[PATCH 2/3] [v5] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc
timur at codeaurora.org
Wed Aug 19 16:02:49 PDT 2015
From: Abhimanyu Kapur <abhimany at codeaurora.org>
Add support for debug communications channel based
hvc console for arm64 cpus.
Signed-off-by: Abhimanyu Kapur <abhimany at codeaurora.org>
Signed-off-by: Timur Tabi <timur at codeaurora.org>
arch/arm64/include/asm/dcc.h | 55 ++++++++++++++++++++++++++++++++++++++++++++
drivers/tty/hvc/Kconfig | 2 +-
2 files changed, 56 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/include/asm/dcc.h
diff --git a/arch/arm64/include/asm/dcc.h b/arch/arm64/include/asm/dcc.h
new file mode 100644
@@ -0,0 +1,55 @@
+/* Copyright (c) 2014-2015 The Linux Foundation. All rights reserved.
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ * A call to __dcc_getchar() or __dcc_putchar() is typically followed by
+ * a call to __dcc_getstatus(). We want to make sure that the CPU does
+ * not speculative read the DCC status before executing the read or write
+ * instruction. That's what the ISBs are for.
+ * The 'volatile' ensures that the compiler does not cache the status bits,
+ * and instead reads the DCC register every time.
+static inline u32 __dcc_getstatus(void)
+ u32 ret;
+ asm volatile("mrs %0, mdccsr_el0" : "=r" (ret));
+ return ret;
+static inline char __dcc_getchar(void)
+ char c;
+ asm volatile("mrs %0, dbgdtrrx_el0" : "=r" (c));
+ return c;
+static inline void __dcc_putchar(char c)
+ * The typecast is to make absolutely certain that 'c' is
+ * zero-extended.
+ asm volatile("msr dbgdtrtx_el0, %0"
+ : : "r" ((unsigned long)(unsigned char)c));
diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index 2509d05..574da15 100644
@@ -81,7 +81,7 @@ config HVC_UDBG
bool "ARM JTAG DCC console"
- depends on ARM
+ depends on ARM || ARM64
This console uses the JTAG DCC on ARM to create a console under the HVC
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