Catalin Marinas <[email protected]> writes:
> 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 mentioned this in the commit message. I can add the change below and
remove it in patch 5.
modified arch/riscv/mm/init.c
@@ -165,11 +165,27 @@ 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.
+ */
+ swiotlb_flags |= SWIOTLB_ANY;
+ }
+
if ((max_pfn > PFN_DOWN(dma32_phys_limit)) &&
(memblock_start_of_DRAM() < dma32_phys_limit))
swiotlb_flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;
>
> 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.
>
I will do this as an addtional patch
modified kernel/dma/swiotlb.c
@@ -108,6 +108,7 @@
static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
static unsigned long default_nareas;
+static bool swiotlb_size_set __initdata;
/**
* struct io_tlb_area - IO TLB memory area descriptor
@@ -270,6 +271,7 @@
/* avoid tail segment of size < IO_TLB_SEGSIZE */
default_nslabs =
ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE);
+ swiotlb_size_set = true;
}
if (*str == ',')
++str;
@@ -307,7 +309,7 @@
static bool __init swiotlb_default_size_changed(void)
{
- return default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
+ return swiotlb_size_set;
}
void __init swiotlb_adjust_size(unsigned long size)
