[PATCH v2 00/15] DRM fbconv helpers for converting fbdev drivers
Daniel Vetter
daniel at ffwll.ch
Tue Oct 15 14:33:18 UTC 2019
Hi Thomas,
On Mon, Oct 14, 2019 at 04:04:01PM +0200, Thomas Zimmermann wrote:
> (was: DRM driver for fbdev devices)
>
> This is version 2 of the fbdev conversion helpers. It's more or less a
> rewrite of the original patchset.
>
> The fbdev subsystem is considered legacy and will probably be removed at
> some point. This would mean the loss of a signifanct number of drivers.
> Some of the affected hardware is not in use any longer, but some hardware
> is still around and provides good(-enough) framebuffers.
>
> The fbconv helpers allow for running the current DRM stack on top of fbdev
> drivers. It's a set of functions that convert between fbdev interfaces and
> DRM interfaces. Based on SHMEM and simple KMS helpers, it only offers the
> basic functionality of a framebuffer, but should be compatible with most
> existing fbdev drivers.
>
> A DRM driver using fbconv helpers consists of
>
> * DRM stub code that calls into fbconv helpers, and
> * the original fbdev driver code.
>
> The fbdev driver code has to be modified to register itself with the
> stub driver instead of the fbdev core framework. A tutorial on how to use
> the helpers is part of this patchset. The resulting driver hybrid can be
> refactored into a first-class DRM driver. The fbconv helpers contain a
> number of comments, labeled 'DRM porting note', which explain the required
> steps.
>
> I tested the current patchset with the following drivers: atyfb, aty128fb,
> matroxfb, pm2fb, pm3fb, rivafb, s3fb, savagefb, sisfb, tdfxfb and tridentfb.
> With each, I was able to successfully start with fbcon enabled, run weston and
> X11. The drivers are available at [1]. For reference, the patchset includes
> the Matrox stub driver.
So I really don't want to rain on the parade here, since if you think this
is useful when converting fbdev drivers I'll buy that, and I'm all for
getting more modern drivers into drm.
But I have a bunch of concerns with the approach you're proposing here:
- we've tried staging for drm driver refactoring, it hurts. Separate tree
plus the quick pace in refactoring create lots of pains. And for small
drivers refacotoring before it's not buying you anything above
refactoring in your own personal tree. And for big drivers we're fairly
lenient with merging drivers that aren't fully polished yet, if there's
a team serious enough with cleaning up the mess. I think even merging
partial drivers directly under drivers/gpu (but behind CONFIG_BROKEN) is
better than staging.
- we've had conversion helpers before (for the legacy kms -> atomic
upgrade). They constantly broke, pretty much every release when someone
wanted to use them they first had to fix them up again. I think having
those helpers is good, but better to just have them in some branch
somewhere where it's clear that they might not work anymore on latest
upstream.
- especially for some of these simple fbdev drivers I feel like just
typing a new driver from scratch might be simpler.
A few more concerns specifically for your mga example:
- We already have a mga driver. Might be better to integrate support for
older mgas into that than have a parallel driver.
- Your helper is based on simple display pipe, and I think for these old
mga chips (especially the dual pipe mga 450 and 550) simple display pipe
helper is more a hindering detour than actual help. From a quick read
through the code (especially all the custom ioctls) you definitely want
separate TV-out connector to expose all the tv mode properties (instead
of the custom ioctls).
- On the topic of ioctls, looks like we could add FBIOGET_VBLANK to our
generic implementation in the fbdev helpers.
So here's my alternative proposal:
- You push this as a branch onto a gitlab repo (freedesktop.org or
wherever you feel like).
- You add a gitlab CI target to autobuild the very nice kerneldoc you've
created. Feel free to also do this with anything else you're familiar
with, it's just I know gitlab and it's real simple to get a few docs
autogenerated and published with it.
- We add a todo.rst patch linking to your branch and the docs and a few
lines on how to best convert an fbdev driver over to kms/atomic.
And all the drivers would land the usual way, like any of the other
drivers we've added to drivers/gpu/drm over the past few years.
Thoughts?
