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    Subject[PATCH 3/5] ARC: handle DSP presence in HW
    Date
    In case of DSP extension presence in HW some instructions
    (related to integer multiply, multiply-accumulate, and divide
    operation) executes on this DSP execution unit. So their
    execution will depend on dsp configuration register (DSP_CTRL)

    As we want these instructions to execute the same way regardless
    of DSP presence we need to set DSP_CTRL properly. However this
    register can be modified bu any usersace app therefore any
    usersace may break kernel execution.

    Fix that by configure DSP_CTRL in CPU early code and in IRQs
    entries.

    Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
    ---
    arch/arc/Kconfig | 25 ++++++++++++++++-
    arch/arc/include/asm/arcregs.h | 12 ++++++++
    arch/arc/include/asm/dsp-impl.h | 45 ++++++++++++++++++++++++++++++
    arch/arc/include/asm/entry-arcv2.h | 3 ++
    arch/arc/kernel/head.S | 4 +++
    arch/arc/kernel/setup.c | 4 +++
    6 files changed, 92 insertions(+), 1 deletion(-)
    create mode 100644 arch/arc/include/asm/dsp-impl.h

    diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
    index 8383155c8c82..b9cd7ce3f878 100644
    --- a/arch/arc/Kconfig
    +++ b/arch/arc/Kconfig
    @@ -404,13 +404,36 @@ config ARC_HAS_DIV_REM
    default y

    config ARC_HAS_ACCL_REGS
    - bool "Reg Pair ACCL:ACCH (FPU and/or MPY > 6)"
    + bool "Reg Pair ACCL:ACCH (FPU and/or MPY > 6 and/or DSP)"
    default y
    help
    Depending on the configuration, CPU can contain accumulator reg-pair
    (also referred to as r58:r59). These can also be used by gcc as GPR so
    kernel needs to save/restore per process

    +choice
    + prompt "DSP support"
    + default ARC_NO_DSP
    + help
    + Depending on the configuration, CPU can contain DSP registers
    + (ACC0_GLO, ACC0_GHI, DSP_BFLY0, DSP_CTRL, DSP_FFT_CTRL).
    + Bellow is options describing how to handle these registers in
    + interrupt entry / exit and in context switch.
    +
    +config ARC_NO_DSP
    + bool "No DSP extension presence in HW"
    + help
    + No DSP extension presence in HW
    +
    +config ARC_DSP_KERNEL
    + bool "DSP extension in HW, no support for userspace"
    + select ARC_HAS_ACCL_REGS
    + help
    + DSP extension presence in HW, no support for DSP-enabled userspace
    + applications. We don't save / restore DSP registers and only do
    + some minimal preparations so userspace won't be able to break kernel
    +endchoice
    +
    config ARC_IRQ_NO_AUTOSAVE
    bool "Disable hardware autosave regfile on interrupts"
    default n
    diff --git a/arch/arc/include/asm/arcregs.h b/arch/arc/include/asm/arcregs.h
    index 5134f0baf33c..0004b1e9b325 100644
    --- a/arch/arc/include/asm/arcregs.h
    +++ b/arch/arc/include/asm/arcregs.h
    @@ -116,6 +116,18 @@
    #define ARC_AUX_DPFP_2H 0x304
    #define ARC_AUX_DPFP_STAT 0x305

    +/*
    + * DSP-related registers
    + */
    +#define ARC_AUX_DSP_BUILD 0x7A
    +#define ARC_AUX_ACC0_LO 0x580
    +#define ARC_AUX_ACC0_GLO 0x581
    +#define ARC_AUX_ACC0_HI 0x582
    +#define ARC_AUX_ACC0_GHI 0x583
    +#define ARC_AUX_DSP_BFLY0 0x598
    +#define ARC_AUX_DSP_CTRL 0x59F
    +#define ARC_AUX_DSP_FFT_CTRL 0x59E
    +
    #ifndef __ASSEMBLY__

