linux-kernel - [PATCH 4/4] ARCv2: smp-boot: MCIP: use Inter-Core-Debug unit to kick start non master cpus

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Date:   Mon, 16 Jan 2017 12:57:57 -0800
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     <linux-snps-arc@...ts.infradead.org>, <Alexey.Brodkin@...opsys.com>
CC:     <linux-kernel@...r.kernel.org>,
        Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [PATCH 4/4] ARCv2: smp-boot: MCIP: use Inter-Core-Debug unit to kick start non master cpus

This essentially converts a run-on-reset to halt-on-reset - so non
masters self halt in early boot code. And later they are resumed from
halted PC using MCIP ICD assist.

As mentioned in prev commits, this paves way for radio silence on
coherency unit, while master is setting up IOC and such.

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/include/asm/mcip.h |  1 +
 arch/arc/kernel/mcip.c      | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/arc/include/asm/mcip.h b/arch/arc/include/asm/mcip.h
index c8fbe4114bad..a6ae4363c388 100644
--- a/arch/arc/include/asm/mcip.h
+++ b/arch/arc/include/asm/mcip.h
@@ -36,6 +36,7 @@ struct mcip_cmd {
 #define CMD_SEMA_CLAIM_AND_READ		0x11
 #define CMD_SEMA_RELEASE		0x12
 
+#define CMD_DEBUG_RUN			0x33
 #define CMD_DEBUG_SET_MASK		0x34
 #define CMD_DEBUG_SET_SELECT		0x36
 
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index 933382e0edd0..0a1822d2fe52 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -103,12 +103,43 @@ static void mcip_probe_n_setup(void)
 	cpuinfo_arc700[0].extn.gfrc = mp.gfrc;
 }
 
+static void __init mcip_cpu_wait(int cpu)
+{
+	struct mcip_bcr mp;
+
+	READ_BCR(ARC_REG_MCIP_BCR, mp);
+
+	/*
+	 * self halt for waiting as Master will resume us using MCIP ICD assist
+	 * Note: if ICD is not configured, we are hosed, but panic here is
+	 *       not going to help as UART access might not even work
+	 */
+	if (mp.dbg)
+		asm volatile("flag 1	\n");
+}
+
+static void __init mcip_cpu_kick(int cpu, unsigned long pc)
+{
+	struct mcip_bcr mp;
+
+	READ_BCR(ARC_REG_MCIP_BCR, mp);
+
+	if (mp.dbg)
+		__mcip_cmd_data(CMD_DEBUG_RUN, 0, (1 << cpu));
+	else
+		panic("SMP boot issues: MCIP lacks ICD\n");
+}
+
 struct plat_smp_ops plat_smp_ops = {
 	.info		= smp_cpuinfo_buf,
 	.init_early_smp	= mcip_probe_n_setup,
 	.init_per_cpu	= mcip_setup_per_cpu,
 	.ipi_send	= mcip_ipi_send,
 	.ipi_clear	= mcip_ipi_clear,
+	.cpu_kick	= mcip_cpu_kick,
+#ifndef CONFIG_ARC_SMP_HALT_ON_RESET
+	.cpu_wait	= mcip_cpu_wait,
+#endif
 };
 
 #endif
-- 
2.7.4