Messages in this thread | | | Subject | Re: [PATCH] swiotlb: Add swiotlb=off to disable SWIOTLB | From | Robin Murphy <> | Date | Thu, 18 Mar 2021 19:34:55 +0000 |
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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.
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 ;)
Robin.
> right now this is made unconditional whenever ARM_LPAE is enabled which > is the case for the platforms I maintain (ARCH_BRCMSTB) however we do > not really need a SWIOTLB so long as the largest DRAM physical address > does not exceed 4GB AFAICT. > > Thanks! > >> --- >> Documentation/admin-guide/kernel-parameters.txt | 1 + >> include/linux/swiotlb.h | 1 + >> kernel/dma/swiotlb.c | 9 +++++++++ >> 3 files changed, 11 insertions(+) >> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >> index 04545725f187..b0223e48921e 100644 >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -5278,6 +5278,7 @@ >> force -- force using of bounce buffers even if they >> wouldn't be automatically used by the kernel >> noforce -- Never use bounce buffers (for debugging) >> + off -- Completely disable SWIOTLB >> >> switches= [HW,M68k] >> >> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h >> index 5857a937c637..23f86243defe 100644 >> --- a/include/linux/swiotlb.h >> +++ b/include/linux/swiotlb.h >> @@ -15,6 +15,7 @@ enum swiotlb_force { >> SWIOTLB_NORMAL, /* Default - depending on HW DMA mask etc. */ >> SWIOTLB_FORCE, /* swiotlb=force */ >> SWIOTLB_NO_FORCE, /* swiotlb=noforce */ >> + SWIOTLB_OFF, /* swiotlb=off */ >> }; >> >> /* >> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c >> index c10e855a03bc..d7a4a789c7d3 100644 >> --- a/kernel/dma/swiotlb.c >> +++ b/kernel/dma/swiotlb.c >> @@ -126,6 +126,8 @@ setup_io_tlb_npages(char *str) >> } else if (!strcmp(str, "noforce")) { >> swiotlb_force = SWIOTLB_NO_FORCE; >> io_tlb_nslabs = 1; >> + } else if (!strcmp(str, "off")) { >> + swiotlb_force = SWIOTLB_OFF; >> } >> >> return 0; >> @@ -229,6 +231,9 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose) >> unsigned long i, bytes; >> size_t alloc_size; >> >> + if (swiotlb_force == SWIOTLB_OFF) >> + return 0; >> + >> bytes = nslabs << IO_TLB_SHIFT; >> >> io_tlb_nslabs = nslabs; >> @@ -284,6 +289,9 @@ swiotlb_init(int verbose) >> unsigned char *vstart; >> unsigned long bytes; >> >> + if (swiotlb_force == SWIOTLB_OFF) >> + goto out; >> + >> if (!io_tlb_nslabs) { >> io_tlb_nslabs = (default_size >> IO_TLB_SHIFT); >> io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE); >> @@ -302,6 +310,7 @@ swiotlb_init(int verbose) >> io_tlb_start = 0; >> } >> pr_warn("Cannot allocate buffer"); >> +out: >> no_iotlb_memory = true; >> } >> >> >
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