    #include <soc/arc/aux.h>
    diff --git a/arch/arc/include/asm/dsp-impl.h b/arch/arc/include/asm/dsp-impl.h
    new file mode 100644
    index 000000000000..788093cbe689
    --- /dev/null
    +++ b/arch/arc/include/asm/dsp-impl.h
    @@ -0,0 +1,45 @@
    +/* SPDX-License-Identifier: GPL-2.0-only */
    +/*
    + * Copyright (C) 2020 Synopsys, Inc. (www.synopsys.com)
    + *
    + * Author: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
    + */
    +#ifndef __ASM_ARC_DSP_IMPL_H
    +#define __ASM_ARC_DSP_IMPL_H
    +
    +#define DSP_CTRL_DISABLED_ALL 0
    +
    +#ifdef __ASSEMBLY__
    +
    +/* clobbers r5 register */
    +.macro DSP_EARLY_INIT
    + lr r5, [ARC_AUX_DSP_BUILD]
    + bmsk r5, r5, 7
    + breq r5, 0, 1f
    + mov r5, DSP_CTRL_DISABLED_ALL
    + sr r5, [ARC_AUX_DSP_CTRL]
    +1:
    +.endm
    +
    +/* clobbers r58, r59 registers pair */
    +.macro DSP_SAVE_REGFILE_IRQ
    +#if defined(CONFIG_ARC_DSP_KERNEL)
    + /* Drop any changes to DSP_CTRL made by userspace so userspace won't be
    + * able to break kernel */
    + mov r58, DSP_CTRL_DISABLED_ALL
    + sr r58, [ARC_AUX_DSP_CTRL]
    +#endif /* ARC_DSP_KERNEL */
    +.endm
    +
    +#else /* __ASEMBLY__ */
    +
    +static inline bool dsp_exist(void)
    +{
    + struct bcr_generic bcr;
    +
    + READ_BCR(ARC_AUX_DSP_BUILD, bcr);
    + return !!bcr.ver;
    +}
    +
    +#endif /* __ASEMBLY__ */
    +#endif /* __ASM_ARC_DSP_IMPL_H */
    diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
    index 0b8b63d0bec1..e3f8bd3e2eba 100644
    --- a/arch/arc/include/asm/entry-arcv2.h
    +++ b/arch/arc/include/asm/entry-arcv2.h
    @@ -4,6 +4,7 @@
    #define __ASM_ARC_ENTRY_ARCV2_H

    #include <asm/asm-offsets.h>
    +#include <asm/dsp-impl.h>
    #include <asm/irqflags-arcv2.h>
    #include <asm/thread_info.h> /* For THREAD_SIZE */

    @@ -165,6 +166,8 @@
    ST2 r58, r59, PT_r58
    #endif

    + /* clobbers r58, r59 registers pair, so must be after r58, r59 save */
    + DSP_SAVE_REGFILE_IRQ
    .endm

    /*------------------------------------------------------------------------*/
    diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
    index 6f41265f6250..6eb23f1545ee 100644
    --- a/arch/arc/kernel/head.S
    +++ b/arch/arc/kernel/head.S
    @@ -14,6 +14,7 @@
    #include <asm/entry.h>
    #include <asm/arcregs.h>
    #include <asm/cache.h>
    +#include <asm/dsp-impl.h>
    #include <asm/irqflags.h>

    .macro CPU_EARLY_SETUP
    @@ -59,6 +60,9 @@
    #endif
    kflag r5
    #endif
    + ; Config DSP_CTRL properly, so kernel may use integer multiply,
    + ; multiply-accumulate, and divide operations
    + DSP_EARLY_INIT
    .endm

    .section .init.text, "ax",@progbits
    diff --git a/arch/arc/kernel/setup.c b/arch/arc/kernel/setup.c
    index edb55b6ee278..b3995dd673d9 100644
    --- a/arch/arc/kernel/setup.c
    +++ b/arch/arc/kernel/setup.c
    @@ -26,6 +26,7 @@
    #include <asm/unwind.h>
    #include <asm/mach_desc.h>
    #include <asm/smp.h>
    +#include <asm/dsp-impl.h>

    #define FIX_PTR(x) __asm__ __volatile__(";" : "+r"(x))

    @@ -444,6 +445,9 @@ static void arc_chk_core_config(void)
    /* Accumulator Low:High pair (r58:59) present if DSP MPY or FPU */
    present = cpu->extn_mpy.dsp | cpu->extn.fpu_sp | cpu->extn.fpu_dp;
    CHK_OPT_STRICT(CONFIG_ARC_HAS_ACCL_REGS, present);
    +
    + present = dsp_exist();
    + CHK_OPT_STRICT(CONFIG_ARC_DSP_KERNEL, present);
    }
    }

    --
    2.21.0
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