[PATCH 1/3] [v3] hvc_dcc: don't ignore errors during initialization

[PATCH 1/3] [v3] hvc_dcc: don't ignore errors during initialization

[Timur Tabi]

hvc_instantiate() and hvc_alloc() return errors if they fail, so don't
ignore them.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
---
 drivers/tty/hvc/hvc_dcc.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index 809920d..82f240f 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -70,20 +70,27 @@ static const struct hv_ops hvc_dcc_get_put_ops = {
 
 static int __init hvc_dcc_console_init(void)
 {
+	int ret;
+
 	if (!hvc_dcc_check())
 		return -ENODEV;
 
-	hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
-	return 0;
+	/* Returns -1 if error */
+	ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
+
+	return ret < 0 ? -ENODEV : 0;
 }
 console_initcall(hvc_dcc_console_init);
 
 static int __init hvc_dcc_init(void)
 {
+	struct hvc_struct *p;
+
 	if (!hvc_dcc_check())
 		return -ENODEV;
 
-	hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
-	return 0;
+	p = hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
+
+	return PTR_ERR_OR_ZERO(p);
 }
 device_initcall(hvc_dcc_init);
-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

[PATCH 2/3] [v5] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc

[Timur Tabi]

From: Abhimanyu Kapur <abhimany@codeaurora.org>

Add support for debug communications channel based
hvc console for arm64 cpus.

Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>
Signed-off-by: Timur Tabi <timur@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
index 0000000..65e0190
--- /dev/null
+++ b/arch/arm64/include/asm/dcc.h
@@ -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.
+ */
+#ifndef __ASM_DCC_H
+#define __ASM_DCC_H
+
+#include <asm/barrier.h>
+
+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));
+	isb();
+
+	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));
+	isb();
+}
+
+#endif
diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index 2509d05..574da15 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -81,7 +81,7 @@ config HVC_UDBG
 
 config HVC_DCC
        bool "ARM JTAG DCC console"
-       depends on ARM
+       depends on ARM || ARM64
        select HVC_DRIVER
        help
          This console uses the JTAG DCC on ARM to create a console under the HVC
-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

[PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC

[Timur Tabi]

If the DCC driver loads, then disable user-space access to the DCC so that
we don't have two entities trying to access the DCC at the same time.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
---
 arch/arm/include/asm/dcc.h   | 15 +++++++++++++++
 arch/arm64/include/asm/dcc.h | 11 +++++++++++
 drivers/tty/hvc/hvc_dcc.c    |  2 ++
 3 files changed, 28 insertions(+)

diff --git a/arch/arm/include/asm/dcc.h b/arch/arm/include/asm/dcc.h
index b74899d..c50056b 100644
--- a/arch/arm/include/asm/dcc.h
+++ b/arch/arm/include/asm/dcc.h
@@ -9,8 +9,11 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  */
+#ifndef __ASM_DCC_H
+#define __ASM_DCC_H
 
 #include <asm/barrier.h>
+#include <asm/hardware/cp14.h>
 
 static inline u32 __dcc_getstatus(void)
 {
@@ -39,3 +42,15 @@ static inline void __dcc_putchar(char c)
 		: "r" (c));
 	isb();
 }
+
+static inline void __dcc_initialize(void)
+{
+	u32 val;
+
+	/* Disable user-space access to DCC */
+	val = MRC14(0, c0, c1, 0);
+	val |= 1 << 12; /* DSCR[Comms] */
+	MCR14(val, 0, c0, c1, 0);
+}
+
+#endif
diff --git a/arch/arm64/include/asm/dcc.h b/arch/arm64/include/asm/dcc.h
index 65e0190..cff9512 100644
--- a/arch/arm64/include/asm/dcc.h
+++ b/arch/arm64/include/asm/dcc.h
@@ -52,4 +52,15 @@ static inline void __dcc_putchar(char c)
 	isb();
 }
 
+static inline void __dcc_initialize(void)
+{
+	u32 val;
+
+	/* Disable user-space access to DCC */
+	asm volatile ("mrs %0, mdscr_el1\n"
+		"	orr %0, %0, #4096\n" /* Set the TDCC bit */
+		"	msr mdscr_el1, %0\n"
+		: "=r" (val));
+}
+
 #endif
diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index 82f240f..14d4a473 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -75,6 +75,8 @@ static int __init hvc_dcc_console_init(void)
 	if (!hvc_dcc_check())
 		return -ENODEV;
 
+	__dcc_initialize();
+
 	/* Returns -1 if error */
 	ret = hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
 
-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

[PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC

[Will Deacon]

On Thu, Aug 20, 2015 at 12:02:50AM +0100, Timur Tabi wrote:
> If the DCC driver loads, then disable user-space access to the DCC so that
> we don't have two entities trying to access the DCC at the same time.

In the interests of making some headway with this, just drop this patch
and I'll queue the diff below via the arm64 tree.

Will

--->8

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 39139a3aa16d..4c922ecce600 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -156,7 +156,7 @@ ENTRY(__cpu_setup)
 
 	mov	x0, #3 << 20
 	msr	cpacr_el1, x0			// Enable FP/ASIMD
-	msr	mdscr_el1, xzr			// Reset mdscr_el1
+	msr	mdscr_el1, #1 << 12		// Reset mdscr_el1
 	/*
 	 * Memory region attributes for LPAE:
 	 *

[PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC

[Catalin Marinas]

On Thu, Aug 20, 2015 at 11:46:45AM +0100, Will Deacon wrote:
> On Thu, Aug 20, 2015 at 12:02:50AM +0100, Timur Tabi wrote:
> > If the DCC driver loads, then disable user-space access to the DCC so that
> > we don't have two entities trying to access the DCC at the same time.
> 
> In the interests of making some headway with this, just drop this patch
> and I'll queue the diff below via the arm64 tree.
> 
> Will
> 
> --->8
> 
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 39139a3aa16d..4c922ecce600 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -156,7 +156,7 @@ ENTRY(__cpu_setup)
>  
>  	mov	x0, #3 << 20
>  	msr	cpacr_el1, x0			// Enable FP/ASIMD
> -	msr	mdscr_el1, xzr			// Reset mdscr_el1
> +	msr	mdscr_el1, #1 << 12		// Reset mdscr_el1

Nitpick: expand the "Reset..." comment to include some text about this
bit.

-- 
Catalin

[PATCH 3/3] [v2] hvc_dcc: disable user-space access to DCC

[Timur Tabi]

On 08/20/2015 05:46 AM, Will Deacon wrote:
>> If the DCC driver loads, then disable user-space access to the DCC so that
>> >we don't have two entities trying to access the DCC at the same time.

> In the interests of making some headway with this, just drop this patch
> and I'll queue the diff below via the arm64 tree.

Yes, that would be great.  Thank you.

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.