Messages in this thread | | | Subject | Re: [PATCH] swiotlb: Add swiotlb=off to disable SWIOTLB | From | Robin Murphy <> | Date | Thu, 18 Mar 2021 19:53:37 +0000 |
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On 2021-03-18 19:43, Florian Fainelli wrote: > > > On 3/18/2021 12:34 PM, Robin Murphy wrote: >> On 2021-03-18 19:22, Florian Fainelli wrote: >>> >>> >>> On 3/18/2021 12:18 PM, Florian Fainelli wrote: >>>> It may be useful to disable the SWIOTLB completely for testing or when a >>>> platform is known not to have any DRAM addressing limitations what so >>>> ever. >> >> Isn't that what "swiotlb=noforce" is for? If you're confident that we've >> really ironed out *all* the awkward corners that used to blow up if >> various internal bits were left uninitialised, then it would make sense >> to just tweak the implementation of what we already have. > > swiotlb=noforce does prevent dma_direct_map_page() from resorting to the > swiotlb, however what I am also after is reclaiming these 64MB of > default SWIOTLB bounce buffering memory because my systems run with > large amounts of reserved memory into ZONE_MOVABLE and everything in > ZONE_NORMAL is precious at that point.
It also forces io_tlb_nslabs to the minimum, so it should be claiming considerably less than 64MB. IIRC the original proposal *did* skip initialisation completely, but that turned up the aforementioned issues.
>> I wouldn't necessarily disagree with adding "off" as an additional alias >> for "noforce", though, since it does come across as a bit wacky for >> general use. >> >>>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> >>> >>> Christoph, in addition to this change, how would you feel if we >>> qualified the swiotlb_init() in arch/arm/mm/init.c with a: >>> >>> >>> if (memblock_end_of_DRAM() >= SZ_4G) >>> swiotlb_init(1) >> >> Modulo "swiotlb=force", of course ;) > > Indeed, we would need to handle that case as well. Does it sound > reasonable to do that to you as well?
I wouldn't like it done to me personally, but for arm64, observe what mem_init() in arch/arm64/mm/init.c already does.
Robin.
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