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From: Daniel Vetter <daniel@ffwll.ch>
To: "Noralf Trønnes" <noralf@tronnes.org>
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [RFC v4 00/25] drm: Add generic fbdev emulation
Date: Mon, 16 Apr 2018 10:21:12 +0200	[thread overview]
Message-ID: <20180416082112.GJ31310@phenom.ffwll.local> (raw)
In-Reply-To: <20180414115318.14500-1-noralf@tronnes.org>

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@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@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

  parent reply	other threads:[~2018-04-16  8:21 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-14 11:52 [RFC v4 00/25] drm: Add generic fbdev emulation Noralf Trønnes
2018-04-14 11:52 ` [RFC v4 01/25] drm: provide management functions for drm_file Noralf Trønnes
2018-04-14 11:52 ` [RFC v4 02/25] drm/file: Don't set master on in-kernel clients Noralf Trønnes
2018-04-14 11:52 ` [RFC v4 03/25] drm/fb-helper: No need to cache rotation and sw_rotations Noralf Trønnes
2018-04-14 11:52 ` [RFC v4 04/25] drm/fb-helper: Remove drm_fb_helper_debug_enter/leave() Noralf Trønnes
2018-04-14 11:52 ` [RFC v4 05/25] drm/fb-helper: dpms_legacy(): Only set on connectors in use Noralf Trønnes
2018-04-14 11:52 ` [RFC v4 06/25] drm/atomic: Move __drm_atomic_helper_disable_plane/set_config() Noralf Trønnes
2018-04-16  8:30   ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 07/25] drm: Begin an API for in-kernel clients Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 08/25] drm/fb-helper: Use struct drm_client_display Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 09/25] drm/fb-helper: Move modeset commit code to drm_client Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 10/25] drm/connector: Add drm_connector_has_preferred_mode/pick_cmdline_mode() Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 11/25] drm/connector: Add connector array functions Noralf Trønnes
2018-04-16  8:33   ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 12/25] drm/i915: Add drm_driver->initial_client_display callback Noralf Trønnes
2018-04-16  8:38   ` Daniel Vetter
2019-03-01 11:46     ` [Intel-gfx] " Noralf Trønnes
2019-03-01 11:51       ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 13/25] drm/fb-helper: Remove struct drm_fb_helper_crtc Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 14/25] drm/fb-helper: Remove struct drm_fb_helper_connector Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 15/25] drm/fb-helper: Move modeset config code to drm_client Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 16/25] drm: Make ioctls available for in-kernel clients Noralf Trønnes
2018-04-16  9:04   ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 17/25] drm/client: Bail out if there's a DRM master Noralf Trønnes
2018-04-16  8:45   ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 18/25] drm/client: Make the display modes available to clients Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 19/25] drm/client: Finish the in-kernel client API Noralf Trønnes
2018-04-16  8:27   ` [Intel-gfx] " Daniel Vetter
2018-04-16 15:58     ` Noralf Trønnes
2018-04-17  8:08       ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 20/25] drm/prime: Don't pin module on export for in-kernel clients Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 21/25] drm/fb-helper: Add drm_fb_helper_fb_open/release() Noralf Trønnes
2018-04-16  8:46   ` Daniel Vetter
2018-04-16 16:10     ` Noralf Trønnes
2018-04-17  8:14       ` [Intel-gfx] " Daniel Vetter
2018-04-14 11:53 ` [RFC v4 22/25] drm/fb-helper: Add generic fbdev emulation Noralf Trønnes
2018-04-16  8:52   ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 23/25] drm: Add DRM device registered notifier Noralf Trønnes
2018-04-17 10:16   ` Daniel Vetter
2018-04-14 11:53 ` [RFC v4 24/25] drm/client: Hack: Add bootsplash Noralf Trønnes
2018-04-14 11:53 ` [RFC v4 25/25] drm/client: Hack: Add DRM VT console client Noralf Trønnes
2018-04-16  8:21 ` Daniel Vetter [this message]
2018-04-16 18:49   ` [RFC v4 00/25] drm: Add generic fbdev emulation Noralf Trønnes
2018-04-17  8:10     ` [Intel-gfx] " Daniel Vetter
  -- strict thread matches above, loose matches on Subject: below --
2018-04-13 16:53 Noralf Trønnes
2018-04-13 17:06 ` Noralf Trønnes
2018-04-12 13:17 Noralf Trønnes
2018-04-12 16:34 ` Noralf Trønnes
2018-04-16  7:47   ` Daniel Vetter

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