| Message ID | 20140718110718.GC19850@arm.com |
|---|---|
| State | Accepted |
| Commit | d50314a6b0702c630c35b88148c1acb76d2e4ede |
| Headers | show |
On Fri, 2014-07-18 at 12:07 +0100, Catalin Marinas wrote: > On Tue, Jun 24, 2014 at 03:38:34PM +0100, Mark Salter wrote: > > On Tue, 2014-06-24 at 15:14 +0100, Catalin Marinas wrote: > > > On Mon, Jun 23, 2014 at 02:17:03PM +0100, Mark Salter wrote: > > > > On Mon, 2014-06-23 at 12:09 +0100, Catalin Marinas wrote: > > > > > My proposal (in the absence of any kind of description) is to still > > > > > create a ZONE_DMA if we have DMA memory below 32-bit, otherwise just add > > > > > everything (>32-bit) to ZONE_DMA. Basically an extension from your CMA > > > > > patch, make dma_phys_limit static in that file and set it to > > > > > memblock_end_of_DRAM() if no 32-bit DMA. Re-use it in the > > > > > zone_sizes_init() function for ZONE_DMA (maybe with a pr_info for no > > > > > 32-bit only DMA zone). > > > > > > > > There's a performance issue with all memory being in ZONE_DMA. It means > > > > all normal allocations will fail on ZONE_NORMAL and then have to fall > > > > back to ZONE_DMA. It would be better to put some percentage of memory > > > > in ZONE_DMA. > > > > > > Is the performance penalty real or just theoretical? I haven't run any > > > benchmarks myself. > > > > It is real insofar as you must eat cycles eliminating ZONE_NORMAL from > > consideration in the page allocation hot path. How much that really > > costs, I don't know. But it seems like it could be easily avoided by > > limiting ZONE_DMA size. Is there any reason it needs to be larger than > > 4GiB? > > Basically ZONE_DMA should allow a 32-bit dma mask. When memory starts > above 4G, in the absence of an IOMMU, it is likely that 32-bit devices > get some offset for the top bits to be able to address the bottom of the > memory. The problem is that dma_to_phys() that early in the kernel has > no idea about DMA offsets until later (they can be specified in DT per > device). > > The patch belows tries to guess a DMA offset and use the bottom 32-bit > of the DRAM as ZONE_DMA. > > -------8<----------------------- > > From 133656f8378dbb838ad5f12ea29aa9303d7ca922 Mon Sep 17 00:00:00 2001 > From: Catalin Marinas <catalin.marinas@arm.com> > Date: Fri, 18 Jul 2014 11:54:37 +0100 > Subject: [PATCH] arm64: Create non-empty ZONE_DMA when DRAM starts above 4GB > > ZONE_DMA is created to allow 32-bit only devices to access memory in the > absence of an IOMMU. On systems where the memory starts above 4GB, it is > expected that some devices have a DMA offset hardwired to be able to > access the bottom of the memory. Linux currently supports DT bindings > for the DMA offsets but they are not (easily) available early during > boot. > > This patch tries to guess a DMA offset and assumes that ZONE_DMA > corresponds to the 32-bit mask above the start of DRAM. > > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> > Cc: Mark Salter <msalter@redhat.com> > --- Tested-by: Mark Salter <msalter@redhat.com> Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 7f68804814a1..160bbaa4fc78 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -60,6 +60,17 @@ static int __init early_initrd(char *p) early_param("initrd", early_initrd); #endif +/* + * Return the maximum physical address for ZONE_DMA (DMA_BIT_MASK(32)). It + * currently assumes that for memory starting above 4G, 32-bit devices will + * use a DMA offset. + */ +static phys_addr_t max_zone_dma_phys(void) +{ + phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, 32); + return min(offset + (1ULL << 32), memblock_end_of_DRAM()); +} + static void __init zone_sizes_init(unsigned long min, unsigned long max) { struct memblock_region *reg; @@ -70,9 +81,7 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max) /* 4GB maximum for 32-bit only capable devices */ if (IS_ENABLED(CONFIG_ZONE_DMA)) { - unsigned long max_dma_phys = - (unsigned long)(dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1); - max_dma = max(min, min(max, max_dma_phys >> PAGE_SHIFT)); + max_dma = PFN_DOWN(max_zone_dma_phys()); zone_size[ZONE_DMA] = max_dma - min; } zone_size[ZONE_NORMAL] = max - max_dma; @@ -142,7 +151,7 @@ void __init arm64_memblock_init(void) /* 4GB maximum for 32-bit only capable devices */ if (IS_ENABLED(CONFIG_ZONE_DMA)) - dma_phys_limit = dma_to_phys(NULL, DMA_BIT_MASK(32)) + 1; + dma_phys_limit = max_zone_dma_phys(); dma_contiguous_reserve(dma_phys_limit); memblock_allow_resize();