| Message ID | 20201014191211.27029-7-nsaenzjulienne@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Default to 32-bit wide ZONE_DMA | expand |
On Wed, Oct 14, 2020 at 09:12:08PM +0200, Nicolas Saenz Julienne wrote: > + zone_dma_bits = min(zone_dma_bits, > + (unsigned int)ilog2(of_dma_get_max_cpu_address(NULL))); Plase avoid pointlessly long lines. Especially if it is completely trivial by using either min_t or not overindenting like here.
On Thu, 2020-10-15 at 07:39 +0200, Christoph Hellwig wrote: > On Wed, Oct 14, 2020 at 09:12:08PM +0200, Nicolas Saenz Julienne wrote: > > + zone_dma_bits = min(zone_dma_bits, > > + (unsigned int)ilog2(of_dma_get_max_cpu_address(NULL))); > > Plase avoid pointlessly long lines. Especially if it is completely trivial > by using either min_t or not overindenting like here. Noted
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index fce8cbecd6bc..c09d3f1a9a6b 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -97,6 +97,7 @@ extern phys_addr_t arm64_dma_phys_limit; #define ARCH_LOW_ADDRESS_LIMIT (arm64_dma_phys_limit - 1) +#define ZONE_DMA_BITS_DEFAULT 32 struct debug_info { #ifdef CONFIG_HAVE_HW_BREAKPOINT diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index ef0ef0087e2c..97b0d2768349 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -42,8 +42,6 @@ #include <asm/tlb.h> #include <asm/alternative.h> -#define ARM64_ZONE_DMA_BITS 30 - /* * We need to be able to catch inadvertent references to memstart_addr * that occur (potentially in generic code) before arm64_memblock_init() @@ -196,7 +194,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max) unsigned long max_zone_pfns[MAX_NR_ZONES] = {0}; #ifdef CONFIG_ZONE_DMA - zone_dma_bits = ARM64_ZONE_DMA_BITS; + zone_dma_bits = min(zone_dma_bits, + (unsigned int)ilog2(of_dma_get_max_cpu_address(NULL))); arm64_dma_phys_limit = max_zone_phys(zone_dma_bits); max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit); #endif
We recently introduced a 1 GB sized ZONE_DMA to cater for platforms incorporating masters that can address less than 32 bits of DMA, in particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has peripherals that can only address up to 1 GB (and its PCIe host bridge can only access the bottom 3 GB) The DMA layer also needs to be able to allocate memory that is guaranteed to meet those DMA constraints, for bounce buffering as well as allocating the backing for consistent mappings. This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately, it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes problems with kdump, and potentially in other places where allocations cannot cross zone boundaries. Therefore, we should avoid having two separate DMA zones when possible. So, with the help of of_dma_get_max_cpu_address() get the topmost physical address accessible to all DMA masters in system and use that information to fine-tune ZONE_DMA's size. In the absence of addressing limited masters ZONE_DMA will span the whole 32-bit address space, otherwise, in the case of the Raspberry Pi 4 it'll only span the 30-bit address space, and have ZONE_DMA32 cover the rest of the 32-bit address space. Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de> --- Changes since v2: - Updated commit log by shamelessly copying Ard's ACPI counterpart commit log arch/arm64/include/asm/processor.h | 1 + arch/arm64/mm/init.c | 5 ++--- 2 files changed, 3 insertions(+), 3 deletions(-)