Messages in this thread | | | Date | Tue, 24 Mar 2020 17:41:35 +0000 | From | Catalin Marinas <> | Subject | Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable without EXPERT |
| |
On Tue, Mar 10, 2020 at 08:48:46PM +0800, peng.fan@nxp.com wrote: > From: Peng Fan <peng.fan@nxp.com> > > commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32") > enables both ZONE_DMA and ZONE_DMA32. The lower 1GB memory > will be occupied by ZONE_DMA, this will cause CMA allocation > fail on some platforms, because CMA area could not across > different type of memory zones. > > Make CONFIG_ZONE_DMA configurable without EXPERT option > could let people build non debug kernel image with > CONFIG_ZONE_DMA disabled.
While I see why you need to toggle this feature, I'd rather try to figure out whether there is a better solution that does not break the single kernel image aim (i.e. the same config works for all supported SoCs).
When we decided to go ahead with a static 1GB ZONE_DMA for Raspberry Pi 4, we thought that other platforms would be fine, ZONE_DMA32 allocations fall back to ZONE_DMA. We missed the large CMA case.
I see a few potential options:
a) Ensure the CMA is contained within a single zone. How large is it in your case? Is it allocated by the kernel dynamically or a fixed start set by the boot loader?
b) Change the CMA allocator to allow spanning multiple zones (last time I looked it wasn't trivial since it relied on some per-zone lock).
c) Make ZONE_DMA dynamic on arm64 and only enable it if RPi4.
-- Catalin
| |