On Monday, March 31, 2014 at 09:21:38 AM, Stefano Babic wrote: > Hi Marek, > > On 28/03/2014 08:30, Marek Vasut wrote: > > Fix memory access slowness on i.MX53 MX53QSB board. Let us inspect the > > issue: First of all, the i.MX53 CPU has two memory banks mapped at > > 0x7000_0000 and 0xb000_0000 and each of those can hold up to 1GiB of > > DRAM memory. Notice that the memory area is not continuous. On MX53QSB, > > each of the banks contain 512MiB of DRAM, which makes a total of 1GiB > > of memory available to the system. > > > > The problem is how the relocation of U-Boot is treated on i.MX53 . The > > U-Boot is placed at the ((start of first DRAM partition) + > > (gd->ram_size)) . This in turn poses a problem, since in our case, the > > gd->ram_size is 1GiB, the first DRAM bank starts at 0x7000_0000 and > > contains 512MiB of memory. > > > > Thus, with this algorithm, U-Boot is placed at offset: > > 0x7000_0000 + 1GiB - sizeof(u-boot and some small margin) > > > > This is past the DRAM available in the first bank on MX53QSB, but is > > still within the address range of the first DRAM bank. Because of the > > memory wrap-around, the data can still be read and written to this area, > > but the access is much slower. > > > > There were two ideas how to solve this problem, first was to map both of > > the available DRAM chunks next to one another by using MMU, second was to > > define CONFIG_VERY_BIG_RAM and CONFIG_MAX_MEM_MAPPED to size of the > > memory in the first DRAM bank. We choose the later because it turns out > > the former is not applicable afterall. The former cannot be used in case > > Linux kernel was loaded into the second DRAM bank area, which would be > > remapped and one would try booting the kernel, since at some point > > before the kernel is started, the MMU would be turned off, which would > > destroy the mapping and hang the system. > > > > Signed-off-by: Marek Vasut <ma...@denx.de> > > Cc: Fabio Estevam <fabio.este...@freescale.com> > > Cc: Stefano Babic <sba...@denx.de> > > Cc: Wolfgang Denk <w...@denx.de> > > --- > > > > include/configs/mx53loco.h | 2 ++ > > 1 file changed, 2 insertions(+) > > > > V2: Reword the commit message > > > > diff --git a/include/configs/mx53loco.h b/include/configs/mx53loco.h > > index 1415584..82e0249 100644 > > --- a/include/configs/mx53loco.h > > +++ b/include/configs/mx53loco.h > > @@ -199,6 +199,8 @@ > > > > #define PHYS_SDRAM_2 CSD1_BASE_ADDR > > #define PHYS_SDRAM_2_SIZE (512 * 1024 * 1024) > > #define PHYS_SDRAM_SIZE (PHYS_SDRAM_1_SIZE + PHYS_SDRAM_2_SIZE) > > > > +#define CONFIG_VERY_BIG_RAM > > +#define CONFIG_MAX_MEM_MAPPED PHYS_SDRAM_1_SIZE > > > > #define CONFIG_SYS_SDRAM_BASE (PHYS_SDRAM_1) > > #define CONFIG_SYS_INIT_RAM_ADDR (IRAM_BASE_ADDR) > > Nice works, thanks ! I will push it soon.
Thanks :) There are a few more patches in your PW queue from me, please check them and apply as seen fit. Thanks again! Best regards, Marek Vasut _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
