[PATCH 03/12] drm: call ->firstopen() before ->open()

[Daniel Vetter]

On Thu, Jul 24, 2014 at 11:31:05AM +0200, David Herrmann wrote:
> Hi
> 
> On Wed, Jul 23, 2014 at 9:25 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Wed, Jul 23, 2014 at 05:26:38PM +0200, David Herrmann wrote:
> >> Lets order things correctly:
> >>  ->load()
> >>    ->fistopen()
> >>      ->open()
> >>      ->close()
> >>    ->lastclose()
> >>  ->unload()
> >>
> >> This doesn't change much as only savage and radeon use ->firstopen() and
> >> they just do map-initialization. Therefore, the global drm mutex makes
> >> sure there cannot be any other f_op between ->open() and ->firstopen().
> >> However, once we get rid of that lock, we really want ->firstopen() to
> >> initialize the device before ->open() is called.
> >>
> >> Furthermore, this fixes the clean-up path in drm_open(). We currently
> >> don't cleanup the drm_file object if ->firstopen() fails.
> >>
> >> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
> >> ---
> >>  drivers/gpu/drm/drm_fops.c | 139 +++++++++++++++++++++------------------------
> >>  include/drm/drmP.h         |   2 +-
> >>  2 files changed, 66 insertions(+), 75 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> >> index 021fe5d..8e73519 100644
> >> --- a/drivers/gpu/drm/drm_fops.c
> >> +++ b/drivers/gpu/drm/drm_fops.c
> >> @@ -45,7 +45,7 @@ EXPORT_SYMBOL(drm_global_mutex);
> >>
> >>  static int drm_open_helper(struct file *filp, struct drm_minor *minor);
> >>
> >> -static int drm_setup(struct drm_device * dev)
> >> +static int drm_firstopen(struct drm_device * dev)
> >
> > All the stuff in here is only for legacy drivers. Imo we should rename
> > this to drm_legacy_setup and hide it harder.
> >
> > Also touching the init ordering for ums drivers is a bit risky, I'd advise
> > against it. firstopen is officially dead for kms driver and really there's
> > nothing legit you can do in there. imx abused until they've switched over
> > to the component framework.
> >
> > I'd just drop this one tbh.
> 
> I did a driver audit when writing this patch, there're only 2 drivers
> using firstopen:
> 
>  * radeon_cp: sets two fields of dev_private and calls drm_addmap() on
> those. In lastclose(), it calls drm_rmmap()
>  * savage: sets several fields in dev_private, calls
> arch_phys_wc_add() for some regions and requests a drm-map for those
> via drm_addmap(). On lastclose(), it reverts exactly those steps.
> 
> Taking into account that firstopen() just runs with drm_device
> context, not with drm_file context, I really think we should be
> calling it _before_ doing ->open(). I even think the drivers would
> fail horribly if we don't do this patch and some other user-context
> sneaks in between both calls (currently impossible thanks to
> drm_global_mutex).
> 
> Both ->firstopen() callbacks are fairly trivial. In favor of making
> the error-paths work in drm_open() I'd really like to get this in.
> This patch is preparing for my drm_file rework that can make
> drm_dev_unregister() stop all open files immediately.
> 
> But I honestly don't care much for UMS drivers, so if you NACK this,
> I'd just ignore the error code and add a comment that we don't do
> error-handling for UMS.

Yeah, I prefer just labels for dragons instead of poking them ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch