On Fri, Mar 28, 2014 at 1:32 AM, Marek Vasut <ma...@denx.de> 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>
Excellent job, Marek! Ethernet transfers are 4 times faster now and overall boot time is greatly reduced :-) Tested-by: Fabio Estevam <fabio.este...@freescale.com> _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