Cheers, Daniel
>
> v2:
> * rename to fbconv helpers
> * rewrite as helper library
> * switch over to simple KMS helpers
> * switch over to SHMEM
> * add documentation
>
> [1] https://gitlab.freedesktop.org/tzimmermann/linux/commits/fbconv-plus-drivers
>
> Thomas Zimmermann (15):
> fbdev: Export fb_check_foreignness()
> fbdev: Export FBPIXMAPSIZE
> drm/simple-kms-helper: Add mode_fixup() to simple display pipe
> drm: Add fbconv helper module
> drm/fbconv: Add DRM <-> fbdev pixel-format conversion
> drm/fbconv: Add mode conversion DRM <-> fbdev
> drm/fbconv: Add modesetting infrastructure
> drm/fbconv: Add plane-state check and update
> drm/fbconv: Mode-setting pipeline enable / disable
> drm/fbconv: Reimplement several fbdev interfaces
> drm/fbconv: Add helpers for init and cleanup of fb_info structures
> drm/fbconv: Add helper documentation
> staging: Add mgakms driver
> staging/mgakms: Import matroxfb driver source code
> staging/mgakms: Update matroxfb driver code for DRM
>
> Documentation/gpu/drm-kms-helpers.rst | 12 +
> Documentation/gpu/todo.rst | 15 +
> drivers/gpu/drm/Kconfig | 11 +
> drivers/gpu/drm/Makefile | 1 +
> drivers/gpu/drm/drm_fbconv_helper.c | 2126 +++++++++++++++++
> drivers/gpu/drm/drm_simple_kms_helper.c | 15 +
> drivers/staging/Kconfig | 2 +
> drivers/staging/Makefile | 1 +
> drivers/staging/mgakms/Kconfig | 18 +
> drivers/staging/mgakms/Makefile | 17 +
> drivers/staging/mgakms/g450_pll.c | 539 +++++
> drivers/staging/mgakms/g450_pll.h | 13 +
> drivers/staging/mgakms/i2c-matroxfb.c | 238 ++
> drivers/staging/mgakms/matroxfb_DAC1064.c | 1082 +++++++++
> drivers/staging/mgakms/matroxfb_DAC1064.h | 174 ++
> drivers/staging/mgakms/matroxfb_Ti3026.c | 746 ++++++
> drivers/staging/mgakms/matroxfb_Ti3026.h | 10 +
> drivers/staging/mgakms/matroxfb_accel.c | 519 +++++
> drivers/staging/mgakms/matroxfb_accel.h | 9 +
> drivers/staging/mgakms/matroxfb_base.c | 2592 +++++++++++++++++++++
> drivers/staging/mgakms/matroxfb_base.h | 700 ++++++
> drivers/staging/mgakms/matroxfb_crtc2.h | 35 +
> drivers/staging/mgakms/matroxfb_g450.c | 640 +++++
> drivers/staging/mgakms/matroxfb_g450.h | 10 +
> drivers/staging/mgakms/matroxfb_maven.h | 21 +
> drivers/staging/mgakms/matroxfb_misc.c | 815 +++++++
> drivers/staging/mgakms/matroxfb_misc.h | 22 +
> drivers/staging/mgakms/mga_device.c | 68 +
> drivers/staging/mgakms/mga_device.h | 30 +
> drivers/staging/mgakms/mga_drv.c | 129 +
> drivers/staging/mgakms/mga_drv.h | 14 +
> drivers/video/fbdev/core/fbmem.c | 5 +-
> include/drm/drm_fbconv_helper.h | 150 ++
> include/drm/drm_simple_kms_helper.h | 43 +
> include/linux/fb.h | 3 +
> 35 files changed, 10822 insertions(+), 3 deletions(-)
> create mode 100644 drivers/gpu/drm/drm_fbconv_helper.c
> create mode 100644 drivers/staging/mgakms/Kconfig
> create mode 100644 drivers/staging/mgakms/Makefile
> create mode 100644 drivers/staging/mgakms/g450_pll.c
> create mode 100644 drivers/staging/mgakms/g450_pll.h
> create mode 100644 drivers/staging/mgakms/i2c-matroxfb.c
> create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.c
> create mode 100644 drivers/staging/mgakms/matroxfb_DAC1064.h
> create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.c
> create mode 100644 drivers/staging/mgakms/matroxfb_Ti3026.h
> create mode 100644 drivers/staging/mgakms/matroxfb_accel.c
> create mode 100644 drivers/staging/mgakms/matroxfb_accel.h
> create mode 100644 drivers/staging/mgakms/matroxfb_base.c
> create mode 100644 drivers/staging/mgakms/matroxfb_base.h
> create mode 100644 drivers/staging/mgakms/matroxfb_crtc2.h
> create mode 100644 drivers/staging/mgakms/matroxfb_g450.c
> create mode 100644 drivers/staging/mgakms/matroxfb_g450.h
> create mode 100644 drivers/staging/mgakms/matroxfb_maven.h
> create mode 100644 drivers/staging/mgakms/matroxfb_misc.c
> create mode 100644 drivers/staging/mgakms/matroxfb_misc.h
> create mode 100644 drivers/staging/mgakms/mga_device.c
> create mode 100644 drivers/staging/mgakms/mga_device.h
> create mode 100644 drivers/staging/mgakms/mga_drv.c
> create mode 100644 drivers/staging/mgakms/mga_drv.h
> create mode 100644 include/drm/drm_fbconv_helper.h
>
> --
> 2.23.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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