From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux admin Subject: Re: [PATCHv8 2/2] drm: tda998x: set the connector info Date: Thu, 17 Oct 2019 10:44:13 +0100 Message-ID: <20191017094413.GB25745@shell.armlinux.org.uk> References: <20191016133916.21475-1-hverkuil-cisco@xs4all.nl> <20191016133916.21475-3-hverkuil-cisco@xs4all.nl> <20191016162232.GY25745@shell.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:3201:214:fdff:fe10:1be6]) by gabe.freedesktop.org (Postfix) with ESMTPS id 79A9B6EA30 for ; Thu, 17 Oct 2019 09:44:26 +0000 (UTC) Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Dariusz Marcinkiewicz Cc: Hans Verkuil , Laurent Pinchart , dri-devel@lists.freedesktop.org, 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ARM Linux admin To: Dariusz Marcinkiewicz Cc: Hans Verkuil , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, Daniel Vetter , Laurent Pinchart Subject: Re: [PATCHv8 2/2] drm: tda998x: set the connector info Message-ID: <20191017094413.GB25745@shell.armlinux.org.uk> References: <20191016133916.21475-1-hverkuil-cisco@xs4all.nl> <20191016133916.21475-3-hverkuil-cisco@xs4all.nl> <20191016162232.GY25745@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Thu, Oct 17, 2019 at 11:26:38AM +0200, Dariusz Marcinkiewicz wrote: > Hi Russel. > > On Wed, Oct 16, 2019 at 6:22 PM Russell King - ARM Linux admin > wrote: > > > ... > > > --- a/drivers/gpu/drm/i2c/tda998x_drv.c > > > +++ b/drivers/gpu/drm/i2c/tda998x_drv.c > > > @@ -1337,6 +1337,8 @@ static int tda998x_connector_init(struct tda998x_priv *priv, > > > struct drm_device *drm) > > > { > > > struct drm_connector *connector = &priv->connector; > > > + struct cec_connector_info conn_info; > > > + struct cec_notifier *notifier; > > > int ret; > > > > > > connector->interlace_allowed = 1; > > > @@ -1353,6 +1355,17 @@ static int tda998x_connector_init(struct tda998x_priv *priv, > > > if (ret) > > > return ret; > > > > > > + cec_fill_conn_info_from_drm(&conn_info, connector); > > > + > > > + notifier = cec_notifier_conn_register(priv->cec_glue.parent, > > > + NULL, &conn_info); > > > + if (!notifier) > > > + return -ENOMEM; > > > + > > > + mutex_lock(&priv->cec_notify_mutex); > > > + priv->cec_notify = notifier; > > > + mutex_unlock(&priv->cec_notify_mutex); > > > > As per my previous comments, this is a single-copy atomic operation. > > Either priv->cec_notify is set or it isn't; there is no intermediate > > value. It can't be set to a value until cec_notifier_conn_register() > > has completed. So the lock doesn't help. > > > .... > > > + > > > drm_connector_attach_encoder(&priv->connector, > > > priv->bridge.encoder); > > > > > > @@ -1372,6 +1385,11 @@ static void tda998x_bridge_detach(struct drm_bridge *bridge) > ... > > > + mutex_lock(&priv->cec_notify_mutex); > > > + cec_notifier_conn_unregister(priv->cec_notify); > > > + priv->cec_notify = NULL; > > > + mutex_unlock(&priv->cec_notify_mutex); > > > > This is the only case where the lock makes sense - to ensure that any > > of the cec_notifier_set_phys_addr*() functions aren't called > > concurrently with it. However, there's no locking around the instance > > in tda998x_connector_get_modes(), so have you ensured that that > > function can't be called concurrently? > > > I assumed that tda998x_connector_get_modes does not need to be > synchronized as it belongs to the connector that gets cleaned up here. > But, on a closer look, I don't think that this assumption necessarily > holds. > > If this patch is to be merged, I can send an update that: > - strips locking from tda998x_connector_init, > - in tda998x_connector_get_modes calls cec_notifier* with the lock held. Okay, I'd suggest a comment in the code describing precisely what the lock is doing would be a good idea, as it may not be obvious in the future. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up