRM fd idea:

This protocol aims to deliver a harmless "read-only" DRM device file description to a client, so that the client can enumerate all DRM resources, fetch EDID and other properties to be able to decide which connector it would want to lease. The client should not be able to change any KMS state through this fd, and it should not be able to e.g. spy on display contents. The assumption is that a non-master DRM fd from a fresh open() would be fine for this, but is it?

If it is not, could we make one that is? Simply giving out an fd for the client to inspect with standard DRM ioctls is just so convenient.

**

I wouldn't mind if the below links were part of the proper commit message.

Updated patches are available for:

wlroots: https://github.com/swaywm/wlroots/pull/1730 sway: https://github.com/swaywm/sway/pull/4289 kmscube: https://git.sr.ht/~sircmpwn/kmscube Xwayland: https://gitlab.freedesktop.org/xorg/xserver/merge_requests/248

Additionally, the Vulkan extension has been polished up:

https://github.com/KhronosGroup/Vulkan-Docs/pull/1001

A new implementation for Mesa's Vulkan WSI implementation will be available soon, as well as an implementation of the Wayland extension for Monado.

Makefile.am | 1 + unstable/drm-lease/README | 5 + unstable/drm-lease/drm-lease-unstable-v1.xml | 246 +++++++++++++++++++ 3 files changed, 252 insertions(+) create mode 100644 unstable/drm-lease/README create mode 100644 unstable/drm-lease/drm-lease-unstable-v1.xml

diff --git a/Makefile.am b/Makefile.am index 345ae6a..d9fff89 100644 --- a/Makefile.am +++ b/Makefile.am @@ -4,6 +4,7 @@ unstable_protocols = \ unstable/pointer-gestures/pointer-gestures-unstable-v1.xml \ unstable/fullscreen-shell/fullscreen-shell-unstable-v1.xml \ unstable/linux-dmabuf/linux-dmabuf-unstable-v1.xml \

• unstable/drm-lease/drm-lease-unstable-v1.xml \ unstable/text-input/text-input-unstable-v1.xml \ unstable/text-input/text-input-unstable-v3.xml \ unstable/input-method/input-method-unstable-v1.xml \

diff --git a/unstable/drm-lease/README b/unstable/drm-lease/README new file mode 100644 index 0000000..16f8551 --- /dev/null +++ b/unstable/drm-lease/README @@ -0,0 +1,5 @@ +Linux DRM lease

+Maintainers: +Drew DeVault sir@cmpwn.com +Marius Vlad marius-cristian.vlad@nxp.com

Marius' email address probably needs refreshing?

diff --git a/unstable/drm-lease/drm-lease-unstable-v1.xml b/unstable/drm-lease/drm-lease-unstable-v1.xml new file mode 100644 index 0000000..5fbc0e3 --- /dev/null +++ b/unstable/drm-lease/drm-lease-unstable-v1.xml @@ -0,0 +1,246 @@ +<?xml version="1.0" encoding="UTF-8"?> +<protocol name="drm_lease_unstable_v1">

• <copyright>

• Copyright © 2018 NXP
• Copyright © 2019 Status Research &amp; Development GmbH.
• Permission is hereby granted, free of charge, to any person obtaining a
• copy of this software and associated documentation files (the "Software"),
• to deal in the Software without restriction, including without limitation
• the rights to use, copy, modify, merge, publish, distribute, sublicense,
• and/or sell copies of the Software, and to permit persons to whom the
• Software is furnished to do so, subject to the following conditions:
• The above copyright notice and this permission notice (including the next
• paragraph) shall be included in all copies or substantial portions of the
• Software.
• THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
• IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
• FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
• THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
• LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
• FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
• DEALINGS IN THE SOFTWARE.

• </copyright>

• <interface name="zwp_drm_lease_manager_v1" version="1">

• <description summary="lease manager">

•  This protocol is used by Wayland compositors which act as Direct
  

•  Renderering Manager (DRM) masters to lease DRM resources to Wayland
  

•  clients. Once leased, the compositor will not use the leased resources
  

•  until the lease is revoked or the client closes the file descriptor. The
  

•  compositor will advertise one zwp_drm_lease_manager_v1 for each DRM node
  

•  which has resources available for leasing.
  

Ok, that takes care of the multi-card case. It also nicely identifies which device a connector is from.

