Re: [Nouveau] [PATCH v3 03/20] drm/dp: Move i2c init to drm_dp_aux_init, add __must_check and fini

From: Thierry Reding <treding@nvidia.com>
To: Lyude Paul <lyude@redhat.com>
Cc: "Neil Armstrong" <narmstrong@baylibre.com>,
	"David Airlie" <airlied@linux.ie>,
	nouveau@lists.freedesktop.org, "Guido Günther" <agx@sigxcpu.org>,
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Subject: Re: [Nouveau] [PATCH v3 03/20] drm/dp: Move i2c init to drm_dp_aux_init, add __must_check and fini
Date: Fri, 23 Apr 2021 14:39:32 +0200	[thread overview]
Message-ID: <YILABCrcMb5MksxD@orome.fritz.box> (raw)
In-Reply-To: <17aa145e4cfa3d8852f7411067c5c37bff771b16.camel@redhat.com>

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On Fri, Apr 23, 2021 at 12:11:06AM -0400, Lyude Paul wrote:
> On Thu, 2021-04-22 at 18:33 -0400, Lyude Paul wrote:
> > OK - talked with Ville a bit on this and did some of my own research, I
> > actually think that moving i2c to drm_dp_aux_init() is the right decision
> > for
> > the time being. The reasoning behind this being that as shown by my previous
> > work of fixing drivers that call drm_dp_aux_register() too early - it seems
> > like there's already been drivers that have been working just fine with
> > setting up the i2c device before DRM registration. 
> > 
> > In the future, it'd probably be better if we can split up i2c_add_adapter()
> > into an init and register function - but we'll have to talk with the i2c
> > maintainers to see if this is acceptable w/ them
> 
> Actually - I think adding the ability to refcount dp aux adapters might be a
> better solution so I'm going to try that!

I'm curious: how is a DP AUX adapter reference count going to solve the
issue of potentially registering devices too early (i.e. before the DRM
is registered)?

Is it because registering too early could cause a reference count
problem if somebody get a hold of the DP AUX adapter before the parent
DRM device is around?

Thierry

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