Commits
James Hogan committed 37fb60f8e3f
MIPS: Add defs & probing of extended CP0_EBase The CP0_EBase register may optionally have a write gate (WG) bit to allow the upper bits to be written, i.e. bits 31:30 on MIPS32 since r3 (to allow for an exception base outside of KSeg0/KSeg1 when segmentation control is in use) and bits 63:30 on MIPS64 (which also implies the extension of CP0_EBase to 64 bits long). The presence of this feature will need to be known about for VZ support in order to correctly save and restore all the bits of the guest CP0_EBase register, so add CPU feature definition and probing for this feature. Probing the WG bit on MIPS64 can be a bit fiddly, since 64-bit COP0 register access instructions were UNDEFINED for 32-bit registers prior to MIPS r6, and it'd be nice to be able to probe without clobbering the existing state, so there are 3 potential paths: - If we do a 32-bit read of CP0_EBase and the WG bit is already set, the register must be 64-bit. - On MIPS r6 we can do a 64-bit read-modify-write to set CP0_EBase.WG, since the upper bits will read 0 and be ignored on write if the register is 32-bit. - On pre-r6 cores, we do a 32-bit read-modify-write of CP0_EBase. This avoids the potentially UNDEFINED behaviour, but will clobber the upper 32-bits of CP0_EBase if it isn't a simple sign extension (which also requires us to ensure BEV=1 or modifying the exception base would be UNDEFINED too). It is hopefully unlikely a bootloader would set up CP0_EBase to a 64-bit segment and leave WG=0. [ralf@linux-mips.org: Resolved merge conflict.] Signed-off-by: James Hogan <james.hogan@imgtec.com> Tested-by: Matt Redfearn <matt.redfearn@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/13223/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>