linux-kernel - Re: [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers

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Message-ID: <87sgvfsty4.fsf@anholt.net>
Date:   Thu, 21 Mar 2019 16:12:35 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     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>,
        Eben Upton <eben@...pberrypi.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers

Paul Kocialkowski <paul.kocialkowski@...tlin.com> writes:

> Hi,
>
> Le mercredi 20 mars 2019 à 09:56 -0700, Eric Anholt a écrit :
>> Paul Kocialkowski <paul.kocialkowski@...tlin.com> writes:
>> 
>> > 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>
>> > ---
>> >  drivers/gpu/drm/drm_file.c | 3 +--
>> >  include/drm/drm_drv.h      | 2 +-
>> >  2 files changed, 2 insertions(+), 3 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) {
>> >  		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..aa14607e54d4 100644
>> > --- a/include/drm/drm_drv.h
>> > +++ b/include/drm/drm_drv.h
>> > @@ -236,7 +236,7 @@ struct drm_driver {
>> >  	 * 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.
>> > +	 * modern drivers can use it for other purposes only.
>> >  	 */
>> >  	void (*lastclose) (struct drm_device *);
>> 
>> Our usage in vc4 is not very different from what we called "hardware
>> initialization" in other devices.  I would rather just delete this
>> sentence entirely.
>
> Sounds good to me!

With the delete, the series is:

Reviewed-by: Eric Anholt <eric@...olt.net>

but hopefully someone other than a vc4 developer (danvet?) can make the
call on whether undeprecating firstopen/lastclose for this is
reasonable.

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