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From:   Vineet Gupta <vineet.gupta1@synopsys.com>
To:     <linux-snps-arc@lists.infradead.org>
CC:     <linux-kernel@vger.kernel.org>,
        Vineet Gupta <vineet.gupta1@synopsys.com>
Subject: [PATCH] ARCv2: support manual regfile save on interrupts
Date:   Tue, 5 Feb 2019 10:35:44 -0800
Message-ID: <1549391744-5649-1-git-send-email-vgupta@synopsys.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

There's a hardware bug which affects the HSDK platform, triggered by
micro-ops for auto-saving regfile on taken interrupt. The workaround is
to inhibit autosave.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
---
 arch/arc/Kconfig                   |  8 ++++++
 arch/arc/include/asm/entry-arcv2.h | 54 ++++++++++++++++++++++++++++++++++++++
 arch/arc/kernel/entry-arcv2.S      |  4 ++-
 arch/arc/kernel/intc-arcv2.c       |  2 ++
 arch/arc/plat-hsdk/Kconfig         |  1 +
 5 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 376366a7db81..7215f52b3413 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -407,6 +407,14 @@ config ARC_HAS_ACCL_REGS
 	  (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_IRQ_NO_AUTOSAVE
+	bool "Disable hardware autosave regfile on interrupts"
+	default n
+	help
+	  On HS cores, taken interrupt auto saves the regfile on stack.
+	  This is programmable and can be optionally disabled in which case
+	  software INTERRUPT_PROLOGUE/EPILGUE do the needed work
+
 endif	# ISA_ARCV2
 
 endmenu   # "ARC CPU Configuration"
diff --git a/arch/arc/include/asm/entry-arcv2.h b/arch/arc/include/asm/entry-arcv2.h
index 309f4e6721b3..3173d7fa4f72 100644
--- a/arch/arc/include/asm/entry-arcv2.h
+++ b/arch/arc/include/asm/entry-arcv2.h
@@ -17,6 +17,33 @@
 	;
 	; Now manually save: r12, sp, fp, gp, r25
 
+#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
+.ifnc \called_from, exception
+	st.as	r9, [sp, -10]	; save r9 is right slot
+	sub	sp, sp, 12	; skip JLI, LDI, EI
+
+	PUSH	lp_count
+	PUSHAX	lp_start
+	PUSHAX	lp_end
+	PUSH	blink
+
+	PUSH	r11
+	PUSH	r10
+
+	sub	sp, sp, 4	; skip r9
+
+	PUSH	r8
+	PUSH	r7
+	PUSH	r6
+	PUSH	r5
+	PUSH	r4
+	PUSH	r3
+	PUSH	r2
+	PUSH	r1
+	PUSH	r0
+.endif
+#endif
+
 #ifdef CONFIG_ARC_HAS_ACCL_REGS
 	PUSH	r59
 	PUSH	r58
@@ -86,6 +113,33 @@
 	POP	r59
 #endif
 
+#ifdef CONFIG_ARC_IRQ_NO_AUTOSAVE
+.ifnc \called_from, exception
+	POP	r0
+	POP	r1
+	POP	r2
+	POP	r3
+	POP	r4
+	POP	r5
+	POP	r6
+	POP	r7
+	POP	r8
+	POP	r9
+	POP	r10
+	POP	r11
+
+	POP	blink
+	POPAX	lp_end
+	POPAX	lp_start
+
+	POP	r9
+	mov	lp_count, r9
+
+	add	sp, sp, 12	; skip JLI, LDI, EI
+	ld.as	r9, [sp, -10]	; reload r9 which got clobbered
+.endif
+#endif
+
 .endm
 
 /*------------------------------------------------------------------------*/
diff --git a/arch/arc/kernel/entry-arcv2.S b/arch/arc/kernel/entry-arcv2.S
index cc558a25b8fa..562089d62d9d 100644
--- a/arch/arc/kernel/entry-arcv2.S
+++ b/arch/arc/kernel/entry-arcv2.S
@@ -209,7 +209,9 @@ restore_regs:
 ;####### Return from Intr #######
 
 debug_marker_l1:
-	bbit1.nt r0, STATUS_DE_BIT, .Lintr_ret_to_delay_slot
+	; bbit1.nt r0, STATUS_DE_BIT, .Lintr_ret_to_delay_slot
+	btst	r0, STATUS_DE_BIT		; Z flag set if bit clear
+	bnz	.Lintr_ret_to_delay_slot	; branch if STATUS_DE_BIT set
 
 .Lisr_ret_fast_path:
 	; Handle special case #1: (Entry via Exception, Return via IRQ)
diff --git a/arch/arc/kernel/intc-arcv2.c b/arch/arc/kernel/intc-arcv2.c
index 067ea362fb3e..cf18b3e5a934 100644
--- a/arch/arc/kernel/intc-arcv2.c
+++ b/arch/arc/kernel/intc-arcv2.c
@@ -49,11 +49,13 @@ void arc_init_IRQ(void)
 
 	*(unsigned int *)&ictrl = 0;
 
+#ifndef CONFIG_ARC_IRQ_NO_AUTOSAVE
 	ictrl.save_nr_gpr_pairs = 6;	/* r0 to r11 (r12 saved manually) */
 	ictrl.save_blink = 1;
 	ictrl.save_lp_regs = 1;		/* LP_COUNT, LP_START, LP_END */
 	ictrl.save_u_to_u = 0;		/* user ctxt saved on kernel stack */
 	ictrl.save_idx_regs = 1;	/* JLI, LDI, EI */
+#endif
 
 	WRITE_AUX(AUX_IRQ_CTRL, ictrl);
 
diff --git a/arch/arc/plat-hsdk/Kconfig b/arch/arc/plat-hsdk/Kconfig
index f25c085b9874..23e00216e5a5 100644
--- a/arch/arc/plat-hsdk/Kconfig
+++ b/arch/arc/plat-hsdk/Kconfig
@@ -9,6 +9,7 @@ menuconfig ARC_SOC_HSDK
 	bool "ARC HS Development Kit SOC"
 	depends on ISA_ARCV2
 	select ARC_HAS_ACCL_REGS
+	select ARC_IRQ_NO_AUTOSAVE
 	select CLK_HSDK
 	select RESET_HSDK
 	select HAVE_PCI
-- 
2.7.4