Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752591AbbKPQXR (ORCPT ); Mon, 16 Nov 2015 11:23:17 -0500 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:60036 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751824AbbKPQXL (ORCPT ); Mon, 16 Nov 2015 11:23:11 -0500 Date: Mon, 16 Nov 2015 16:22:41 +0000 From: Russell King - ARM Linux To: Liviu Dudau Cc: Mark Yao , Heiko Stuebner , Philipp Zabel , Daniel Vetter , David Airlie , Eric Anholt , linux-rockchip , LAKML , dri-devel , LKML Subject: Re: [PATCH 1/2] drm: Improve drm_of_component_probe() to correctly handle ports and remote ports. Message-ID: <20151116162241.GN8644@n2100.arm.linux.org.uk> References: <1447685093-26129-1-git-send-email-Liviu.Dudau@arm.com> <1447685093-26129-2-git-send-email-Liviu.Dudau@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1447685093-26129-2-git-send-email-Liviu.Dudau@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4284 Lines: 107 On Mon, Nov 16, 2015 at 02:44:52PM +0000, Liviu Dudau wrote: > Rockchip DRM driver cannot use the same compare_of() function to match > ports and remote ports (aka encoders) as their OF sub-trees look different. > Add a second compare function to be used when encoders are added to the > component framework and patch the existing users of the function > accordingly. > > Signed-off-by: Liviu Dudau > --- > drivers/gpu/drm/armada/armada_drv.c | 3 ++- > drivers/gpu/drm/drm_of.c | 23 ++++++++++++++++++----- > drivers/gpu/drm/imx/imx-drm-core.c | 3 ++- > include/drm/drm_of.h | 6 ++++-- > 4 files changed, 26 insertions(+), 9 deletions(-) > > diff --git a/drivers/gpu/drm/armada/armada_drv.c b/drivers/gpu/drm/armada/armada_drv.c > index 77ab93d..3a2a929 100644 > --- a/drivers/gpu/drm/armada/armada_drv.c > +++ b/drivers/gpu/drm/armada/armada_drv.c > @@ -274,7 +274,8 @@ static int armada_drm_probe(struct platform_device *pdev) > struct device *dev = &pdev->dev; > int ret; > > - ret = drm_of_component_probe(dev, compare_dev_name, &armada_master_ops); > + ret = drm_of_component_probe(dev, compare_dev_name, compare_dev_name, > + &armada_master_ops); > if (ret != -EINVAL) > return ret; > > diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c > index 493c05c..58fafd7 100644 > --- a/drivers/gpu/drm/drm_of.c > +++ b/drivers/gpu/drm/drm_of.c > @@ -77,7 +77,8 @@ EXPORT_SYMBOL(drm_of_find_possible_crtcs); > * Returns zero if successful, or one of the standard error codes if it fails. > */ > int drm_of_component_probe(struct device *dev, > - int (*compare_of)(struct device *, void *), > + int (*compare_port)(struct device *, void *), > + int (*compare_encoder)(struct device *, void *), > const struct component_master_ops *m_ops) > { > struct device_node *ep, *port, *remote; > @@ -101,8 +102,14 @@ int drm_of_component_probe(struct device *dev, > continue; > } > > - component_match_add(dev, &match, compare_of, port); > - of_node_put(port); > + component_match_add(dev, &match, compare_port, port); > + /* > + * component_match_add keeps a reference to the port > + * variable but does not do proper reference counting, > + * so we cannot release the reference here. If that > + * gets fixed, the following line should be uncommented > + */ > + /* of_node_put(port); */ Even if it is fixed, this line should _never_ be uncommented. This is totally the wrong place to drop the reference. > } > > if (i == 0) { > @@ -140,8 +147,14 @@ int drm_of_component_probe(struct device *dev, > continue; > } > > - component_match_add(dev, &match, compare_of, remote); > - of_node_put(remote); > + component_match_add(dev, &match, compare_encoder, remote); > + /* > + * component_match_add keeps a reference to the port > + * variable but does not do proper reference counting, > + * so we cannot release the reference here. If that > + * gets fixed, the following line should be uncommented > + */ > + /* of_node_put(remote); */ Ditto. The component helper retains a reference (by pointer value) to the 'port' or 'remote', which is then subsequently passed into the supplied 'compare_encoder' or 'compare_port' method. If you drop the reference after adding the match, then that pointer can go away and be re-used for something else - and that means it's totally useless to the compare functions, since the memory pointed to by it may not contain an device_node struct anymore. So, it _never_ makes sense to drop the reference at this point. Where it does make sense is when the array of matches is destroyed. For that, we'd need to add a callback to the master ops struct so that the master driver can properly release these pointers. I'd keep most of the big comments though (up to "... varable") to explain why we don't drop the reference. -- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/