On Thu, Mar 04, 2021 at 03:05:32PM +0100, Nicolas Saenz Julienne wrote:

Hi Greg.

On Thu, 2021-03-04 at 14:46 +0100, Greg KH wrote:

quoted

On Wed, Mar 03, 2021 at 03:33:12PM +0800, Jing Xiangfeng wrote:

quoted

Using two distinct DMA zones turned out to be problematic. Here's an
attempt go back to a saner default.

What problem does this solve?  How does this fit into the stable kernel
rules?

We changed the way we setup memory zones in arm64 in order to cater for
Raspberry Pi 4's weird DMA constraints: ZONE_DMA spans the lower 1GB of memory
and ZONE_DMA32 the rest of the 32bit address space. Since you can't allocate
memory that crosses zone boundaries, this broke crashkernel allocations on big
machines. This series fixes all this by parsing the HW description and checking
for DMA constrained buses. When not found, the unnecessary zone creation is
skipped.

What kernel/commit caused this "breakage"?

thanks,

greg k-h