Messages in this thread |  | | From | Peng Fan <> | Subject | RE: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable without EXPERT | Date | Wed, 25 Mar 2020 12:30:11 +0000 |
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> Subject: Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable > without EXPERT > > On Wed, Mar 25, 2020 at 12:34:15AM +0000, Peng Fan wrote: > > > 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. > > > > This will break legacy dts with new version kernel. > > > > > How large is it in your case? > > > > It is 1GB > > > > > Is it allocated by the kernel dynamically or a fixed start set by > > > the boot loader? > > > > We use alloc-ranges and size in kernel dts. > > > > But there is only 2GB DRAM in the board. > > So I guess without changing the dts, option (a) doesn't really work. > > > > 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. > > > > Option c seems a bit easier to me :) > > > > I will try to explore both, but if you have time to help, that would > > be appreciated. > > I don't have time but option (c) was already discussed and there are patches > from Nicolas on the list: > > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke > rnel.org%2Flinux-arm-kernel%2F20190820145821.27214-5-nsaenzjulienne% > 40suse.de%2F&data=02%7C01%7Cpeng.fan%40nxp.com%7C6403ddf37 > 89b452ae5ee08d7d0a5a659%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0 > %7C0%7C637207282191026738&sdata=t2cZ9HTCcRuaL9RO4kD%2BzN > 2n4VqM%2F66zYNZIOComCVs%3D&reserved=0 > > The above series was checking whether the platform is RPi4 and limiting the > ZONE_DMA size to 1GB (otherwise 4GB with ZONE_DMA32 empty). We > ended up with a static 1GB for ZONE_DMA but we missed the fact that it may > break existing platforms.
Thanks for the information. I'll check the patchset and work out something proper to fix the issue I met.
Thanks, Peng.
> > So I don't think it would be too hard to revive the above series (most of it was > already merged). > > -- > Catalin
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