Re: [PATCH 2/2] drm/bridge: ti-sn65dsi83: protect device resources on unplug

[Maxime Ripard <mripard@kernel.org>]

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On Wed, Aug 20, 2025 at 01:13:02PM +0200, Luca Ceresoli wrote:
> Hello Maxime,
> 
> On Tue, 19 Aug 2025 14:29:32 +0200
> Maxime Ripard <mripard@kernel.org> wrote:
> 
> > > @@ -1005,7 +1041,24 @@ static void sn65dsi83_remove(struct i2c_client *client)
> > >  {
> > >  	struct sn65dsi83 *ctx = i2c_get_clientdata(client);
> > >  
> > > +	drm_bridge_unplug(&ctx->bridge);
> > >  	drm_bridge_remove(&ctx->bridge);  
> > 
> > Shouldn't we merge drm_bridge_unplug with the release part of
> > devm_drm_bridge_alloc?
> 
> I'm not sure I got what you are suggesting here, sorry.
> 
> Do you mean that __devm_drm_bridge_alloc() should add a devres action
> to call drm_bridge_unplug(), so the unplug is called implicitly and
> does not need to be called explicitly by all drivers?

Yes

> If that's what you mean, I don't think that would work. Unless I'm
> missing something, devres actions are always invoked just after the
> driver .remove callback.

Yes, they are called in reverse order of registration, after remove.

> But we need to call drm_bridge_unplug() at the beginning (or just
> before) .remove, at least for drivers that need to do something in
> .remove that cannot be done by devm.
> 
> In pseudocode:
> 
> mybridge_remove()
> {
>   drm_bridge_unplug(); <-- explicit call as in my patch
>   xyz_disable();
>   drm_bridge_unplug(); <-- implicitly done by devres
> }
> 
> We want xyz_disable() to be done after drm_bridge_unplug(), so other
> code paths using drm_bridge_enter/exit() won't mess with xyz.

It's not clear to me why doing it before xyz_disable() is important
here? If anything, it would prevent from disabling the hardware for
example, even though you still have your memory mapping, clocks, power
domains, regulators, etc. to properly disable it.

You're still correct that it's a bad idea though because we want to do
it before we start freeing all those, so it needs to execute as the
before the devm actions ...

> devres actions cannot be added to be executed _before_ .remove, AFAIK.

... and we can't do that either.

Maxime

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