Re: [PATCH 00/24] device link, bridge supplier <-> drm device

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Peter Rosin <peda@axentia.se>
Cc: Martyn Welch <martyn.welch@collabora.co.uk>,
	David Airlie <airlied@linux.ie>,
	dri-devel@lists.freedesktop.org, linux-samsung-soc@vger.kern,
	Kyungmin Park <kyungmin.park@samsung.com>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Kukjin Kim <kgene@kernel.org>,
	Peter Senna Tschudin <peter.senna@collabora.com>,
	Martin Donnelly <martin.donnelly@ge.com>,
	linux-arm-msm@vger.kernel.org, Jyri Sarha <jsarha@ti.com>,
	el.org@freedesktop.org, Matthias Brugger <matthias.bgg@gmail.com>,
	Vincent Abriou <vincent.abriou@st.com>,
	linux-arm-kernel@lists.infradead.org,
	Seung-Woo Kim <sw0312.kim@samsung.com>,
	linux-kernel@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
	linux-mediatek@lists.infradead.org,
	freedreno@lists.freedesktop.org
Subject: Re: [PATCH 00/24] device link, bridge supplier <-> drm device
Date: Fri, 27 Apr 2018 02:18:27 +0300	[thread overview]
Message-ID: <3483427.EaMxDYJt8U@avalon> (raw)
In-Reply-To: <8a9fcd8c-962d-1acc-c2ba-74a3d8f59590@axentia.se>

Hi Peter,

On Friday, 27 April 2018 02:09:14 EEST Peter Rosin wrote:
> On 2018-04-27 00:40, Laurent Pinchart wrote:
> > On Friday, 27 April 2018 01:31:15 EEST Peter Rosin wrote:
> >> Hi!
> >> 
> >> It was noted by Russel King [1] that bridges (not using components)
> >> might disappear unexpectedly if the owner of the bridge was unbound.
> >> Jyri Sarha had previously noted the same thing with panels [2]. Jyri
> >> came up with using device links to resolve the panel issue, which
> >> was also my (independent) reaction to the note from Russel.
> >> 
> >> This series builds up to the addition of that link in the last
> >> patch, but in my opinion the other 23 patches do have merit on their
> >> own.
> >> 
> >> The last patch needs testing, while the others look trivial. That
> >> said, I might have missed some subtlety.
> > 
> > I don't think this is the way to go. We have a real lifetime management
> > problem with bridges, and device links are just trying to hide the problem
> > under the carpet. They will further corner us by making a real fix much
> > more difficult to implement. I'll try to comment further in the next few
> > days on what I think a better solution would be, but in a nutshell I
> > believe that drm_bridge objects need to be refcounted, with a .release()
> > operation to free the bridge resources when the reference count drops to
> > zero. This shouldn't be difficult to implement and I'm willing to help.
> 
> Ok, sp 24/24 is dead, and maybe 23/24 too.

Not necessarily, maybe I'll get proven wrong :-) Let's discuss, but I first 
need some sleep.

> But how do you feel about dropping .of_node in favour of .owner? That gets
> rid of ugly #ifdefs...

I'll review that part and reply, I have nothing against it on principle at the 
moment. The more generic the code is, the better in my opinion. We just need 
to make sure that the OF node we're interested in will always be .owner-
>of_node in all cases.

> I also have the nagging feeling that .driver_private serves very little real
> purpose if there is a .owner so that you can do
> 
> 	dev_get_drvdata(bridge->owner)
> 
> for the cases where the container_of macro is not appropriate.

I'll review that too, it's a good point.

-- 
Regards,

Laurent Pinchart

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