drm: Add generic multipart buffer.

Allocating multiple pages of memory for data that is coming
from user space may fail. To fix memory allocation failures
the buffer object should be split to multiple independ pages.

drm buffer provides generic interface to copy and process
large data arrays from user space.

Interface includes allocation and free functions to allocate
the buffer object and data storage pages.

All access operations are performed relative to a internal
pointer which is advanced with drm_buffer_advance function.

The buffer can be accessed using drm_buffer_pointer_to_XXX
functions if it is known that requested object doesn't split
over a page boundary. These functions don't do any error
checking to maximize performance.

If there is large object which could be split there is special
drm_buffer_read_object function. drm_buffer_read_object takes
a pointer as argument which is used as temporary store for
data if it is split over boundary in the buffer.

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

2 files changed, 185 insertions, 1 deletions

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 39c5aa75b8f1..abe3f446ca48 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -4,7 +4,7 @@
 
 ccflags-y := -Iinclude/drm
 
-drm-y       :=  drm_auth.o drm_bufs.o drm_cache.o \
+drm-y       :=  drm_auth.o drm_buffer.o drm_bufs.o drm_cache.o \
                 drm_context.o drm_dma.o drm_drawable.o \
                 drm_drv.o drm_fops.o drm_gem.o drm_ioctl.o drm_irq.o \
                 drm_lock.o drm_memory.o drm_proc.o drm_stub.o drm_vm.o \
diff --git a/drivers/gpu/drm/drm_buffer.c b/drivers/gpu/drm/drm_buffer.c
new file mode 100644
index 000000000000..55d03ed05000
--- /dev/null
+++ b/drivers/gpu/drm/drm_buffer.c
@@ -0,0 +1,184 @@
+/**************************************************************************
+ *
+ * Copyright 2010 Pauli Nieminen.
+ * All Rights Reserved.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sub license, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial portions
+ * of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+ * USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ *
+ **************************************************************************/
+/*
+ * Multipart buffer for coping data which is larger than the page size.
+ *
+ * Authors:
+ * Pauli Nieminen <suokkos-at-gmail-dot-com>
+ */
+
+#include "drm_buffer.h"
+
+/**
+ * Allocate the drm buffer object.
+ *
+ *   buf: Pointer to a pointer where the object is stored.
+ *   size: The number of bytes to allocate.
+ */
+int drm_buffer_alloc(struct drm_buffer **buf, int size)
+{
+        int nr_pages = size / PAGE_SIZE + 1;
+        int idx;
+
+        /* Allocating pointer table to end of structure makes drm_buffer
+         * variable sized */
+        *buf = kzalloc(sizeof(struct drm_buffer) + nr_pages*sizeof(char *),
+                        GFP_KERNEL);
+
+        if (*buf == NULL) {
+                DRM_ERROR("Failed to allocate drm buffer object to hold"
+                                " %d bytes in %d pages.\n",
+                                size, nr_pages);
+                return -ENOMEM;
+        }
+
+        (*buf)->size = size;
+
+        for (idx = 0; idx < nr_pages; ++idx) {
+
+                (*buf)->data[idx] =
+                        kmalloc(min(PAGE_SIZE, size - idx * PAGE_SIZE),
+                                GFP_KERNEL);
+
+
+                if ((*buf)->data[idx] == NULL) {
+                        DRM_ERROR("Failed to allocate %dth page for drm"
+                                        " buffer with %d bytes and %d pages.\n",
+                                        idx + 1, size, nr_pages);
+                        goto error_out;
+                }
+
+        }
+
+        return 0;
+
+error_out:
+
+        /* Only last element can be null pointer so check for it first. */
+        if ((*buf)->data[idx])
+                kfree((*buf)->data[idx]);
+
+        for (--idx; idx >= 0; --idx)
+                kfree((*buf)->data[idx]);
+
+        kfree(*buf);
+        return -ENOMEM;
+}
+EXPORT_SYMBOL(drm_buffer_alloc);
+
+/**
+ * Copy the user data to the begin of the buffer and reset the processing
+ * iterator.
+ *
+ *   user_data: A pointer the data that is copied to the buffer.
+ *   size: The Number of bytes to copy.
+ */
+extern int drm_buffer_copy_from_user(struct drm_buffer *buf,
+                void __user *user_data, int size)
+{
+        int nr_pages = size / PAGE_SIZE + 1;
+        int idx;
+
+        if (size > buf->size) {
+                DRM_ERROR("Requesting to copy %d bytes to a drm buffer with"
+                                " %d bytes space\n",
+                                size, buf->size);
+                return -EFAULT;
+        }
+
+        for (idx = 0; idx < nr_pages; ++idx) {
+
+                if (DRM_COPY_FROM_USER(buf->data[idx],
+                        user_data + idx * PAGE_SIZE,
+                        min(PAGE_SIZE, size - idx * PAGE_SIZE))) {
+                        DRM_ERROR("Failed to copy user data (%p) to drm buffer"
+                                        " (%p) %dth page.\n",
+                                        user_data, buf, idx);
+                        return -EFAULT;
+
+                }
+        }
+        buf->iterator = 0;
+        return 0;
+}
+EXPORT_SYMBOL(drm_buffer_copy_from_user);
+
+/**
+ * Free the drm buffer object
+ */
+void drm_buffer_free(struct drm_buffer *buf)
+{
+
+        if (buf != NULL) {
+
+                int nr_pages = buf->size / PAGE_SIZE + 1;
+                int idx;
+                for (idx = 0; idx < nr_pages; ++idx)
+                        kfree(buf->data[idx]);
+
+                kfree(buf);
+        }
+}
+EXPORT_SYMBOL(drm_buffer_free);
+
+/**
+ * Read an object from buffer that may be split to multiple parts. If object
+ * is not split function just returns the pointer to object in buffer. But in
+ * case of split object data is copied to given stack object that is suplied
+ * by caller.
+ *
+ * The processing location of the buffer is also advanced to the next byte
+ * after the object.
+ *
+ *   objsize: The size of the objet in bytes.
+ *   stack_obj: A pointer to a memory location where object can be copied.
+ */
+void *drm_buffer_read_object(struct drm_buffer *buf,
+                int objsize, void *stack_obj)
+{
+        int idx = drm_buffer_index(buf);
+        int page = drm_buffer_page(buf);
+        void *obj = 0;
+
+        if (idx + objsize <= PAGE_SIZE) {
+                obj = &buf->data[page][idx];
+        } else {
+                /* The object is split which forces copy to temporary object.*/
+                int beginsz = PAGE_SIZE - idx;
+                memcpy(stack_obj, &buf->data[page][idx], beginsz);
+
+                memcpy(stack_obj + beginsz, &buf->data[page + 1][0],
+                                objsize - beginsz);
+
+                obj = stack_obj;
+        }
+
+        drm_buffer_advance(buf, objsize);
+        return obj;
+}
+EXPORT_SYMBOL(drm_buffer_read_object);