linux-kernel - Re: [PATCH v2 26/26] drm/bridge: establish a link between the bridge supplier and consumer

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Message-ID: <73fa1ca3-28e4-96c5-1fc6-23e9c0cebb49@axentia.se>
Date:   Mon, 14 May 2018 22:40:58 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Andrzej Hajda <a.hajda@...sung.com>, linux-kernel@...r.kernel.org,
        Archit Taneja <architt@...eaurora.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Peter Senna Tschudin <peter.senna@...labora.com>,
        Martin Donnelly <martin.donnelly@...com>,
        Martyn Welch <martyn.welch@...labora.co.uk>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        CK Hu <ck.hu@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Rob Clark <robdclark@...il.com>,
        Sandy Huang <hjc@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Vincent Abriou <vincent.abriou@...com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, Jyri Sarha <jsarha@...com>
Subject: Re: [PATCH v2 26/26] drm/bridge: establish a link between the bridge
 supplier and consumer

On 2018-05-14 18:28, Daniel Vetter wrote:
> On Fri, May 11, 2018 at 09:37:47AM +0200, Peter Rosin wrote:
>> On 2018-05-10 10:10, Andrzej Hajda wrote:
>>> On 04.05.2018 15:52, Peter Rosin wrote:
>>>> If the bridge supplier is unbound, this will bring the bridge consumer
>>>> down along with the bridge. Thus, there will no longer linger any
>>>> dangling pointers from the bridge consumer (the drm_device) to some
>>>> non-existent bridge supplier.
>>>>
>>>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>>>> ---
>>>>  drivers/gpu/drm/drm_bridge.c | 18 ++++++++++++++++++
>>>>  include/drm/drm_bridge.h     |  2 ++
>>>>  2 files changed, 20 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
>>>> index 78d186b6831b..0259f0a3ff27 100644
>>>> --- a/drivers/gpu/drm/drm_bridge.c
>>>> +++ b/drivers/gpu/drm/drm_bridge.c
>>>> @@ -26,6 +26,7 @@
>>>>  #include <linux/mutex.h>
>>>>  
>>>>  #include <drm/drm_bridge.h>
>>>> +#include <drm/drm_device.h>
>>>>  #include <drm/drm_encoder.h>
>>>>  
>>>>  #include "drm_crtc_internal.h"
>>>> @@ -127,12 +128,25 @@ int drm_bridge_attach(struct drm_encoder *encoder, struct drm_bridge *bridge,
>>>>  	if (bridge->dev)
>>>>  		return -EBUSY;
>>>>  
>>>> +	if (encoder->dev->dev != bridge->odev) {
>>>
>>> I wonder why device_link_add does not handle this case (self dependency)
>>> silently as noop, as it seems to be a correct behavior.
>>
>> It's kind-of a silly corner-case though, so perfectly understandable
>> that it isn't handled.
>>
>>>> +		bridge->link = device_link_add(encoder->dev->dev,
>>>> +					       bridge->odev, 0);
>>>> +		if (!bridge->link) {
>>>> +			dev_err(bridge->odev, "failed to link bridge to %s\n",
>>>> +				dev_name(encoder->dev->dev));
>>>> +			return -EINVAL;
>>>> +		}
>>>> +	}
>>>> +
>>>>  	bridge->dev = encoder->dev;
>>>>  	bridge->encoder = encoder;
>>>>  
>>>>  	if (bridge->funcs->attach) {
>>>>  		ret = bridge->funcs->attach(bridge);
>>>>  		if (ret < 0) {
>>>> +			if (bridge->link)
>>>> +				device_link_del(bridge->link);
>>>> +			bridge->link = NULL;
>>>>  			bridge->dev = NULL;
>>>>  			bridge->encoder = NULL;
>>>>  			return ret;
>>>> @@ -159,6 +173,10 @@ void drm_bridge_detach(struct drm_bridge *bridge)
>>>>  	if (bridge->funcs->detach)
>>>>  		bridge->funcs->detach(bridge);
>>>>  
>>>> +	if (bridge->link)
>>>> +		device_link_del(bridge->link);
>>>> +	bridge->link = NULL;
>>>> +
>>>>  	bridge->dev = NULL;
>>>>  }
>>>>  
>>>> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
>>>> index b656e505d11e..804189c63a4c 100644
>>>> --- a/include/drm/drm_bridge.h
>>>> +++ b/include/drm/drm_bridge.h
>>>> @@ -261,6 +261,7 @@ struct drm_bridge_timings {
>>>>   * @list: to keep track of all added bridges
>>>>   * @timings: the timing specification for the bridge, if any (may
>>>>   * be NULL)
>>>> + * @link: drm consumer <-> bridge supplier
>>>
>>> Nitpick: "<->" suggests symmetry, maybe "device link from drm consumer
>>> to the bridge" would be better.
>>
>> I meant "<->" to indicate that the link is bidirectional, not that the
>> relationship is in any way symmetric. I wasn't aware of any implication
>> of a symmetric relationship when using "<->", do you have a reference?
>> But I guess the different arrow notations in math are somewhat overloaded
>> and that someone at some point must have used "<->" to indicate a
>> symmetric relationship...
> 
> Yeah I agree with Andrzej here, for me <-> implies a symmetric
> relationship. Spelling it out like Andrzej suggested sounds like the
> better idea.
> -Daniel

Ok, I guess that means I have to do a v3 after all. Or can this
trivial documentation update be done by the committer? I hate to
spam everyone with another volley...

Or perhaps I should squash patches 2-23 that are all rather similar
and mechanic? I separated them to allow for easier review from
individual driver maintainers, but that didn't seem to happen
anyway...

Cheers,
Peter

> 
>>
>>> Anyway:
>>> Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
>>
>> Thanks!
>>
>> Cheers,
>> Peter
>>
>>>  --
>>> Regards
>>> Andrzej
>>>
>>>>   * @funcs: control functions
>>>>   * @driver_private: pointer to the bridge driver's internal context
>>>>   */
>>>> @@ -271,6 +272,7 @@ struct drm_bridge {
>>>>  	struct drm_bridge *next;
>>>>  	struct list_head list;
>>>>  	const struct drm_bridge_timings *timings;
>>>> +	struct device_link *link;
>>>>  
>>>>  	const struct drm_bridge_funcs *funcs;
>>>>  	void *driver_private;
>>>
>>>
>>
>