ARC: handle DSP presence in HW

When DSP extensions are present, some of the regular integer instructions
such as DIV, MACD etc are executed in the DSP unit with semantics alterable
by flags in DSP_CTRL aux register. This register is writable by userspace
and thus can potentially affect corresponding instructions in kernel code,
intentionally or otherwise. So safegaurd kernel by effectively disabling
DSP_CTRL upon bootup and every entry to kernel.

Do note that for this config we simply zero out the DSP_CTRL reg assuming
userspace doesn't really care about DSP. The next patch caters to the DSP
aware userspace where this reg is saved/restored upon kernel entry/exit.

Reviewed-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Eugeniy Paltsev 2020-03-05 23:02:50 +03:00 committed by Vineet Gupta
parent 240c84b1c2
commit 4827d0cf74
6 changed files with 104 additions and 1 deletions

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@ -401,13 +401,40 @@ 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
config ARC_DSP_HANDLED
def_bool n
choice
prompt "DSP support"
default ARC_DSP_NONE
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_DSP_NONE
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
select ARC_DSP_HANDLED
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

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@ -118,6 +118,18 @@
#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>

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@ -0,0 +1,54 @@
/* 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 r10, r11 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 - reset it to DSP_CTRL_DISABLED_ALL value
*/
mov r10, DSP_CTRL_DISABLED_ALL
sr r10, [ARC_AUX_DSP_CTRL]
#endif /* ARC_DSP_KERNEL */
.endm
#else /* __ASEMBLY__ */
#include <asm/asserts.h>
static inline bool dsp_exist(void)
{
struct bcr_generic bcr;
READ_BCR(ARC_AUX_DSP_BUILD, bcr);
return !!bcr.ver;
}
static inline void dsp_config_check(void)
{
CHK_OPT_STRICT(CONFIG_ARC_DSP_HANDLED, dsp_exist());
}
#endif /* __ASEMBLY__ */
#endif /* __ASM_ARC_DSP_IMPL_H */

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@ -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 r10, r11 registers pair */
DSP_SAVE_REGFILE_IRQ
.endm
/*------------------------------------------------------------------------*/

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@ -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

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@ -27,6 +27,7 @@
#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))
@ -440,6 +441,8 @@ 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);
dsp_config_check();
}
}