On Mon, Sep 14, 2026 at 12:31:31PM +0530, Aneesh Kumar K.V (Arm) wrote:
> NOTE: We lose the RISC-V SWIOTLB_ANY setting in this patch. It will be
> reinstated in a follow-up patch where we make SWIOTLB_ANY redundant.
[...]
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index e0e4c103d603..734712230f35 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -165,31 +165,11 @@ static void print_vm_layout(void) { }
>
> void __init arch_mm_preinit(void)
> {
> - bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit) &&
> - memblock_start_of_DRAM() < dma32_phys_limit;
> unsigned int swiotlb_flags = SWIOTLB_VERBOSE;
> #ifdef CONFIG_FLATMEM
> BUG_ON(!mem_map);
> #endif /* CONFIG_FLATMEM */
>
> - if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb &&
> - dma_cache_alignment != 1) {
> - /*
> - * No 32-bit DMA bouncing needed (either all DRAM is within
> - * the 32-bit limit, or it all starts above it), but
> - * kmalloc() buffers whose sizes are not cache-line-aligned
> - * still require bouncing for non-coherent DMA. Use
> - * SWIOTLB_ANY so that the buffer can be allocated from high
> - * memory when DRAM starts above dma32_phys_limit. Allocate
> - * ~1 MB per 1 GB of RAM.
> - */
> - unsigned long size =
> - DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
> - swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
> - swiotlb = true;
> - swiotlb_flags |= SWIOTLB_ANY;
> - }
Does it break the bisectability for risc-v? IIUC this undoes commit
cfca5a48b03f until patch 5. Basically if there's no low memory and no
SWIOTLB_ANY passed, memblock_alloc_low() will fail.
I think we could preserve SWIOTLB_ANY until patch 5. Or it might be
simpler to move patches 2 and 3 at the end (I haven't tried).
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index aa19e81ae544..90e0bfd0715c 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -304,6 +304,11 @@ unsigned long swiotlb_size_or_default(void)
> return default_nslabs << IO_TLB_SHIFT;
> }
>
> +static bool __init swiotlb_default_size_changed(void)
> +{
> + return default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
> +}
I mentioned before in passing
(https://lore.kernel.org/all/[email protected]/), if one sets
swiotlb= to the default size, it will go unnoticed. I know it's an
existing issue but we might as well fix it now with a bool that tells us
the swiotlb size was forced/changed.
--
Catalin
