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45c7328c0b
Travis' and Gelas' TRMs tell us to disable SME (set PSTATE.{ZA, SM} to
0) when we're attempting to power down. What they don't tell us is that
if this isn't done, the powerdown request will be rejected. On the
CPU_OFF path that's not a problem - we can force SVCR to 0 and be
certain the core will power off.
On the suspend to powerdown path, however, we cannot do this. The TRM
also tells us that the sequence could also be aborted on eg. GIC
interrupts. If this were to happen when we have overwritten SVCR to 0,
upon a return to the caller they would experience a loss of context. We
know that at least Linux may call into PSCI with SVCR != 0. One option
is to save the entire SME context which would be quite expensive just to
work around. Another option is to downgrade the request to a normal
suspend when SME was left on. This option is better as this is expected
to happen rarely enough to ignore the wasted power and we don't want to
burden the generic (correct) path with needless context management.
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I698fa8490ebf51461f6aa8bba84f9827c5c46ad4
56 lines
1.4 KiB
ArmAsm
56 lines
1.4 KiB
ArmAsm
/*
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* Copyright (c) 2024, Arm Limited. All rights reserved.
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <arch.h>
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#include <asm_macros.S>
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#include <common/bl_common.h>
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#include <cortex_alto.h>
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#include <cpu_macros.S>
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#include <plat_macros.S>
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/* Hardware handled coherency */
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#if HW_ASSISTED_COHERENCY == 0
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#error "Alto must be compiled with HW_ASSISTED_COHERENCY enabled"
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#endif
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/* 64-bit only core */
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#if CTX_INCLUDE_AARCH32_REGS == 1
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#error "Alto supports only AArch64. Compile with CTX_INCLUDE_AARCH32_REGS=0"
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#endif
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#if ERRATA_SME_POWER_DOWN == 0
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#error "Travis needs ERRATA_SME_POWER_DOWN=1 to powerdown correctly"
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#endif
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cpu_reset_func_start cortex_alto
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/* Disable speculative loads */
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msr SSBS, xzr
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cpu_reset_func_end cortex_alto
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func cortex_alto_core_pwr_dwn
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/* ---------------------------------------------------
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* Enable CPU power down bit in power control register
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* ---------------------------------------------------
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*/
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sysreg_bit_set CORTEX_ALTO_IMP_CPUPWRCTLR_EL1, \
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CORTEX_ALTO_IMP_CPUPWRCTLR_EL1_CORE_PWRDN_EN_BIT
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isb
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ret
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endfunc cortex_alto_core_pwr_dwn
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.section .rodata.cortex_alto_regs, "aS"
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cortex_alto_regs: /* The ASCII list of register names to be reported */
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.asciz "cpuectlr_el1", ""
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func cortex_alto_cpu_reg_dump
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adr x6, cortex_alto_regs
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mrs x8, CORTEX_ALTO_IMP_CPUECTLR_EL1
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ret
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endfunc cortex_alto_cpu_reg_dump
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declare_cpu_ops cortex_alto, CORTEX_ALTO_MIDR, \
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cortex_alto_reset_func, \
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cortex_alto_core_pwr_dwn
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