Commit 4827d0cf authored by Eugeniy Paltsev's avatar Eugeniy Paltsev Committed by Vineet Gupta
Browse files

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: default avatarVineet Gupta <vgupta@synopsys.com>
Signed-off-by: default avatarEugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent 240c84b1

arch/arc/Kconfig

+28 −1
Original line number Diff line number Diff line
@@ -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

arch/arc/include/asm/arcregs.h

+12 −0
Original line number Diff line number Diff line
@@ -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>

arch/arc/include/asm/dsp-impl.h

0 → 100644
+54 −0
Original line number Diff line number Diff line 
/* 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 */

arch/arc/include/asm/entry-arcv2.h

+3 −0
Original line number Diff line number Diff line
@@ -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



/*------------------------------------------------------------------------*/

arch/arc/kernel/head.S

+4 −0
Original line number Diff line number Diff line
@@ -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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