Re: [PATCH v11 2/3] drm/bridge: imx: Add i.MX93 parallel display format configuration support

Marco Felsch
2026-03-11T19:45:57Z

Hi Liu, Luca,

sorry for the delayed response, I was at the EW26.

On 26-03-10, Luca Ceresoli wrote:
> Hi Liu, Marco,
>
> On Tue Mar 10, 2026 at 3:57 AM CET, Liu Ying wrote:
> > Hi Marco, Luca,
> >
> > On Tue, Mar 03, 2026 at 11:34:27AM +0100, Marco Felsch wrote:
> >
> > [...]
> >
> >> + next_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 1, 0);
> >> + if (IS_ERR(next_bridge))
> >> + return dev_err_probe(dev, PTR_ERR(next_bridge),
> >> + "failed to get next bridge\n");
> >> + pdfc->dev = dev;
> >> + pdfc->bridge.of_node = dev->of_node;
> >> + pdfc->bridge.type = DRM_MODE_CONNECTOR_DPI;
> >> + pdfc->bridge.next_bridge = next_bridge;
> >
> > When I was reviewing another patch[1], I was aware of the necessity of
> > calling drm_bridge_get() for next_bridge to balance the next bridge's
> > refcount put from __drm_bridge_free() for this bridge. I'd be good if
> > Luca may confirm this is correct. Sorry for bringing this up late.
>
> Indeed you have a good point.

At which stage did you faced this issue? During driver probe, because of
EPROBE_DEFER?

That's the reason for having the local next_bridge variable since I
faced with the same issue. In other words this driver is correct and
it's on purpose to not assign it directly. Albeit I could/should have
added a comment.

> After re-checking devm_drm_of_get_bridge(), as I wrote on the other thread
> you pointed to, you should call drm_bridge_get():
>
> - pdfc->bridge.next_bridge = next_bridge;
> + pdfc->bridge.next_bridge = drm_bridge_get(next_bridge);
>
> Marco, you can keep my R-by if you resend with just this change.
>
> Sorry about the confusion here.
>
> As mention on the other thread, devm_drm_of_get_bridge() is unable to
> support bridge hotplug. So it should be deprecated, but as of now there is
> no alternative.

Sorry I need a bit more context. What's the issue? How can I trigger the
issue? Why is bridge hotplug required at this stage? Why is only this
bridge affecte by the hotplug issue?

Regards,
Marco

>
> Luca
>
> --
> Luca Ceresoli, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com
>

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