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Re: [PATCH v7] MIPS: micromips: Fix improper definition of ISA exception

To: "Steven J. Hill" <Steven.Hill@imgtec.com>
Subject: Re: [PATCH v7] MIPS: micromips: Fix improper definition of ISA exception bit.
From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Date: Thu, 06 Jun 2013 01:27:04 +0400
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org
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On 06/06/2013 01:13 AM, Steven J. Hill wrote:
The ISA exception bit selects whether exceptions are taken in classic
or microMIPS mode. This bit is Config3.ISAOnExc and was improperly
defined as bits 16 and 17 instead of just bit 16. A new function was
added so that platforms could set this bit when running a kernel
compiled with only microMIPS instructions.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
Acked-by: David Daney <david.daney@cavium.com>
---
Changes from v6:
* Add '#ifdef SYS_SUPPORTS_MICROMIPS' around body of
   'set_micromips_exception_mode' function. Platforms that
   do not support microMIPS will optimize it out.

  arch/mips/include/asm/mipsregs.h |   20 +++++++++++++++++++-
  arch/mips/kernel/cpu-probe.c     |    3 ---
  arch/mips/kernel/traps.c         |    5 +++++
  3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h
index 87e6207..0a9544a 100644
--- a/arch/mips/include/asm/mipsregs.h
+++ b/arch/mips/include/asm/mipsregs.h
@@ -596,7 +596,7 @@
  #define MIPS_CONF3_RXI                (_ULCAST_(1) << 12)
  #define MIPS_CONF3_ULRI               (_ULCAST_(1) << 13)
  #define MIPS_CONF3_ISA                (_ULCAST_(3) << 14)
-#define MIPS_CONF3_ISA_OE      (_ULCAST_(3) << 16)
+#define MIPS_CONF3_ISA_OE      (_ULCAST_(1) << 16)
  #define MIPS_CONF3_VZ         (_ULCAST_(1) << 23)
#define MIPS_CONF4_MMUSIZEEXT (_ULCAST_(255) << 0)
@@ -1161,6 +1161,24 @@ do {                                                     
                \
  #define write_c0_brcm_sleepcount(val) __write_32bit_c0_register($22, 7, val)
/*
+ * Set exceptions to be taken in microMIPS mode only, otherwise
+ * set for classic exceptions.
+ */
+static inline void set_micromips_exception_mode(void)
+{
+#ifdef SYS_SUPPORTS_MICROMIPS
+       unsigned int config3 = read_c0_config3();
+
+#ifdef CONFIG_CPU_MICROMIPS
+       if (config3 & MIPS_CONF3_ISA)
+               write_c0_config3(config3 | MIPS_CONF3_ISA_OE);
+       else
+#endif
+               write_c0_config3(config3 & ~MIPS_CONF3_ISA_OE);
+#endif

Let me remind that #ifdef's inside the function body are considered ugly and should be avoided if at all possible (by defining an empty implementation in the
#else branch).

WBR, Sergei


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