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Message-ID: <20250314091120.366b5fd7@booty>
Date: Fri, 14 Mar 2025 09:11:20 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, Jagan
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linux-arm-kernel@...ts.infradead.org, Paul Kocialkowski
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Subject: Re: [PATCH v6 14/26] drm/bridge: add support for refcounted DRM
bridges
Hello Maxime,
On Thu, 13 Mar 2025 19:07:17 +0100
Maxime Ripard <mripard@...nel.org> wrote:
> On Thu, Mar 13, 2025 at 12:56:56PM +0100, Luca Ceresoli wrote:
> > Hello Maxime,
> >
> > On Fri, 7 Feb 2025 12:47:51 +0100
> > Maxime Ripard <mripard@...nel.org> wrote:
> > > On Thu, Feb 06, 2025 at 07:14:29PM +0100, Luca Ceresoli wrote:
> > > > DRM bridges are currently considered as a fixed element of a DRM card, and
> > > > thus their lifetime is assumed to extend for as long as the card
> > > > exists. New use cases, such as hot-pluggable hardware with video bridges,
> > > > require DRM bridges to be added and removed to a DRM card without tearing
> > > > the card down. This is possible for connectors already (used by DP MST), so
> > > > add this possibility to DRM bridges as well.
> > > >
> > > > Implementation is based on drm_connector_init() as far as it makes sense,
> > > > and differs when it doesn't. A difference is that bridges are not exposed
> > > > to userspace, hence struct drm_bridge does not embed a struct
> > > > drm_mode_object which would provide the refcount. Instead we add to struct
> > > > drm_bridge a refcount field (we don't need other struct drm_mode_object
> > > > fields here) and instead of using the drm_mode_object_*() functions we
> > > > reimplement from those functions the few lines that drm_bridge needs for
> > > > refcounting.
> > > >
> > > > Also add a new devm_drm_bridge_alloc() macro to allocate a new refcounted
> > > > bridge.
> > > >
> > > > Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > >
> > > So, a couple of general comments:
> > >
> > > - I've said it a couple of times already, but I really think you're
> > > making it harder than necessary for you here. This (and only this!)
> > > should be the very first series you should be pushing. The rest can
> > > only ever work if that work goes through, and it's already hard enough
> > > as it is. So, split that patch into a series of its own, get that
> > > merged, and then we will be able to deal with panels conversion and
> > > whatever. That's even more true with panels since there's ongoing work
> > > that will make it easier for you too. So the best thing here is
> > > probably to wait.
> > >
> > > - This patch really needs to be split into several patches, something
> > > along the lines of:
> > >
> > > + Creating devm_drm_bridge_alloc()
> > > + Adding refcounting
> > > + Taking the references in all the needed places
> > > + Converting a bunch of drivers
> >
> > After reading Anusha's "[PATCH RFC 0/2] drm/panel: Refcounted panel
> > allocation" [0] I think I need a clarification about the 4 steps you had
> > outlined in the above quoted text. Are you suggesting those are four
> > _series_, and you'd want to see a series only creating
> > devm_drm_bridge_alloc() as a first step, similarly to Anusha's work?
> >
> > That was not my understanding so far, and so I've been working on a
> > series containing all 4 items, and it's growing very long due to item 3
> > needing to touch many dozen drivers which need to put a bridge (many
> > are identical oneliner patches though).
>
> I believe I've clarified it already in Anusha's series, but I think a
Yes, you have...
> reasonable series for *early* work would be the bullet points 1, 2, a
> bit of 3 and a bit of 4.
...but thanks for the extra clarification.
Luca
--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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