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The indirect CSR requires multiple instructions to read/write CSR. Add a few helper macros for ease of usage. These have to be macros rather than functions. csr_read()/csr_write() stringify their CSR argument into the inline asm template via __ASM_STR(), so the CSR number must be a literal token; passing it as a function parameter emits "csrr %0, iregcsr", which the assembler rejects with "unknown CSR `iregcsr'". The stringification happens in the preprocessor, before inlining or constant propagation, so it cannot be worked around by forcing inlining or by only ever passing constants - gcc 12, gcc 16 and clang 22 all reject it alike. Underneath, csrr/csrw encode the CSR as a 12-bit immediate and RISC-V has no register-indirect form, which is also why asm/csr.h keeps every one of its accessors as a macro. Signed-off-by: Atish Patra <atishp@rivosinc.com> Reviewed-by: Charlie Jenkins <thecharlesjenkins@gmail.com> Tested-by: Charlie Jenkins <thecharlesjenkins@gmail.com> [pjw@kernel.org: expand "ind" abbreviation] Link: https://patch.msgid.link/20260807-counter_delegation-v9-5-58658104e487@meta.com Signed-off-by: Paul Walmsley <pjw@kernel.org>
51 lines
1.6 KiB
C
51 lines
1.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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#ifndef _ASM_RISCV_CSR_INDIRECT_H
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#define _ASM_RISCV_CSR_INDIRECT_H
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#include <linux/irqflags.h>
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#include <asm/csr.h>
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/*
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* These have to be macros rather than functions: csr_read()/csr_write()
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* stringify their CSR argument into the inline asm template via __ASM_STR(),
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* so the CSR number must be a literal token at preprocessing time. Passing it
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* as a function parameter emits "csrr %0, iregcsr", which no assembler can
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* resolve. RISC-V has no register-indirect form of csrr/csrw - the CSR is a
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* 12-bit immediate - so the sireg CSR selecting the indirect window cannot
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* itself be a variable.
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*/
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#define csr_indirect_read(iregcsr, iselbase, iseloff) ({ \
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unsigned long __value = 0; \
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unsigned long __flags; \
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local_irq_save(__flags); \
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csr_write(CSR_ISELECT, (iselbase) + (iseloff)); \
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__value = csr_read(iregcsr); \
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local_irq_restore(__flags); \
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__value; \
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})
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#define csr_indirect_write(iregcsr, iselbase, iseloff, value) ({ \
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unsigned long __flags; \
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local_irq_save(__flags); \
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csr_write(CSR_ISELECT, (iselbase) + (iseloff)); \
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csr_write(iregcsr, (value)); \
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local_irq_restore(__flags); \
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})
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#define csr_indirect_warl(iregcsr, iselbase, iseloff, warl_val) ({ \
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unsigned long __old_val = 0, __value = 0; \
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unsigned long __flags; \
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local_irq_save(__flags); \
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csr_write(CSR_ISELECT, (iselbase) + (iseloff)); \
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__old_val = csr_read(iregcsr); \
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csr_write(iregcsr, (warl_val)); \
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__value = csr_read(iregcsr); \
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csr_write(iregcsr, __old_val); \
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local_irq_restore(__flags); \
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__value; \
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})
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#endif
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