•  The lease manager is used to advertise connectors which are available for
  

•  leasing, and by the client to negotiate a lease request.
  

•  Warning! The protocol described in this file is experimental and
  

•  backward incompatible changes may be made. Backward compatible changes
  

•  may be added together with the corresponding interface version bump.
  

•  Backward incompatible changes are done by bumping the version number in
  

•  the protocol and interface names and resetting the interface version.
  

•  Once the protocol is to be declared stable, the 'z' prefix and the
  

•  version number in the protocol and interface names are removed and the
  

•  interface version number is reset.
  

• </description>

• <enum name="error">

•  <entry name="stopped_manager" value="0"
  

•    summary="request sent to a manager which has been stopped"/>
  

• </enum>

• <request name="create_lease_request">

•  <description summary="create a lease request object">
  

•    Creates a lease request object.
  

•    See the documentation for zwp_drm_lease_request_v1 for details.
  

•  </description>
  

•  <arg name="id" type="new_id" interface="zwp_drm_lease_request_v1" />
  

• </request>

• <request name="stop">

•  <description summary="stop sending events">
  

•    Indicates the client no longer wishes to receive connector events. The
  

•    compositor may still send connector events until it sends the finish
  

•    event, however.
  

•    The client must not send any requests after this one.
  

•  </description>
  

• </request>

• <event name="drm_fd">

•  <description summary="open a non-master fd for this DRM node">
  

•    The compositor will send this event when the zwp_drm_lease_manager_v1
  

•    global is bound. The included fd is a non-master DRM file descriptor
  

•    opened for this device. The purpose of this event is to give the client
  

•    the ability to query DRM and discover information which may help them
  

•    pick the appropriate DRM device or select the appropriate connectors
  

•    therein.
  

•  </description>
  

•  <arg name="fd" type="fd" summary="DRM file descriptor" />
  

• </event>

• <event name="connector">

•  <description summary="advertise connectors available for leases">
  

•    The compositor may choose to advertise 0 or more connectors which may be
  

•    leased to clients, and will use this event to do so. This object may be
  

•    passed into a lease request to lease that connector. See
  

•    zwp_drm_lease_request_v1.add_connector for details.
  

•    When this global is bound, the compositor will send all connectors
  

•    available for lease, but may send additional connectors at any time.
  

•  </description>
  

•  <arg name="id" type="new_id" interface="zwp_drm_lease_connector_v1" />
  

• </event>

• <event name="finished">

•  <description summary="the compositor has finished using the manager">
  

•    This event indicates that the compositor is done sending connector
  

•    events. The compositor will destroy this object immediately after
  

•    sending this event, and it will become invalid. The client should
  

•    release any resources associated with this manager after receiving this
  

•    event.
  

•  </description>
  

• </event>

• </interface>

• <interface name="zwp_drm_lease_connector_v1" version="1">

• <description summary="a leasable DRM connector">

•  Represents a DRM connector which is available for lease. These objects are
  

•  created via zwp_drm_lease_manager_v1.connector, and should be passed into
  

•  lease requests via zwp_drm_lease_request_v1.add_connector.
  

• </description>

• <event name="name">

•  <description summary="name">
  

•    The compositor sends this event once the connector is created to
  

•    indicate the name of this connector. This will not change for the
  

•    duration of the Wayland session, but is not guaranteed to be consistent
  

•    between sessions.
  

•    If the compositor also supports zxdg_output_manager_v1 and this
  

•    connector corresponds to a zxdg_output_v1, this name will match the
  

•    name of this zxdg_output_v1 object.
  

•  </description>
  

•  <arg name="name" type="string" summary="connector name" />
  

• </event>

• <event name="description">

•  <description summary="description">
  

•    The compositor sends this event once the connector is created to provide
  

•    a human-readable description for this connector, which may be presented
  

•    to the user.
  

•  </description>
  

•  <arg name="description" type="string" summary="connector description" />
  

• </event>

• <event name="connector_id">

•  <description summary="connector_id">
  

•    The compositor will send this event to indicate the DRM ID which
  

•    represents the underlying connector which is being offered. Note that
  

•    the final lease may include additional object IDs, such as CRTCs and
  

•    planes.
  

