From: Nicolas Saenz Julienne nsaenzjulienne@suse.de
commit 8424ecdde7df99d5426e1a1fd9f0fb36f4183032 upstream
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 Link: https://lore.kernel.org/r/20201119175400.9995-6-nsaenzjulienne@suse.de Signed-off-by: Catalin Marinas catalin.marinas@arm.com Cc: stable@vger.kernel.org Signed-off-by: Jing Xiangfeng jingxiangfeng@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/mm/init.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- 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() @@ -188,9 +186,11 @@ static phys_addr_t __init max_zone_phys( static void __init zone_sizes_init(unsigned long min, unsigned long max) { unsigned long max_zone_pfns[MAX_NR_ZONES] = {0}; + unsigned int __maybe_unused dt_zone_dma_bits;
#ifdef CONFIG_ZONE_DMA - zone_dma_bits = ARM64_ZONE_DMA_BITS; + dt_zone_dma_bits = fls64(of_dma_get_max_cpu_address(NULL)); + zone_dma_bits = min(32U, dt_zone_dma_bits); arm64_dma_phys_limit = max_zone_phys(zone_dma_bits); max_zone_pfns[ZONE_DMA] = PFN_DOWN(arm64_dma_phys_limit); #endif