kernel/linux.git/arch/mips/include/asm/stackframe.h, branch v6.19.11

MIPS: Take in account load hazards for HI/LO restoring

2024-05-03T12:22:38+00:00

MIPS CPUs usually have 1 to 4 cycles load hazards, thus doing load and right after move to HI/LO will usually stall the pipeline for significant amount of time. Let's take it into account and separate loads and mthi/lo in instruction sequence. The patch uses t6 and t7 registers as temporaries in addition to t8. The patch tries to deal with SmartMIPS, but I know little about and haven't tested it. Changes in v2: - clear separation of actions for SmartMIPS and pre-MIPSR6. Signed-off-by: Siarhei Volkau Signed-off-by: Thomas Bogendoerfer

MIPS: Remove TX39XX support

2022-03-01T09:07:22+00:00

No (active) developer owns this hardware, so let's remove Linux support. Signed-off-by: Thomas Bogendoerfer Acked-by: Guenter Roeck Reviewed-by: Geert Uytterhoeven Tested-by: Geert Uytterhoeven Acked-by: Atsushi Nemoto

MIPS: Loongson-3: Enable COP2 usage in kernel

2020-09-21T20:15:03+00:00

Loongson-3's COP2 is Multi-Media coprocessor, it is disabled in kernel mode by default. However, gslq/gssq (16-bytes load/store instructions) overrides the instruction format of lwc2/swc2. If we wan't to use gslq/ gssq for optimization in kernel, we should enable COP2 usage in kernel. Please pay attention that in this patch we only enable COP2 in kernel, which means it will lose ST0_CU2 when a process go to user space (try to use COP2 in user space will trigger an exception and then grab COP2, which is similar to FPU). And as a result, we need to modify the context switching code because the new scheduled process doesn't contain ST0_CU2 in its THERAD_STATUS probably. For zboot, we disable gslq/gssq be generated by toolchain. Signed-off-by: Huacai Chen Signed-off-by: Thomas Bogendoerfer

mips: Add MIPS Release 5 support

2020-05-22T07:09:01+00:00

There are five MIPS32/64 architecture releases currently available: from 1 to 6 except fourth one, which was intentionally skipped. Three of them can be called as major: 1st, 2nd and 6th, that not only have some system level alterations, but also introduced significant core/ISA level updates. The rest of the MIPS architecture releases are minor. Even though they don't have as much ISA/system/core level changes as the major ones with respect to the previous releases, they still provide a set of updates (I'd say they were intended to be the intermediate releases before a major one) that might be useful for the kernel and user-level code, when activated by the kernel or compiler. In particular the following features were introduced or ended up being available at/after MIPS32/64 Release 5 architecture: + the last release of the misaligned memory access instructions, + virtualisation - VZ ASE - is optional component of the arch, + SIMD - MSA ASE - is optional component of the arch, + DSP ASE is optional component of the arch, + CP0.Status.FR=1 for CP1.FIR.F64=1 (pure 64-bit FPU general registers) must be available if FPU is implemented, + CP1.FIR.Has2008 support is required so CP1.FCSR.{ABS2008,NAN2008} bits are available. + UFR/UNFR aliases to access CP0.Status.FR from user-space by means of ctc1/cfc1 instructions (enabled by CP0.Config5.UFR), + CP0.COnfig5.LLB=1 and eretnc instruction are implemented to without accidentally clearing LL-bit when returning from an interrupt, exception, or error trap, + XPA feature together with extended versions of CPx registers is introduced, which needs to have mfhc0/mthc0 instructions available. So due to these changes GNU GCC provides an extended instructions set support for MIPS32/64 Release 5 by default like eretnc/mfhc0/mthc0. Even though the architecture alteration isn't that big, it still worth to be taken into account by the kernel software. Finally we can't deny that some optimization/limitations might be found in future and implemented on some level in kernel or compiler. In this case having even intermediate MIPS architecture releases support would be more than useful. So the most of the changes provided by this commit can be split into either compile- or runtime configs related. The compile-time related changes are caused by adding the new CONFIG_CPU_MIPS32_R5/CONFIG_CPU_MIPSR5 configs and concern the code activating MIPSR2 or MIPSR6 already implemented features (like eretnc/LLbit, mthc0/mfhc0). In addition CPU_HAS_MSA can be now freely enabled for MIPS32/64 release 5 based platforms as this is done for CPU_MIPS32_R6 CPUs. The runtime changes concerns the features which are handled with respect to the MIPS ISA revision detected at run-time by means of CP0.Config.{AT,AR} bits. Alas these fields can be used to detect either r1 or r2 or r6 releases. But since we know which CPUs in fact support the R5 arch, we can manually set MIPS_CPU_ISA_M32R5/MIPS_CPU_ISA_M64R5 bit of c->isa_level and then use cpu_has_mips32r5/cpu_has_mips64r5 where it's appropriate. Since XPA/EVA provide too complex alterationss and to have them used with MIPS32 Release 2 charged kernels (for compatibility with current platform configs) they are left to be setup as a separate kernel configs. Co-developed-by: Alexey Malahov Signed-off-by: Alexey Malahov Signed-off-by: Serge Semin Cc: Thomas Bogendoerfer Cc: Paul Burton Cc: Ralf Baechle Cc: Arnd Bergmann Cc: Rob Herring Cc: devicetree@vger.kernel.org Signed-off-by: Thomas Bogendoerfer

