From d3b7fd74f7b42acaa85fda67974445b62b4840ca Mon Sep 17 00:00:00 2001 From: Thierry Reding Date: Mon, 27 Jul 2015 11:45:24 -0600 Subject: [PATCH] ARM: tegra: Restrict usable RAM to 32-bit on 64-bit SoCs Most peripherals on Tegra can do DMA only to the lower 32-bit address space, even on 64-bit SoCs. This limitation is typically overcome by the use of an IOMMU. Since the IOMMU is not entirely trivial to set up and serves no other purpose (I/O protection, ...) in U-Boot, restrict 64-bit Tegra SoCs to the lower 32-bit address space for RAM. This ensures that the physical addresses of buffers that are programmed into the various DMA engines are valid and don't alias to lower addresses. Signed-off-by: Thierry Reding Signed-off-by: Tom Warren Signed-off-by: Stephen Warren --- arch/arm/mach-tegra/board2.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/arm/mach-tegra/board2.c b/arch/arm/mach-tegra/board2.c index ce9b6959ef..e0d8687cbc 100644 --- a/arch/arm/mach-tegra/board2.c +++ b/arch/arm/mach-tegra/board2.c @@ -274,3 +274,19 @@ void pad_init_mmc(struct mmc_host *host) #endif /* T30 */ } #endif /* MMC */ + +#ifdef CONFIG_ARM64 +/* + * Most hardware on 64-bit Tegra is still restricted to DMA to the lower + * 32-bits of the physical address space. Cap the maximum usable RAM area + * at 4 GiB to avoid DMA buffers from being allocated beyond the 32-bit + * boundary that most devices can address. + */ +ulong board_get_usable_ram_top(ulong total_size) +{ + if (gd->ram_top > 0x100000000) + return 0x100000000; + + return gd->ram_top; +} +#endif -- 2.39.5