linux-kernel - Re: [PATCH v10 3/3] drm: writeback: Add client capability for exposing writeback connectors

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Message-ID: <20180613102605.GA8131@e107564-lin.cambridge.arm.com>
Date:   Wed, 13 Jun 2018 11:26:05 +0100
From:   Brian Starkey <brian.starkey@....com>
To:     Liviu Dudau <Liviu.Dudau@....com>
Cc:     Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        David Airlie <airlied@...ux.ie>,
        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>,
        Rob Clark <robdclark@...il.com>
Subject: Re: [PATCH v10 3/3] drm: writeback: Add client capability for
 exposing writeback connectors

Hi Liviu,

On Tue, Jun 12, 2018 at 02:52:33PM +0100, Liviu Dudau wrote:
>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.
>
>Changelog:
> - only accept the capability if the client has already set the
>DRM_CLIENT_CAP_ATOMIC one.
>
>Cc: Sean Paul <seanpaul@...omium.org>
>Cc: Brian Starkey <brian.starkey@....com>
>Signed-off-by: Liviu Dudau <liviu.dudau@....com>

LGTM,

Reviewed-by: Brian Starkey <brian.starkey@....com>

Thanks,
-Brian

>---
> 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 0d4cfb232576f..fe49fb0356b5a 100644
>--- a/drivers/gpu/drm/drm_ioctl.c
>+++ b/drivers/gpu/drm/drm_ioctl.c
>@@ -334,6 +334,13 @@ drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
> 			return -EINVAL;
> 		file_priv->aspect_ratio_allowed = req->value;
> 		break;
>+	case DRM_CLIENT_CAP_WRITEBACK_CONNECTORS:
>+		if (!file_priv->atomic)
>+			return -EINVAL;
>+		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 027ac16da3d15..26485acc51d79 100644
>--- a/include/drm/drm_file.h
>+++ b/include/drm/drm_file.h
>@@ -192,6 +192,13 @@ struct drm_file {
> 	 */
> 	unsigned aspect_ratio_allowed: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 9c660e1688abe..300f336633f28 100644
>--- a/include/uapi/drm/drm.h
>+++ b/include/uapi/drm/drm.h
>@@ -687,6 +687,15 @@ struct drm_get_cap {
>  */
> #define DRM_CLIENT_CAP_ASPECT_RATIO    4
>
>+/**
>+ * 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	5
>+
> /** DRM_IOCTL_SET_CLIENT_CAP ioctl argument type */
> struct drm_set_client_cap {
> 	__u64 capability;
>-- 
>2.17.1
>