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Subject[PATCH 4/4] hvc_dcc: disable user-space access to DCC
Date
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 fcb8d7d..7843e62 100644
--- a/arch/arm64/include/asm/dcc.h
+++ b/arch/arm64/include/asm/dcc.h
@@ -49,4 +49,15 @@ static inline void __dcc_putchar(char c)
isb();
}

+static inline void __dcc_initialize(void)
+{
+ u32 val;
+
+ /* Disable user-space access to DCC */
+ asm ("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 f8b8cf2..5ccafa4 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c
@@ -231,6 +231,8 @@ 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.


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