Re: [PATCH v5 2/6] drm/bridge: Add a devm_ allocator for panel bridge.

From: Ilia Mirkin
Date: Fri Aug 04 2017 - 18:20:18 EST

On Fri, Aug 4, 2017 at 4:43 PM, Eric Anholt <eric@xxxxxxxxxx> wrote:
> Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> writes:
>> Hi Eric,
>> (CC'ing Daniel)
>> Thank you for the patch.
>> On Tuesday 18 Jul 2017 14:05:06 Eric Anholt wrote:
>>> This will let drivers reduce the error cleanup they need, in
>>> particular the "is_panel_bridge" flag.
>>> v2: Slight cleanup of remove function by Andrzej
>> I just want to point out that, in the context of Daniel's work on hot-unplug,
>> 90% of the devm_* allocations are wrong and will get in the way. All DRM core
>> objects that are accessible one way or another from userspace will need to be
>> properly reference-counted and freed only when the last reference disappears,
>> which could be well after the corresponding device is removed. I believe this
>> could be one such objects :-/
> Sure, if you're hotplugging, your life is pain. For non-hotpluggable
> devices, like our SOC platform devices (current panel-bridge consumers),
> this still seems like an excellent simplification of memory management.

At that point you may as well make your module non-unloadable, and
return failure when trying to remove a device from management by the
driver (whatever the opposite of "probe" is, I forget). Hotplugging
doesn't only happen when physically removing, it can happen for all
kinds of reasons... and userspace may still hold references in some of
those cases.