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>

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 7124ab8..55432a8 100644 (file)
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -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

diff --git a/arch/arc/include/asm/arcregs.h b/arch/arc/include/asm/arcregs.h
index f7e4324..135f6ec 100644 (file)
--- a/arch/arc/include/asm/arcregs.h
+++ b/arch/arc/include/asm/arcregs.h
@@ -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>

diff --git a/arch/arc/include/asm/dsp-impl.h b/arch/arc/include/asm/dsp-impl.h
new file mode 100644 (file)
index 0000000..6066203
--- /dev/null
+++ b/arch/arc/include/asm/dsp-impl.h
@@ -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 */

diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
index 0b8b63d..dd6aa18 100644 (file)
--- 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 r10, r11 registers pair */
+       DSP_SAVE_REGFILE_IRQ
 .endm
 
 /*------------------------------------------------------------------------*/

diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
index 6f41265..6eb23f1 100644 (file)
--- 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 820c0cf..1ed1528 100644 (file)
--- a/arch/arc/kernel/setup.c
+++ b/arch/arc/kernel/setup.c
@@ -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();
        }
 }