[U-Boot] [PATCH V2 3/4] arm: mx5: Fix memory slowness on M53EVK

[Stefano Babic]

On 28/03/2014 08:31, Marek Vasut wrote:
> Fix memory access slowness on i.MX53 M53EVK 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 M53EVK,
> 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 M53EVK, 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 <marex at denx.de>
> Cc: Fabio Estevam <fabio.estevam at freescale.com>
> Cc: Stefano Babic <sbabic at denx.de>
> Cc: Wolfgang Denk <wd at denx.de>
> ---

Applied to u-boot-imx, thanks !

Best regards,
Stefano Babic


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