-----Original Message----- From: Bin Meng [mailto:bmeng.cn@gmail.com] Sent: Tuesday, January 22, 2019 7:37 AM To: Anup Patel Anup.Patel@wdc.com Cc: Rick Chen rick@andestech.com; Joe Hershberger joe.hershberger@ni.com; Lukas Auer lukas.auer@aisec.fraunhofer.de; Masahiro Yamada yamada.masahiro@socionext.com; Simon Glass sjg@chromium.org; Alexander Graf agraf@suse.de; Palmer Dabbelt palmer@sifive.com; Paul Walmsley paul.walmsley@sifive.com; Atish Patra Atish.Patra@wdc.com; Christoph Hellwig hch@infradead.org; U- Boot Mailing List u-boot@lists.denx.de Subject: Re: [PATCH v2 03/11] riscv: generic: Ensure that U-Boot runs within 4GB for 64bit systems
On Fri, Jan 18, 2019 at 7:19 PM Anup Patel Anup.Patel@wdc.com wrote:
On 64bit systems, the DRAM top can be easily beyond 4GB and U-Boot
DMA
mapping APIs will generate DMA addresses beyond 4GB. This breaks DMA programming in 32bit DMA capable devices (such as Cadence MACB ethernet). For example, If DRAM is more then 2GB on QEMU sifive_u machine then Cadence MACB ethernet stops working for U-Boot because
it
is a 32bit DMA capable device.
To handle 32bit DMA capable devices on 64bit systems, we provide custom implementation of board_get_usable_ram_top() which ensures
that
usable ram top is not more then 4GB. This in-turn ensures that U-Boot always runs within 4GB hence DMA addresses generated by DMA mapping APIs will be within 4GB too.
Signed-off-by: Atish Patra atish.patra@wdc.com Signed-off-by: Anup Patel anup.patel@wdc.com Reviewed-by: Alexander Graf agraf@suse.de
arch/riscv/cpu/generic/dram.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)
Reviewed-by: Bin Meng bmeng.cn@gmail.com
But see one comment below:
diff --git a/arch/riscv/cpu/generic/dram.c b/arch/riscv/cpu/generic/dram.c index 84d87d2a7f..5725d3c7ae 100644 --- a/arch/riscv/cpu/generic/dram.c +++ b/arch/riscv/cpu/generic/dram.c @@ -5,6 +5,9 @@
#include <common.h> #include <fdtdec.h> +#include <linux/sizes.h>
+DECLARE_GLOBAL_DATA_PTR;
int dram_init(void) { @@ -15,3 +18,20 @@ int dram_init_banksize(void) { return fdtdec_setup_memory_banksize(); }
+ulong board_get_usable_ram_top(ulong total_size) { #ifdef +CONFIG_64BIT
/** Ensure that we run from first 4GB so that all* addresses used by U-Boot are 32bit addresses.** This in-turn ensures that 32bit DMA capabale* devices work fine because DMA mapping APIs will* provide 32bit DMA addresses only.*/if (gd->ram_top > SZ_4G)return SZ_4G;+#endif
return gd->ram_top;+}
I was wondering whether we should change this for 32-bit too, given it's a valid configuration to have more than 4GB memory in a 32-bit system.
We had considered this but "gd->ram_top" is "unsigned long" so on 32bit system it will be 32bit only. In other words, value of "gd->ram_top" on 32bit system can never exceed 4GB.
Regards, Anup