[PARISC] Document some register usages in assembly files

Document clobbers and args in entry.S and syscall.S.

entry.S: Add comment to indicate that cr27 may recycle and EDEADLOCK
detection is not 100% correct. Since this is only enabled when using
ENABLE_LWS_DEBUG, the user is warned by the comment.

Signed-off-by: Carlos O'Donell <carlos@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

2 files changed, 3 insertions, 1 deletions

diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index c7e66ee5b083..9af4b22a6d77 100644
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -1846,6 +1846,7 @@ sys_clone_wrapper:
         ldo     -16(%r30),%r29          /* Reference param save area */
 #endif
 
+        /* WARNING - Clobbers r19 and r21, userspace must save these! */
         STREG   %r2,PT_GR19(%r1)        /* save for child */
         STREG   %r30,PT_GR21(%r1)
         BL      sys_clone,%r2
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index b29b76b42bb7..d66163492890 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -164,7 +164,7 @@ linux_gateway_entry:
 #endif
         STREG   %r2,  TASK_PT_GR30(%r1)         /* ... and save it */
         
-        STREG   %r20, TASK_PT_GR20(%r1)
+        STREG   %r20, TASK_PT_GR20(%r1)         /* Syscall number */
         STREG   %r21, TASK_PT_GR21(%r1)
         STREG   %r22, TASK_PT_GR22(%r1)
         STREG   %r23, TASK_PT_GR23(%r1)         /* 4th argument */
@@ -527,6 +527,7 @@ lws_compare_and_swap:
                 We *must* giveup this call and fail.
         */
         ldw     4(%sr2,%r20), %r28                      /* Load thread register */
+        /* WARNING: If cr27 cycles to the same value we have problems */
         mfctl   %cr27, %r21                             /* Get current thread register */
         cmpb,<>,n       %r21, %r28, cas_lock            /* Called recursive? */
         b       lws_exit                                /* Return error! */