Re: [PATCH v3 8/9] dt-bindings: media: nxp,imx8mq-vpu: Update bindings

Hi Rob,

On Tue, 2021-02-23 at 08:31 -0600, Rob Herring wrote:

On Tue, Feb 23, 2021 at 2:04 AM Benjamin Gaignard
[off-list ref] wrote:

quoted

Le 23/02/2021 à 01:34, Rob Herring a écrit :

quoted

On Mon, Feb 22, 2021 at 01:24:05PM +0100, Benjamin Gaignard wrote:

quoted

The current bindings seem to make the assumption that the
two VPUs hardware blocks (G1 and G2) are only one set of
registers.
After implementing the VPU reset driver and G2 decoder driver
it shows that all the VPUs are independent and don't need to
know about the registers of the other blocks.
Remove from the bindings the need to set all blocks register
but keep reg-names property because removing it from the driver
may affect other variants.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
---
version 2:
- be more verbose about why I change the bindings
Keep in mind that series comes after: https://www.spinics.net/lists/arm-kernel/msg875766.html
without that review and ack it won't work

Better, but you've still mentioned nothing about breaking compatibility.
Why is that okay?

Indeed, the commit description should be clearer about breaking compatibility.

quoted

Because this reg-names wasn't used before for this variant so remove it won't change anything.

It is the reset changes in the driver that break. The driver
previously got the 'ctrl' registers whether it went by name or index,
right? With an old DTB and a kernel with the changes (and vice-versa),
you'll have nothing to handle the VPU resets because the VPU reset
node doesn't exist. It could work if the default state is not held in
reset.

At least the removal of 'ctrl' registers belongs in the reset changes series.

Considering that FFMPEG patches that are required to support this driver
are still floating around, and GStreamer's implementation is also still
a bit under discussion, we are certain there aren't many upstreams users
(leaving ChromiumOS aside which mostly care for Rockchip variants).

So, given the driver is in staging, and that there aren't users of the
i.MX8MQ G1 variant just yet, I think we are safe breaking the compatibility
(and I'm not taking it lightly).

It would be important to detect an old devicetree and do some pr_warn about
the driver not supporting it.

Thanks,
Ezequiel


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