[Intel-gfx] [RFC v4 00/25] drm: Add generic fbdev emulation
Daniel Vetter
daniel at ffwll.ch
Mon Apr 16 08:21:12 UTC 2018
On Sat, Apr 14, 2018 at 01:52:53PM +0200, Noralf Trønnes wrote:
> This patchset explores the possibility of having generic fbdev emulation
> in DRM for drivers that supports dumb buffers which they can export. An
> API is added to support in-kernel clients in general.
>
> In this version I was able to reuse the modesetting code from
> drm_fb_helper in the client API. This avoids code duplication, carries
> over lessons learned and the modesetting code is bisectable. The
> downside is that it takes +10 patches to rip drm_fb_helper in two, so
> maybe it's not worth it wrt possible breakage and a challenging review.
So my idea wasn't to rip the fbdev helper in half first (that's indeed a
lot of work). But start out right away with using every piece of the
drm_client infrastructure you're adding in the existing fbdev code.
That way there's not a huge patch series which just adds code, with no
users, but every step of the way and every addition is tested almost right
away. That makes more gradual merging also easier. The things I have in
mind here is the generic fb_probe, or the drm_client block/unblock masters
and all that stuff.
Then, once we've demonstrated all these auxiliary pieces necessary for
drm_client.c work, we can cut the fb-helper in half and move the modeset
code into the drm_client library.
I still prefer an even more gradual path like this compared to what you
have in your patch series, but I understand that's yet another huge
shuffle. And the current series seems like a good enough approach to get
to essentially the same place.
> Does the Intel CI test the fbdev emulation?
We have fbdev emulation enabled, and iirc there's even a few tests for
fbdev. Just booting it on 20+ machines is a lot of testing itsefl already.
>
> Daniel had this concern with the previous version:
>
> The register/unregister model needs more thought. Allowing both clients
> to register whenever they want to, and drm_device instances to come and
> go is what fbcon has done, and the resulting locking is a horror show.
>
> I think if we require that all in-kernel drm_clients are registers when
> loading drm.ko (and enabled/disabled only per module options and
> Kconfig), then we can throw out all the locking. That avoids a lot of
> the headaches.
>
> I have solved this by adding a notifier that fires when a new DRM device
> is registered (I've removed the new() callback). Currently only
> bootsplash uses this. The fbdev client needs to be setup from the driver
> since it can't know on device registration if the driver will setup it's
> own fbdev emulation later and the vtcon client hooks up to a user
> provided device id.
Ugh, notifier is exactly what fbcon also uses. It just hides the locking
horror show slightly, but it's equally bad. I'm working on a multi-year
plan to rip out the fbcon notifier, please don't start another one. See
commit 6104c37094e729f3d4ce65797002112735d49cd1
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date: Tue Aug 1 17:32:07 2017 +0200
fbcon: Make fbcon a built-time depency for fbdev
for full details.
> Since fbcon can't handle fb_open failing, the buffer has to be
> pre-allocated. Exporting a GEM buffer pins the driver module making it
> impossible to unload it.
> I have included 2 solutions to the problem:
> - sysfs file to remove/close clients: remove_internal_clients
This is the same thing that defacto happens already with fbcon: You have
to remove fbcon first (which holds a full ref on the fbdev, which prevents
the drm driver from unloading). I think explicitly asking for that
reference to disappear is ok.
It does mean everyone has to update their unload scripts, but oh well.
> - Change drm_gem_prime_export() so it doesn't pin on client buffers
The double-loop in that patch definitely doesn't cut it, but worst case I
think something like that could be made to work.
> If a dumb buffer is exported from a kernel thread (worker) context, the
> file descriptor isn't closed and I leak a reference so the buffer isn't
> freed. Please look at drm_client_buffer_create() in patch
> 'drm/client: Finish the in-kernel client API'.
> This is a blocker that needs a solution.
Hm, missed that in my first cursory read of the series, I'l take another
look.
-Daniel
>
>
> Noralf.
>
> Changes since version 3:
> Client API changes:
> - Drop drm_client_register_funcs() which attached clients indirectly.
> Let clients attach directly using drm_client_new{_from_id}(). Clients
> that wants to attach to all devices must be linked into drm.ko and use
> the DRM device notifier. This is done to avoid the lock/race
> register/unregister hell we have with fbcon. (Daniel Vetter)
> - drm_client_display_restore() checks if there is a master and if so
> returns -EBUSY. (Daniel Vetter)
> - Allocate drm_file up front instead of on-demand. Since fbdev can't do
> on demand buffer allocation because of fbcon, there's no need for this.
> - Add sysfs file to remove clients
> - Don't pin driver module when exporting gem client buffers
> - Dropped page flip support since drm_fb_helper is now used for fbdev
> emulation.
>
> - The bootsplash client now switches over to fbdev on keypress.
>
> Changes since version 2:
> - Don't set drm master for in-kernel clients. (Daniel Vetter)
> - Add in-kernel client API
>
> Changes since version 1:
> - Don't add drm_fb_helper_fb_open() and drm_fb_helper_fb_release() to
> DRM_FB_HELPER_DEFAULT_OPS(). (Fi.CI.STATIC)
> The following uses that macro and sets fb_open/close: udlfb_ops,
> amdgpufb_ops, drm_fb_helper_generic_fbdev_ops, nouveau_fbcon_ops,
> nouveau_fbcon_sw_ops, radeonfb_ops.
