From e3f54ecdd9d266607afd7d8b62960b2154b63e9d Mon Sep 17 00:00:00 2001
From: Thomas Hellstrom <thomas-at-tungstengraphics-dot-com>
Date: Tue, 5 Sep 2006 19:36:45 +0200
Subject: Multithreaded application note.

---
 libdrm/xf86drm.c | 26 +++-----------------------
 libdrm/xf86mm.h  | 13 +++++++++++++
 2 files changed, 16 insertions(+), 23 deletions(-)

(limited to 'libdrm')

diff --git a/libdrm/xf86drm.c b/libdrm/xf86drm.c
index 6d087427..dd97e26e 100644
--- a/libdrm/xf86drm.c
+++ b/libdrm/xf86drm.c
@@ -2750,17 +2750,6 @@ int drmBOMap(int fd, drmBO *buf, unsigned mapFlags, unsigned mapHint,
     drm_bo_arg_reply_t *rep = &arg.rep;
     int ret = 0;
 
-    /*
-     * At the moment, we don't allow recursive mapping of a buffer, since
-     * the first mapping may have to be unmapped before this one to succeed.
-     * This might result in a deadlock. We need a DRM mutex mechanism!!
-     */
-
-    if (buf->mapCount) {
-	drmMsg("Recursive mapping is currently not allowed.\n");
-	return -EAGAIN;
-    }
-
     /*
      * Make sure we have a virtual address of the buffer.
      */
@@ -2827,8 +2816,6 @@ int drmBOUnmap(int fd, drmBO *buf)
     if (rep->ret)
 	return rep->ret;
 
-    --buf->mapCount;
-
     return 0;
 }
     
@@ -2840,11 +2827,6 @@ int drmBOValidate(int fd, drmBO *buf, unsigned flags, unsigned mask,
     drm_bo_arg_reply_t *rep = &arg.rep;
     int ret = 0;
 
-    if (buf->mapCount) {
-	drmMsg("Cannot validate while buffer is mapped.\n");
-	return -EAGAIN;
-    }
-
     arg.handled = 0;
     req->handle = buf->handle;
     req->mask = flags;
@@ -2853,10 +2835,12 @@ int drmBOValidate(int fd, drmBO *buf, unsigned flags, unsigned mask,
     req->op = drm_bo_validate;
     req->next = 0;
 
+
     do{
 	ret = ioctl(fd, DRM_IOCTL_BUFOBJ, &arg);
     } while (ret && errno == -EAGAIN);
     
+
     if (ret) 
 	return ret;
     if (!arg.handled)
@@ -3008,11 +2992,6 @@ int drmBOValidateList(int fd, drmBOList *list)
       if (prevNext)
 	  *prevNext = (unsigned long) arg;
 
-      if (node->buf->mapCount) {
-	  drmMsg("Cannot validate while buffer is mapped.\n");
-	  return -EAGAIN;
-      }
-
       req->next = 0;
       prevNext = &req->next;
       arg->handled = 0;
@@ -3030,6 +3009,7 @@ int drmBOValidateList(int fd, drmBOList *list)
       ret = ioctl(fd, DRM_IOCTL_BUFOBJ, &arg);
   } while (ret && errno == -EAGAIN);
 
+
   if (ret)
       return -errno;
   
diff --git a/libdrm/xf86mm.h b/libdrm/xf86mm.h
index 623f4d58..43ea71b8 100644
--- a/libdrm/xf86mm.h
+++ b/libdrm/xf86mm.h
@@ -31,6 +31,18 @@
 #include <stddef.h>
 #include "drm.h"
 
+/*
+ * Note on multithreaded applications using this interface.
+ * Libdrm is not threadsafe, so common buffer, TTM, and fence objects need to
+ * be protected using an external mutex.
+ *
+ * Note: Don't protect the following functions, as it may lead to deadlocks:
+ * drmBOUnmap(), drmFenceBuffers().
+ * The kernel is synchronizing and refcounting buffer maps. 
+ * User space only needs to refcount object usage within the same application.
+ */
+
+
 /*
  * List macros heavily inspired by the Linux kernel
  * list handling. No list looping yet.
@@ -82,6 +94,7 @@ typedef struct _drmMMListHead
     ((__type *)(((char *) (__item)) - offsetof(__type, __field)))
 
 
+
 typedef struct _drmBO{
     drm_bo_type_t type;
     unsigned handle;
-- 
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