Messages in this thread Patch in this message | | | Date | Wed, 30 Mar 2022 17:24:56 +0800 | Subject | Re: [PATCH 1/2] arm64: mm: Do not defer reserve_crashkernel() if only ZONE_DMA32 | From | Kefeng Wang <> |
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On 2022/3/30 6:29, Vijay Balakrishna wrote: > > > On 3/24/2022 10:53 PM, Kefeng Wang wrote: >> The kernel could be benifit due to BLOCK_MAPPINGS, see commit >> 031495635b46 ("arm64: Do not defer reserve_crashkernel() for >> platforms with no DMA memory zones"), if there is only with >> ZONE_DMA32, we could set arm64_dma_phys_limit to max_zone_phys(32) >> earlier in arm64_memblock_init(), then we will benifit too. > > Thanks for noticing platforms with just ZONE_DMA32 config can also > benefit BLOCK_MAPPINGS. I assume you have access to one where you > notice the difference with proposed changes and able to test. I did > test proposed changes on SoC we use with IOMMU (no ZONE_DMA configs > enabled). > > Nits -- > - benifit -> benefit > - consider making commit message clear, "then we will.." seems you are > referring to platforms with just ZONE_DMA32 config enabled > - to reflect new change consider updating comment added in commit > 031495635b46 > One more question, could we add new cmdline(eg, dma_force_32bit) to let the arm64 using
32bit dma by default? I think most platforms are not with small DMA bit(only found 20bit in Raspberry Pi 4?),
Here is a draft(based on this patch) to do it, if the kernel boot with this cmdline and even ZONE_DMA
is enabled, the kernel allows linear creation of block mapping, not sure this is the right way, any suggestion? Thanks.
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h index 73e38d9a540c..8febed26aeed 100644 --- a/arch/arm64/include/asm/processor.h +++ b/arch/arm64/include/asm/processor.h @@ -100,6 +100,7 @@ base) #endif /* CONFIG_ARM64_FORCE_52BIT */
+extern bool arm64_dma_force_32bit; extern phys_addr_t arm64_dma_phys_limit; #define ARCH_LOW_ADDRESS_LIMIT (arm64_dma_phys_limit - 1)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index d6f64819ef89..86aab5db735b 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -92,6 +92,16 @@ phys_addr_t __ro_after_init arm64_dma_phys_limit; phys_addr_t __ro_after_init arm64_dma_phys_limit = PHYS_MASK + 1; #endif
+bool __ro_after_init arm64_dma_force_32bit; +static int __init arm64_dma_force_32bit_setup(char *p) +{ + arm64_dma_force_32bit = true; + zone_dma_bits = 32; + + return 0; +} +early_param("dma_force_32bit", arm64_dma_force_32bit_setup); + /* * reserve_crashkernel() - reserves memory for crash kernel * @@ -165,10 +175,11 @@ static void __init zone_sizes_init(void) #ifdef CONFIG_ZONE_DMA unsigned int acpi_zone_dma_bits; unsigned int dt_zone_dma_bits; - - acpi_zone_dma_bits = fls64(acpi_iort_dma_get_max_cpu_address()); - dt_zone_dma_bits = fls64(of_dma_get_max_cpu_address(NULL)); - zone_dma_bits = min3(32U, dt_zone_dma_bits, acpi_zone_dma_bits); + if (!arm64_dma_force_32bit) { + acpi_zone_dma_bits = fls64(acpi_iort_dma_get_max_cpu_address()); + dt_zone_dma_bits = fls64(of_dma_get_max_cpu_address(NULL)); + zone_dma_bits = min3(32U, dt_zone_dma_bits, acpi_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 @@ -336,7 +347,7 @@ void __init arm64_memblock_init(void) early_init_fdt_scan_reserved_mem();
dma32_phys_limit = max_zone_phys(32); - if (!IS_ENABLED(CONFIG_ZONE_DMA)) { + if (!IS_ENABLED(CONFIG_ZONE_DMA) || arm64_dma_force_32bit) { if (IS_ENABLED(CONFIG_ZONE_DMA32)) arm64_dma_phys_limit = dma32_phys_limit; reserve_crashkernel(); @@ -388,7 +399,7 @@ void __init bootmem_init(void) * request_standard_resources() depends on crashkernel's memory being * reserved, so do it here. */ - if (IS_ENABLED(CONFIG_ZONE_DMA)) + if (IS_ENABLED(CONFIG_ZONE_DMA) && !arm64_dma_force_32bit) reserve_crashkernel();
memblock_dump_all(); diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 23734481318a..9431ad581927 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -529,7 +529,7 @@ static void __init map_mem(pgd_t *pgdp)
#ifdef CONFIG_KEXEC_CORE if (crash_mem_map) { - if (IS_ENABLED(CONFIG_ZONE_DMA)) + if (IS_ENABLED(CONFIG_ZONE_DMA) && !arm64_dma_force_32bit) flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; else if (crashk_res.end) memblock_mark_nomap(crashk_res.start, @@ -570,7 +570,7 @@ static void __init map_mem(pgd_t *pgdp) * through /sys/kernel/kexec_crash_size interface. */ #ifdef CONFIG_KEXEC_CORE - if (crash_mem_map && !IS_ENABLED(CONFIG_ZONE_DMA)) { + if (crash_mem_map && (!IS_ENABLED(CONFIG_ZONE_DMA) || arm64_dma_force_32bit)) { if (crashk_res.end) { __map_memblock(pgdp, crashk_res.start, crashk_res.end + 1,
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