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

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Message-ID: <87zhpph4c2.fsf@anholt.net>
Date:   Wed, 20 Mar 2019 09:56:45 -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>,
        Paul Kocialkowski <paul.kocialkowski@...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:

> 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.

The only alternative I can think of to using a firstopen/lastclose-style
allocation for this would be to allocate the bin bo on the first
(non-dumb?) V3D BO allocation and refcount those to free the binner.

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