Re: [PATCH] Revert "[media] v4l: async: make v4l2 coexist with devicetree nodes in a dt overlay"

[Javi Merino <javi.merino@kernel.org>]

On Thu, Jul 20, 2017 at 05:06:22PM -0500, Rob Herring wrote:
> This reverts commit d2180e0cf77dc7a7049671d5d57dfa0a228f83c1.
> 
> The commit was flawed in that if the device_node pointers are different,
> then in fact a different device is present and the device node could be
> different in ways other than full_name.
> 
> As Frank Rowand explained:
> 
> "When an overlay (1) is removed, all uses and references to the nodes and
> properties in that overlay are no longer valid.  Any driver that uses any
> information from the overlay _must_ stop using any data from the overlay.
> Any driver that is bound to a new node in the overlay _must_ unbind.  Any
> driver that became bound to a pre-existing node that was modified by the
> overlay (became bound after the overlay was applied) _must_ adjust itself
> to account for any changes to that node when the overlay is removed.  One
> way to do this is to unbind when notified that the overlay is about to
> be removed, then to re-bind after the overlay is completely removed.
> 
> If an overlay (2) is subsequently applied, a node with the same
> full_name as from overlay (1) may exist.  There is no guarantee
> that overlay (1) and overlay (2) are the same overlay, even if
> that node has the same full_name in both cases."
> 
> Also, there's not sufficient overlay support in mainline to actually
> remove and re-apply an overlay to hit this condition as overlays can
> only be applied from in kernel APIs.
> 
> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
> Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
> Cc: Javi Merino <javi.merino@kernel.org>
> Cc: Javier Martinez Canillas <javier@osg.samsung.com>
> Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>
> Cc: Frank Rowand <frowand.list@gmail.com>
> Signed-off-by: Rob Herring <robh@kernel.org>

I've been trying to reproduce the original issues that I had for a
couple of hours and I am not able to any more, so I can't object to
the patch.  The explanation from Frank Rowand is sound so:

Acked-by: Javi Merino <javi.merino@kernel.org>

> ---
> Mauro, please apply this for 4.13. It could be marked for stable, too, 
> but it's not going to apply cleanly with the fwnode changes.
> 
> Rob
> 
>  drivers/media/v4l2-core/v4l2-async.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)