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>

1 files changed, 54 insertions, 0 deletions

diff --git a/arch/arc/include/asm/dsp-impl.h b/arch/arc/include/asm/dsp-impl.h
new file mode 100644
index 000000000000..606620383eca
--- /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 */