MIPS: Avoid using .set mips0 to restore ISA

2018-11-09T18:23:19+00:00

We currently have 2 commonly used methods for switching ISA within assembly code, then restoring the original ISA. 1) Using a pair of .set push & .set pop directives. For example: .set push .set mips32r2 .set pop 2) Using .set mips0 to restore the ISA originally specified on the command line. For example: .set mips32r2 .set mips0 Unfortunately method 2 does not work with nanoMIPS toolchains, where the assembler rejects the .set mips0 directive like so: Error: cannot change ISA from nanoMIPS to mips0 In preparation for supporting nanoMIPS builds, switch all instances of method 2 in generic non-platform-specific code to use push & pop as in method 1 instead. The .set push & .set pop is arguably cleaner anyway, and if nothing else it's good to consistently use one method. Signed-off-by: Paul Burton Patchwork: https://patchwork.linux-mips.org/patch/21037/ Cc: linux-mips@linux-mips.org

MIPS: Fix exception entry when CONFIG_EVA enabled

2017-10-31T23:49:33+00:00

Commit 9fef68686317b ("MIPS: Make SAVE_SOME more standard") made several changes to the order in which registers are saved in the SAVE_SOME macro, used by exception handlers to save the processor state. In particular, it removed the move k1, sp in the delay slot of the branch testing if the processor is already in kernel mode. This is replaced later in the macro by a move k0, sp When CONFIG_EVA is disabled, this instruction actually appears in the delay slot of the branch. However, when CONFIG_EVA is enabled, instead the RPS workaround of MFC0 k0, CP0_ENTRYHI appears in the delay slot. This results in k0 not containing the stack pointer, but some unrelated value, which is then saved to the kernel stack. On exit from the exception, this bogus value is restored to the stack pointer, resulting in an OOPS. Fix this by moving the save of SP in k0 explicitly in the delay slot of the branch, outside of the CONFIG_EVA section, restoring the expected instruction ordering when CONFIG_EVA is active. Fixes: 9fef68686317b ("MIPS: Make SAVE_SOME more standard") Signed-off-by: Matt Redfearn Reported-by: Vladimir Kondratiev Reviewed-by: Corey Minyard Reviewed-by: James Hogan Patchwork: https://patchwork.linux-mips.org/patch/17471/ Signed-off-by: James Hogan

MIPS: Add DWARF unwinding to assembly

2017-09-06T09:01:52+00:00

This will allow kdump dumps to work correclty with MIPS and future DWARF unwinding of the stack to give accurate tracebacks. Signed-off-by: Corey Minyard Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/16990/ Signed-off-by: Ralf Baechle

MIPS: Make SAVE_SOME more standard

2017-09-06T09:01:26+00:00

Modify the SAVE_SOME macro to look more like a standard function, doing the arithmetic for the frame on the SP register instead of copying it from K1, and by saving the stored EPC from the RA. This lets the get_frame_info() function process this function like any other. It also remove an instruction or two from the kernel entry, making it more efficient. unwind_stack_by_address() has special handling for the top of the interrupt stack, but without this change unwinding will still fail if you get an interrupt while handling an interrupt and try to do a traceback from the second interrupt. This change modifies the get_saved_sp macro to optionally store the fetched value right into sp and store the old SP value into K0. Then it's just a matter of subtracting the frame from SP and storing the old SP from K0. This required changing the DADDI workaround a bit, since K0 holds the SP, we had to use K1 for AT. But it eliminated some of the special handling for the DADDI workaround. Saving the RA register was moved up to before fetching the CP0_EPC register, so the CP0_EPC register could be stored into RA and the saved. This lets the traceback code know where RA is actually stored. Signed-off-by: Corey Minyard Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/16991/ Signed-off-by: Ralf Baechle

MIPS: Remove RESTORE_ALL_AND_RET

2017-01-03T15:34:42+00:00

The RESTORE_ALL_AND_RET macro is never used. Remove the dead code. Signed-off-by: Paul Burton Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/14411/ Signed-off-by: Ralf Baechle

MIPS: Remove r2_emul_return from struct thread_info

2017-01-03T15:34:41+00:00

The r2_emul_return field in struct thread_info was used in order to take an alternate codepath when returning to userland, which (besides not implementing certain features) effectively used the eretnc instruction in place of eret. The difference is that eretnc doesn't clear LLBit, and therefore doesn't cause a linked load & store sequence to fail due to emulation like eret would. The reason eret would usually be used to clear LLBit is so that after context switching we ensure that a load performed by one task doesn't influence another task. However commit 7c151d3d5d7a ("MIPS: Make use of the ERETNC instruction on MIPS R6") which introduced the r2_emul_return field and conditional use of eretnc also for some reason began explicitly clearing LLBit during context switches - despite retaining the use of eret for everything but returns from the pre-r6 instruction emulation code. As LLBit is cleared upon context switches anyway, simplify this by using eretnc unconditionally for MIPSr6 kernels. This allows us to remove the 4 byte r2_emul_return boolean from struct thread_info, simplify the return to user code in entry.S and avoid the overhead of tracking & checking state which we don't need. Signed-off-by: Paul Burton Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/14408/ Signed-off-by: Ralf Baechle