e7b079f4b6
Solving the DACR bug will mean that XN bits suddenly become enforced on non-LPAE systems, and we will no longer be able to execute out of a region mapped DCACHE_OFF. When we enable the MMU in romstage we are still executing out of SRAM, so we would instantly kill ourselves. Solve this issue by enabling the MMU earlier (in the bootblock) and mapping the SRAM regions as DCACHE_WRITETHROUGH. They should really be DCACHE_WRITEBACK, but it looks like there might be hardware limitations in the Cortex-A12 cache architecture that prevent us from doing so. Write-through mappings are equivalent to normal non-cacheable on the A12 anyway, and by using this attribute we don't need to introduce a new DCACHE_OFF_BUT_WITHOUT_XN_BIT type in our API. (Also, using normal non-cacheable might still have a slight speed advantage over strongly ordered since it should fetch whole cache lines at once if the processor finds enough accesses it can combine.) CQ-DEPEND=CL:223783 BUG=chrome-os-partner:32118 TEST=None (depends on follow-up CL) Change-Id: I53e827d95acc2db909f1251de78d65e295eceaa7 Signed-off-by: Julius Werner <jwerner@chromium.org> Reviewed-on: https://chromium-review.googlesource.com/223782 Reviewed-by: Aaron Durbin <adurbin@chromium.org> |
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