Den 05.08.2017 12.59, skrev Noralf Trønnes:
(I had to switch to Daniel's Intel address to get this sent)
Den 05.08.2017 00.19, skrev Ilia Mirkin:
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.
If drm_open() gets a ref on dev->dev and puts it in drm_release(),
won't that delay devm_* cleanup until userspace is done?
It seems plausible looking at the code:
void device_initialize(struct device *dev)
{
[...]
kobject_init(&dev->kobj, &device_ktype);
[...]
}
static struct kobj_type device_ktype = {
.release = device_release,
};
/**
* device_release - free device structure.
* @kobj: device's kobject.
*
* This is called once the reference count for the object
* reaches 0. We forward the call to the device's release
* method, which should handle actually freeing the structure.
*/
static void device_release(struct kobject *kobj)
{
[...]
devres_release_all(dev);
[...]
}
Last put call chain:
put_device() -> kobject_put() -> kref_put() -> kobject_release() ->
kobject_cleanup() -> device_release() -> devres_release_all()
But I haven't actually tried it, so I might be mistaken.
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