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

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Message-ID: <95645eb463840faf32bae284c16af443cc62f8a8.camel@bootlin.com>
Date:   Fri, 29 Mar 2019 09:38:19 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Daniel Vetter <daniel@...ll.ch>
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>,
        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

Hi Daniel,

On Fri, 2019-03-29 at 09:35 +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.

I sent out this v3 right before receiving your comments on v2, so this
new iteration only takes Eric's comments into account.

I think the points you made on v2 are very legitimate and I'll be
working to prepare a new series that takes them into consideration :)

Cheers,

Paul

> -Daniel
> 
> >  		ret = dev->driver->firstopen(dev);
> >  		if (ret != 0)
> >  			return ret;
> > diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> > index ca46a45a9cce..de5637494503 100644
> > --- a/include/drm/drm_drv.h
> > +++ b/include/drm/drm_drv.h
> > @@ -234,9 +234,6 @@ struct drm_driver {
> >  	 * kernel driver does not really own the hardware. Instead ownershipe is
> >  	 * handled with the help of userspace through an inheritedly racy dance
> >  	 * to set/unset the VT into raw mode.
> > -	 *
> > -	 * Legacy drivers initialize the hardware in the @firstopen callback,
> > -	 * which isn't even called for modern drivers.
> >  	 */
> >  	void (*lastclose) (struct drm_device *);
> >  
> > -- 
> > 2.21.0
> > 
-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com