powerpc: BookE hardware watchpoint support

This patch implements support for HW based watchpoint via the
DBSR_DAC (Data Address Compare) facility of the BookE processors.

It does so by interfacing with the existing DABR breakpoint code
and adding the necessary bits and pieces for the new bits to
be properly set or cleared

Signed-off-by: Luis Machado <luisgpm@br.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 66 insertions, 6 deletions

diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index 8feb93e7890c..a5d0e78779c8 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -703,7 +703,7 @@ void user_enable_single_step(struct task_struct *task)
 
         if (regs != NULL) {
 #if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
-                task->thread.dbcr0 = DBCR0_IDM | DBCR0_IC;
+                task->thread.dbcr0 |= DBCR0_IDM | DBCR0_IC;
                 regs->msr |= MSR_DE;
 #else
                 regs->msr |= MSR_SE;
@@ -716,9 +716,16 @@ void user_disable_single_step(struct task_struct *task)
 {
         struct pt_regs *regs = task->thread.regs;
 
+
+#if defined(CONFIG_44x) || defined(CONFIG_BOOKE)
+        /* If DAC then do not single step, skip */
+        if (task->thread.dabr)
+                return;
+#endif
+
         if (regs != NULL) {
 #if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
-                task->thread.dbcr0 = 0;
+                task->thread.dbcr0 &= ~(DBCR0_IC | DBCR0_IDM);
                 regs->msr &= ~MSR_DE;
 #else
                 regs->msr &= ~MSR_SE;
@@ -727,22 +734,75 @@ void user_disable_single_step(struct task_struct *task)
         clear_tsk_thread_flag(task, TIF_SINGLESTEP);
 }
 
-static int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
+int ptrace_set_debugreg(struct task_struct *task, unsigned long addr,
                                unsigned long data)
 {
-        /* We only support one DABR and no IABRS at the moment */
+        /* For ppc64 we support one DABR and no IABR's at the moment (ppc64).
+         *  For embedded processors we support one DAC and no IAC's at the
+         *  moment.
+         */
         if (addr > 0)
                 return -EINVAL;
 
-        /* The bottom 3 bits are flags */
         if ((data & ~0x7UL) >= TASK_SIZE)
                 return -EIO;
 
-        /* Ensure translation is on */
+#ifdef CONFIG_PPC64
+
+        /* For processors using DABR (i.e. 970), the bottom 3 bits are flags.
+         *  It was assumed, on previous implementations, that 3 bits were
+         *  passed together with the data address, fitting the design of the
+         *  DABR register, as follows:
+         *
+         *  bit 0: Read flag
+         *  bit 1: Write flag
+         *  bit 2: Breakpoint translation
+         *
+         *  Thus, we use them here as so.
+         */
+
+        /* Ensure breakpoint translation bit is set */
         if (data && !(data & DABR_TRANSLATION))
                 return -EIO;
 
+        /* Move contents to the DABR register */
         task->thread.dabr = data;
+
+#endif
+#if defined(CONFIG_44x) || defined(CONFIG_BOOKE)
+
+        /* As described above, it was assumed 3 bits were passed with the data
+         *  address, but we will assume only the mode bits will be passed
+         *  as to not cause alignment restrictions for DAC-based processors.
+         */
+
+        /* DAC's hold the whole address without any mode flags */
+        task->thread.dabr = data & ~0x3UL;
+
+        if (task->thread.dabr == 0) {
+                task->thread.dbcr0 &= ~(DBSR_DAC1R | DBSR_DAC1W | DBCR0_IDM);
+                task->thread.regs->msr &= ~MSR_DE;
+                return 0;
+        }
+
+        /* Read or Write bits must be set */
+
+        if (!(data & 0x3UL))
+                return -EINVAL;
+
+        /* Set the Internal Debugging flag (IDM bit 1) for the DBCR0
+           register */
+        task->thread.dbcr0 = DBCR0_IDM;
+
+        /* Check for write and read flags and set DBCR0
+           accordingly */
+        if (data & 0x1UL)
+                task->thread.dbcr0 |= DBSR_DAC1R;
+        if (data & 0x2UL)
+                task->thread.dbcr0 |= DBSR_DAC1W;
+
+        task->thread.regs->msr |= MSR_DE;
+#endif
         return 0;
 }