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https://github.com/brain-hackers/u-boot-brain
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Before main memory (DDR) is initialized, the on-chip L1 cache is used as a memory area for the stack and the global data (gd_t) structure. This is called the initial RAM area, or initram. The L1 cache is locked and the TLBs point to a non-existent address (so that there's no chance it will overlap main memory or any device). The L1 cache is also configured not to write out to memory or the L2 cache, so everything stays in the L1 cache. One of the things we might do while running out of initram is relocate CCSR. On reset, CCSR is typically located at some high 32-bit address, like 0xfe000000, and this may not be the best place for CCSR. For example, on 36-bit systems, CCSR is relocated to 0xffe000000, near the top of 36-bit memory space. On some future Freescale SOCs, the L1 cache will be forced to write to the backing store, so we can no longer have the TLBs point to non-existent address. Instead, we will point the TLBs to an unused area in CCSR. In order for this technique to work, CCSR needs to be relocated before the initram memory is enabled. Unlike the original CCSR relocation code in cpu_init_early_f(), the TLBs we create now for relocating CCSR are deleted after the relocation is finished. cpu_init_early_f() will still need to create a TLB for CCSR (at the new location) for normal U-Boot purposes. This is done to keep the impact to existing U-Boot code minimal and to better isolate the CCSR relocation code. Signed-off-by: Timur Tabi <timur@freescale.com> Signed-off-by: Kumar Gala <galak@kernel.crashing.org> |
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