linux-kernel - Re: [PATCH v3 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers

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Date:   Fri, 29 Mar 2019 09:37:52 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Eric Anholt <eric@...olt.net>,
        Eben Upton <eben@...pberrypi.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v3 1/2] drm/file: Rehabilitate the firstopen hook for
 non-legacy drivers

On Fri, Mar 29, 2019 at 09:35:34AM +0100, Daniel Vetter wrote:
> On Thu, Mar 28, 2019 at 05:13:05PM +0100, Paul Kocialkowski wrote:
> > The firstopen DRM driver hook was initially used to perform hardware
> > initialization, which is now considered legacy. Only a single user of
> > firstopen remains at this point (savage).
> > 
> > In some specific cases, non-legacy drivers may also need to implement
> > these hooks. For instance on VC4, we need to allocate a 16 MiB buffer
> > for the GPU. Because it's not required for fbcon, it's a waste to
> > allocate it before userspace starts using the DRM device.
> > 
> > Using firstopen and lastclose for this allocation seems like the best
> > fit, so re-habilitate the hook to allow it to be called for non-legacy
> > drivers.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > Reviewed-by: Eric Anholt <eric@...olt.net>
> > ---
> >  drivers/gpu/drm/drm_file.c | 3 +--
> >  include/drm/drm_drv.h      | 3 ---
> >  2 files changed, 1 insertion(+), 5 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> > index b1838a41ad43..c011b5cbfb6b 100644
> > --- a/drivers/gpu/drm/drm_file.c
> > +++ b/drivers/gpu/drm/drm_file.c
> > @@ -266,8 +266,7 @@ static int drm_setup(struct drm_device * dev)
> >  {
> >  	int ret;
> >  
> > -	if (dev->driver->firstopen &&
> > -	    drm_core_check_feature(dev, DRIVER_LEGACY)) {
> > +	if (dev->driver->firstopen) {
> 
> If you guys insist on this (still not a fan myself) pls pull it out of
> drm_setup - that's all just legacy hw setup in there. I still think
> tracking this a bit more accurately (if you want to bother with this)
> would be better.

Maybe another one: Firstopen is called after ->open, which might be
confusing. But we can't change that ever because legacy drivers surely
rely on that somewhere (like the backwards load/unload calling sequence).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch