I thought downstream kept kernels and DTs in sync, so the dts could be
fixed?

For Pixel the kernel and DT are in sync, but I'm not sure about other devices.
The problem in general though is now everyone would need to do a special
coordination when updating to the newer LTS version to make sure their kernel
matches the new DT.

On 02/26/2025, Rob Herring wrote:

On Wed, Feb 26, 2025 at 2:31 PM Zijun Hu [off-list ref] wrote:

quoted

On 2025/2/27 03:45, Rob Herring wrote:

quoted

quoted

Right, I think it's already backported to the LTS kernels, but if it breaks any
in-tree users then we'd have to revert it. I just like Rob's idea to instead
change the spec for obvious reasons 🙂

While if it is downstream, it doesn't exist, I'm reverting this for now.

perhaps, it is better for us to slow down here.

1) This change does not break any upstream code.
   is there downstream code which is publicly visible and is broken by
   this change ?

We don't know that unless you tested every dts file. We only know that
no one has reported an issue yet.

Even if we did test everything, there are DT's that aren't in the
kernel tree. It's not like this downstream DT is using some
undocumented binding or questionable things. It's a standard binding.

Every time this code is touched, it breaks. This is not even the only
breakage right now[1].

You can find the Pixel 6/7/8/9 device trees on android.googlesource.com.
You can see for zuma based devices (Pixel 9 for example) they have this [1]:

  &reserved_memory {
        #address-cells = <2>;
        #size-cells = <1>;
        vstream: vstream {
                compatible = "shared-dma-pool";
                reusable;
                size = <0x4800000>;
                alignment = <0x0 0x00010000>;
                alloc-ranges = <0x9 0x80000000 0x80000000>,
                               <0x9 0x00000000 0x80000000>,
                               <0x8 0x80000000 0x80000000>,
                               <0x0 0x80000000 0x80000000>;
        };

I understand this code is downstream, but as a general principle we shouldn't
break backwards compatibilty.

Thanks,
Will

[1] https://android.googlesource.com/kernel/devices/google/zuma/+/refs/heads/android-gs-shusky-6.1-android16-dp/dts/gs101-dma-heap.dtsi#147

quoted

2) IMO, the spec may be right.
   The type of size is enough to express any alignment wanted.
   For several kernel allocators. type of 'alignment' should be the type
   of 'size', NOT the type of 'address'

As I said previously, it can be argued either way.

Rob

[1] https://lore.kernel.org/all/20250226115044.zw44p5dxlhy5eoni@pengutronix.de/ (local)