On Friday, March 28, 2014 at 05:32:42 AM, 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 non-continuous memory > partitions mapped at 0x7000_0000 and 0xb000_0000 and each of those can > hold up to 1GiB of DRAM memory. On MX53QSB, each of the partitions contain > 512MiB of DRAM, which makes a total of 1GiB of memory available to the > platform. > > 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 partition starts at 0x7000_0000 and contains 512MiB > of data. Thus, with this algorithm, U-Boot is placed at offset 0x7000_0000 > + 1GiB, which is past the DRAM available in the first partition on > MX53QSB, but is still within the address range of the first DRAM > partition. Because of memory wrap-around, this bug was well hidden. > > There were two ideas how to solve this problem, first was to map both of > the DRAM 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 partition. 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 partition 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>
Fabio, please check the rest of the MX5x series so we squash this and don't produce additional technological debt here. Thanks ! Best regards, Marek Vasut _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
