linux-kernel - Re: [PATCH v8 3/3] drm: writeback: Add client capability for exposing writeback connectors

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Message-ID: <20180523122716.GF1582@e110455-lin.cambridge.arm.com>
Date:   Wed, 23 May 2018 13:27:17 +0100
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     Gustavo Padovan <gustavo@...ovan.org>,
        Sean Paul <seanpaul@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        David Airlie <airlied@...ux.ie>,
        Brian Starkey <brian.starkey@....com>,
        Alexandru-Cosmin Gheorghe <alexandru-cosmin.gheorghe@....com>,
        Eric Anholt <eric@...olt.net>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Daniel Stone <daniels@...labora.com>
Subject: Re: [PATCH v8 3/3] drm: writeback: Add client capability for
 exposing writeback connectors

On Wed, May 23, 2018 at 11:34:32AM +0200, Maarten Lankhorst wrote:
> Op 18-05-18 om 17:17 schreef Liviu Dudau:
> > Due to the fact that writeback connectors behave in a special way
> > in DRM (they always report being disconnected) we might confuse some
> > userspace. Add a client capability for writeback connectors that will
> > filter them out for clients that don't understand the capability.
> >
> > Re-requested-by: Sean Paul <seanpaul@...omium.org>
> > Cc: Brian Starkey <brian.starkey@....com>
> > Signed-off-by: Liviu Dudau <liviu.dudau@....com>
> > ---
> >  drivers/gpu/drm/drm_ioctl.c       | 7 +++++++
> >  drivers/gpu/drm/drm_mode_config.c | 5 +++++
> >  include/drm/drm_file.h            | 7 +++++++
> >  include/uapi/drm/drm.h            | 9 +++++++++
> >  4 files changed, 28 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
> > index af782911c505d..59951ff3e3630 100644
> > --- a/drivers/gpu/drm/drm_ioctl.c
> > +++ b/drivers/gpu/drm/drm_ioctl.c
> > @@ -325,6 +325,13 @@ drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
> >  		file_priv->atomic = req->value;
> >  		file_priv->universal_planes = req->value;
> >  		break;
> > +	case DRM_CLIENT_CAP_WRITEBACK_CONNECTORS:
> > +		if (!file_priv->atomic || !drm_core_check_feature(dev, DRIVER_ATOMIC))
> > +			return -EINVAL;
> Wondering how you can set the atomic cap without DRIVER_ATOMIC. :)

Caps can only be set one at a time. I was trying to cater for the cases
where userspace can set the WRITEBACK_CONNECTORS client cap before or
after setting the atomic cap.

> 
> That part could be dropped I think. We should probably WARN when trying to create a writeback connector without the DRIVER_ATOMIC cap set.

I could still keep the check for file_priv->atomic being set when
accepting the DRM_CLIENT_CAP_WRITEBACK_CONNECTORS and would not need a
warn.

Best regards,
Liviu

> > +		if (req->value > 1)
> > +			return -EINVAL;
> > +		file_priv->writeback_connectors = req->value;
> > +		break;
> >  	default:
> >  		return -EINVAL;
> >  	}
> > diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
> > index e5c653357024d..21e353bd3948e 100644
> > --- a/drivers/gpu/drm/drm_mode_config.c
> > +++ b/drivers/gpu/drm/drm_mode_config.c
> > @@ -145,6 +145,11 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
> >  	count = 0;
> >  	connector_id = u64_to_user_ptr(card_res->connector_id_ptr);
> >  	drm_for_each_connector_iter(connector, &conn_iter) {
> > +		/* only expose writeback connectors if userspace understands them */
> > +		if (!file_priv->writeback_connectors &&
> > +		    (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK))
> > +			continue;
> > +
> >  		if (drm_lease_held(file_priv, connector->base.id)) {
> >  			if (count < card_res->count_connectors &&
> >  			    put_user(connector->base.id, connector_id + count)) {
> > diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
> > index 5176c3797680c..2a09b3c8965c6 100644
> > --- a/include/drm/drm_file.h
> > +++ b/include/drm/drm_file.h
> > @@ -181,6 +181,13 @@ struct drm_file {
> >  	/** @atomic: True if client understands atomic properties. */
> >  	unsigned atomic:1;
> >  
> > +	/**
> > +	 * @writeback_connectors:
> > +	 *
> > +	 * True if client understands writeback connectors
> > +	 */
> > +	unsigned writeback_connectors:1;
> > +
> >  	/**
> >  	 * @is_master:
> >  	 *
> > diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> > index 6fdff5945c8a0..59f27ea928b42 100644
> > --- a/include/uapi/drm/drm.h
> > +++ b/include/uapi/drm/drm.h
> > @@ -680,6 +680,15 @@ struct drm_get_cap {
> >   */
> >  #define DRM_CLIENT_CAP_ATOMIC	3
> >  
> > +/**
> > + * DRM_CLIENT_CAP_WRITEBACK_CONNECTORS
> > + *
> > + * If set to 1, the DRM core will expose special connectors to be used for
> > + * writing back to memory the scene setup in the commit. Depends on client
> > + * also supporting DRM_CLIENT_CAP_ATOMIC
> > + */
> > +#define DRM_CLIENT_CAP_WRITEBACK_CONNECTORS	4
> > +
> >  /** DRM_IOCTL_SET_CLIENT_CAP ioctl argument type */
> >  struct drm_set_client_cap {
> >  	__u64 capability;
> 
> ~Maarten
> 

-- 
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