On Mon, Oct 31, 2016 at 04:45:04PM +0100, Geert Uytterhoeven wrote:
> On architectures like arm64, swiotlb is tied intimately to the core
> architecture DMA support. In addition, ZONE_DMA cannot be disabled.
>
> To aid debugging and catch devices not supporting DMA to memory outside
> the 32-bit address space, add a kernel command line option
> "swiotlb=nobounce", which disables the use of bounce buffers.
> If specified, trying to map memory that cannot be used with DMA will
> fail, and a warning will be printed (rate-limited).
I would make the 'swiotlb_force' an enum. And then instead of this
being 'nobounce' just do the inverse of 'force', that is the
'noforce' would trigger this no bounce effect.
So:
enum {
NORMAL, /* Default - depending on the hardware DMA mask and such. */
FORCE, /* swiotlb=force */
NO_FORCE, /* swiotlb=noforce */
}
>
> Note that io_tlb_nslabs is set to 1, which is the minimal supported
> value.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> ---
> Documentation/kernel-parameters.txt | 3 ++-
> lib/swiotlb.c | 19 +++++++++++++++++--
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 37babf91f2cb6de2..38556cdceabaf087 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3998,10 +3998,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> it if 0 is given (See Documentation/cgroup-v1/memory.txt)
>
> swiotlb= [ARM,IA-64,PPC,MIPS,X86]
> - Format: { <int> | force }
> + Format: { <int> | force | nobounce }
> <int> -- Number of I/O TLB slabs
> force -- force using of bounce buffers even if they
> wouldn't be automatically used by the kernel
> + nobounce -- Never use bounce buffers (for debugging)
>
> switches= [HW,M68k]
>
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 6ce764410ae475cc..4550e6b516c2a4c0 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -54,6 +54,7 @@
> #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
>
> int swiotlb_force;
> +static int swiotlb_nobounce;
>
> /*
> * Used to do a quick range check in swiotlb_tbl_unmap_single and
> @@ -106,8 +107,12 @@
> }
> if (*str == ',')
> ++str;
> - if (!strcmp(str, "force"))
> + if (!strcmp(str, "force")) {
> swiotlb_force = 1;
> + } else if (!strcmp(str, "nobounce")) {
> + swiotlb_nobounce = 1;
> + io_tlb_nslabs = 1;
> + }
>
> return 0;
> }
> @@ -541,8 +546,15 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
> map_single(struct device *hwdev, phys_addr_t phys, size_t size,
> enum dma_data_direction dir)
> {
> - dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
> + dma_addr_t start_dma_addr;
> +
> + if (swiotlb_nobounce) {
> + dev_warn_ratelimited(hwdev, "Cannot do DMA to address %pa\n",
> + &phys);
> + return SWIOTLB_MAP_ERROR;
> + }
>
> + start_dma_addr = phys_to_dma(hwdev, io_tlb_start);
> return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size, dir);
> }
>
> @@ -707,6 +719,9 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
> swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir,
> int do_panic)
> {
> + if (swiotlb_nobounce)
> + return;
> +
> /*
> * Ran out of IOMMU space for this operation. This is very bad.
> * Unfortunately the drivers cannot handle this operation properly.
> --
> 1.9.1
>