> This results in: warning: Initializer entry defined twice
> - Support CONFIG_DRM_KMS_HELPER=m (kbuild test robot)
> ERROR: <function> [drivers/gpu/drm/drm_kms_helper.ko] undefined!
> - Drop buggy patch: (Chris Wilson)
> drm/prime: Clear drm_gem_object->dma_buf on release
> - Defer buffer creation until fb_open.
>
>
> David Herrmann (1):
> drm: provide management functions for drm_file
>
> Noralf Trønnes (24):
> drm/file: Don't set master on in-kernel clients
> drm/fb-helper: No need to cache rotation and sw_rotations
> drm/fb-helper: Remove drm_fb_helper_debug_enter/leave()
> drm/fb-helper: dpms_legacy(): Only set on connectors in use
> drm/atomic: Move __drm_atomic_helper_disable_plane/set_config()
> drm: Begin an API for in-kernel clients
> drm/fb-helper: Use struct drm_client_display
> drm/fb-helper: Move modeset commit code to drm_client
> drm/connector: Add
> drm_connector_has_preferred_mode/pick_cmdline_mode()
> drm/connector: Add connector array functions
> drm/i915: Add drm_driver->initial_client_display callback
> drm/fb-helper: Remove struct drm_fb_helper_crtc
> drm/fb-helper: Remove struct drm_fb_helper_connector
> drm/fb-helper: Move modeset config code to drm_client
> drm: Make ioctls available for in-kernel clients
> drm/client: Bail out if there's a DRM master
> drm/client: Make the display modes available to clients
> drm/client: Finish the in-kernel client API
> drm/prime: Don't pin module on export for in-kernel clients
> drm/fb-helper: Add drm_fb_helper_fb_open/release()
> drm/fb-helper: Add generic fbdev emulation
> drm: Add DRM device registered notifier
> drm/client: Hack: Add bootsplash
> drm/client: Hack: Add DRM VT console client
>
> drivers/gpu/drm/Kconfig | 2 +
> drivers/gpu/drm/Makefile | 4 +-
> drivers/gpu/drm/client/Kconfig | 14 +
> drivers/gpu/drm/client/Makefile | 3 +
> drivers/gpu/drm/client/drm_bootsplash.c | 248 ++++++
> drivers/gpu/drm/client/drm_vtcon.c | 785 +++++++++++++++++
> drivers/gpu/drm/client/internal.h | 19 +
> drivers/gpu/drm/drm_atomic.c | 168 ++++
> drivers/gpu/drm/drm_atomic_helper.c | 168 +---
> drivers/gpu/drm/drm_auth.c | 33 +
> drivers/gpu/drm/drm_client.c | 1448 +++++++++++++++++++++++++++++++
> drivers/gpu/drm/drm_connector.c | 199 +++++
> drivers/gpu/drm/drm_crtc_internal.h | 18 +-
> drivers/gpu/drm/drm_debugfs.c | 7 +
> drivers/gpu/drm/drm_drv.c | 43 +
> drivers/gpu/drm/drm_dumb_buffers.c | 33 +-
> drivers/gpu/drm/drm_fb_helper.c | 1420 ++++++++----------------------
> drivers/gpu/drm/drm_file.c | 304 ++++---
> drivers/gpu/drm/drm_framebuffer.c | 50 +-
> drivers/gpu/drm/drm_internal.h | 7 +
> drivers/gpu/drm/drm_ioc32.c | 2 +-
> drivers/gpu/drm/drm_ioctl.c | 4 +-
> drivers/gpu/drm/drm_prime.c | 37 +-
> drivers/gpu/drm/drm_probe_helper.c | 3 +
> drivers/gpu/drm/drm_sysfs.c | 20 +
> drivers/gpu/drm/i915/i915_drv.c | 1 +
> drivers/gpu/drm/i915/intel_drv.h | 11 +
> drivers/gpu/drm/i915/intel_fbdev.c | 112 +--
> include/drm/drm_atomic.h | 5 +
> include/drm/drm_atomic_helper.h | 4 -
> include/drm/drm_client.h | 182 ++++
> include/drm/drm_connector.h | 11 +
> include/drm/drm_device.h | 4 +
> include/drm/drm_drv.h | 25 +
> include/drm/drm_fb_helper.h | 126 ++-
> 35 files changed, 4007 insertions(+), 1513 deletions(-)
> create mode 100644 drivers/gpu/drm/client/Kconfig
> create mode 100644 drivers/gpu/drm/client/Makefile
> create mode 100644 drivers/gpu/drm/client/drm_bootsplash.c
> create mode 100644 drivers/gpu/drm/client/drm_vtcon.c
> create mode 100644 drivers/gpu/drm/client/internal.h
> create mode 100644 drivers/gpu/drm/drm_client.c
> create mode 100644 include/drm/drm_client.h
>
> --
> 2.15.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
More information about the Intel-gfx
mailing list