•  </description>
  

•  <arg name="connector_id" type="int" summary="DRM Connector ID" />
  

• </event>

• <event name="withdrawn">

•  <description summary="lease offer withdrawn">
  

•    Sent to indicate that the compositor will no longer honor requests for
  

•    DRM leases which include this connector. The client may still issue a
  

•    lease request including this connector, but the compositor will send
  

•    zwp_drm_lease_v1.finished without issuing a lease fd.
  

•  </description>
  

• </event>

• <request name="destroy" type="destructor">

•  <description summary="destroy connector">
  

•    The client may send this request to indicate that it will not issue a
  

•    lease request for this connector. Clients are encouraged to send this
  

•    after receiving the "withdrawn" request so that the server can release
  

•    the resources associated with this connector offer.
  

•  </description>
  

• </request>

• </interface>

• <interface name="zwp_drm_lease_request_v1" version="1">

• <description summary="DRM lease request">

•  A client that wishes to lease DRM resources will attach the list of
  

•  connectors advertised with zwp_drm_lease_manager_v1.connector that they
  

•  wish to lease, then use zwp_drm_lease_request_v1.submit to submit the
  

•  request.
  

• </description>

• <enum name="error">

•  <entry name="submitted_lease" value="0"
  

•    summary="attempted to reuse a submitted lease"/>
  

• </enum>

• <request name="destroy" type="destructor">

•  <description summary="destroys the lease request object">
  

•    Indicates that the client will no longer use this lease request.
  

•  </description>
  

• </request>

• <request name="request_connector">

•   <description summary="request a connector for this lease">
  

•     Indicates that the client would like to lease the given connector.
  

•     This is only used as a suggestion, the compositor may choose to
  

•     include any resources in the lease it issues, or change the set of
  

•     leased resources at any time.
  

•   </description>
  

•   <arg name="connector" type="object"
  

•     interface="zwp_drm_lease_connector_v1" />
  

Don't we need a protocol error defined for the case, where the client uses a zwp_drm_lease_connector_v1 from a different global? That is, attempting to lease a connector from the wrong device.

If that was an error, then it would make sure that one cannot lease a mix across multiple devices in one go. I don't think leasing a mix across multiple devices could work, given only one DRM lease fd should be delivered.

• </request>

• <request name="submit">

•   <description summary="submit the lease request">
  

•     Submits the lease request and creates a new zwp_drm_lease_v1 object.
  

•     After calling submit, issuing any other request than destroy is a
  

•     protocol error.
  

•   </description>
  

•   <arg name="id" type="new_id" interface="zwp_drm_lease_v1" />
  

• </request>

• </interface>

• <interface name="zwp_drm_lease_v1" version="1">

• <description summary="a DRM lease">

•  A DRM lease object is used to transfer the DRM file descriptor to the
  

•  client and manage the lifetime of the lease.
  

• </description>

• <event name="lease_fd">

•  <description summary="shares the DRM file descriptor">
  

•    This event returns a file descriptor suitable for use with DRM-related
  

•    ioctls. The client should use drmModeGetLease to enumerate the DRM
  

•    objects which have been leased to them. If the compositor cannot or
  

Isn't the wording about drmModeGetLease() wrong here? The client can only see the leased resources through that fd, no matter what it does, right?

•    will not grant a lease for the requested connectors, it will not send
  

•    this event, instead sending the finished event immediately.
  

•    It is a protocol error for the compositor to send this event more than
  

•    once for a given lease.
  

•  </description>
  

•  <arg name="leased_fd" type="fd" summary="leased DRM file descriptor" />
  

• </event>

• <event name="finished">

•  <description summary="sent when the lease has been revoked">
  

•    When the compositor revokes the lease, it will issue this event to
  

•    notify clients of the change. If the client requires a new lease, they
  

•    should destroy this object and submit a new lease request. The
  

•    compositor will send no further events for this object after sending
  

•    the finish event.
  

•  </description>
  

• </event>

• <request name="destroy" type="destructor">

•  <description summary="destroys the lease object">
  

•    The client should send this to indicate that it no longer wishes to use
  

•    this lease. The compositor should use drmModeRevokeLease on the
  

•    appropriate file descriptor, if necessary, then release this object.
  

•  </description>
  

• </request>

• </interface>

+</protocol>

This seems to be in a very good shape now.

Thanks, pq