[PATCH 0/3] Add separate non-KMS state; constify struct drm_driver

[Daniel Vetter]

On Wed, Feb 26, 2020 at 06:39:08AM +0100, Thomas Zimmermann wrote:
> Hi
> 
> Am 25.02.20 um 18:44 schrieb Daniel Vetter:
> > On Tue, Feb 25, 2020 at 04:58:59PM +0100, Thomas Zimmermann wrote:
> >> This patchset moves legacy, non-KMS driver state from struct drm_driver
> >> into struct drm_legacy_state. Only non-KMS drivers provide an instance
> >> of the latter structure. One special case is nouveau, which supports
> >> legacy interfaces. It also provides an instance of the legacy state if
> >> the legacy interfaces have been enabled (i.e., defines the config option
> >> CONFIG_NOUVEAU_LEGACY_CTX_SUPPORT)
> >>
> >> I reviewed all call sites of legacy state and functions to verify that
> >> DRIVER_LEGACY or DRIVER_KMS_LEGACY_CONTEXT is set on the device; or that
> >> DRIVER_MODESET is not set.
> >>
> >> With the mutable KMS state removed, instances of struct drm_driver can
> >> be declared as constant. The patchset modifies the DRM core accordingly.
> >> Individual drivers can follow later on.
> > 
> > Bikeshed: We very much have modern non-KMS drivers (vgem, etnaviv, v3d,
> > panfrost, ...). non-KMS != legacy, which is what you're talking about
> > here.
> 
> OK, probably needs to be more precise.
> 
> > 
> > Other thing, and it's a bit raining on your parade: I don't see the point.
> > Sprinkling a few more #ifdef CONFIG_DRM_LEGACY over the relevant parts
> > sounds like a reasonable idea. But this is a lot of churn for drivers
> > which are all pretty much dead, and just waiting for their eventual
> > removal. And from a compile-testing pov of making sure modern drivers
> > don't use any of the deprecated stuff wrapping it in CONFIG_DRM_LEGACY
> > should be plenty enough.
> 
> It's not about these old drivers, it's about having constant driver
> structures and maybe saving a few bytes in the modern drivers. If these
> old drivers hold back improvements to the drivers we care about, I don't
> see we they are not to be touched.
> 
> This cannot be solved with CONFIG_DRM_LEGACY, unless you want to wrap
> any reference in core code to legacy data. I tried at first and it
> turned out to be an unreadable mess.

Laurent has a patch series to constify drm_driver for all !legacy drivers.
Without changing the world.

So yeah it's possible, we're not hurting ourselves here (aside from the
few bytes if we don't do the #ifdev CONFIG_DRM_LEGACY).

https://patchwork.freedesktop.org/series/73811/

> And from a complexity POV the patchset is trivial. It adds a data
> structure to each old driver and moves a few initializers around. The
> worst thing that can happen is that code tried to dereference the legacy
> pointer when it's not set. This bug will happen with modern drivers, so
> we should see it easily.

Laurent's series is even more trivial I think.
-Daniel

> 
> Best regards
> Thomas
> 
> > 
> > And from a "make stuff const" I think Laurent's much more minimal series
> > also gets us there for all the drivers we care about.
> > -Daniel
> > 
> >>
> >> Thomas Zimmermann (3):
> >>   drm: Add separate state structure for legacy, non-KMS drivers
> >>   drm: Move non-kms driver state into struct drm_legacy_state
> >>   drm: Constify struct drm_driver in DRM core
> >>
> >>  drivers/gpu/drm/drm_bufs.c            | 10 +++++-----
> >>  drivers/gpu/drm/drm_context.c         |  9 +++++----
> >>  drivers/gpu/drm/drm_drv.c             | 12 ++++++++----
> >>  drivers/gpu/drm/drm_file.c            |  4 ++--
> >>  drivers/gpu/drm/drm_legacy_misc.c     |  6 +++---
> >>  drivers/gpu/drm/drm_lock.c            |  7 ++++---
> >>  drivers/gpu/drm/drm_pci.c             | 16 ++++++++++------
> >>  drivers/gpu/drm/drm_vblank.c          | 11 ++++++-----
> >>  drivers/gpu/drm/i810/i810_drv.c       | 10 +++++++---
> >>  drivers/gpu/drm/mga/mga_drv.c         | 16 ++++++++++------
> >>  drivers/gpu/drm/nouveau/nouveau_drm.c |  8 ++++++++
> >>  drivers/gpu/drm/r128/r128_drv.c       | 16 ++++++++++------
> >>  drivers/gpu/drm/savage/savage_drv.c   | 12 ++++++++----
> >>  drivers/gpu/drm/sis/sis_drv.c         |  8 ++++++--
> >>  drivers/gpu/drm/tdfx/tdfx_drv.c       |  6 +++++-
> >>  drivers/gpu/drm/via/via_drv.c         | 16 ++++++++++------
> >>  include/drm/drm_device.h              |  2 +-
> >>  include/drm/drm_drv.h                 | 21 +++++----------------
> >>  include/drm/drm_legacy.h              | 27 +++++++++++++++++++++++----
> >>  include/drm/drm_pci.h                 |  4 ++--
> >>  20 files changed, 138 insertions(+), 83 deletions(-)
> >>
> >> --
> >> 2.25.0
> >>
> > 
> 
> -- 
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
> 




-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch