[media] v4l: vb2-dma-contig: add support for scatterlist in userptr mode

This patch introduces usage of dma_map_sg to map memory behind
a userspace pointer to a device as dma-contiguous mapping.
This patch contains some of the code kindly provided by Marek Szyprowski
<m.szyprowski@samsung.com> and Kamil Debski <k.debski@samsung.com> and Andrzej
Pietrasiewicz <andrzej.p@samsung.com>. Kind thanks for bug reports from Laurent
Pinchart <laurent.pinchart@ideasonboard.com> and Seung-Woo Kim
<sw0312.kim@samsung.com>.

Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 210 insertions, 16 deletions

diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
index daac2b2de357..8486e06cb618 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
@@ -11,6 +11,8 @@
  */
 
 #include <linux/module.h>
+#include <linux/scatterlist.h>
+#include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/dma-mapping.h>
 
@@ -27,6 +29,8 @@ struct vb2_dc_buf {
         void                            *vaddr;
         unsigned long                   size;
         dma_addr_t                      dma_addr;
+        enum dma_data_direction         dma_dir;
+        struct sg_table                 *dma_sgt;
 
         /* MMAP related */
         struct vb2_vmarea_handler       handler;
@@ -37,6 +41,44 @@ struct vb2_dc_buf {
 };
 
 /*********************************************/
+/*        scatterlist table functions        */
+/*********************************************/
+
+
+static void vb2_dc_sgt_foreach_page(struct sg_table *sgt,
+        void (*cb)(struct page *pg))
+{
+        struct scatterlist *s;
+        unsigned int i;
+
+        for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
+                struct page *page = sg_page(s);
+                unsigned int n_pages = PAGE_ALIGN(s->offset + s->length)
+                        >> PAGE_SHIFT;
+                unsigned int j;
+
+                for (j = 0; j < n_pages; ++j, ++page)
+                        cb(page);
+        }
+}
+
+static unsigned long vb2_dc_get_contiguous_size(struct sg_table *sgt)
+{
+        struct scatterlist *s;
+        dma_addr_t expected = sg_dma_address(sgt->sgl);
+        unsigned int i;
+        unsigned long size = 0;
+
+        for_each_sg(sgt->sgl, s, sgt->nents, i) {
+                if (sg_dma_address(s) != expected)
+                        break;
+                expected = sg_dma_address(s) + sg_dma_len(s);
+                size += sg_dma_len(s);
+        }
+        return size;
+}
+
+/*********************************************/
 /*         callbacks for all buffers         */
 /*********************************************/
 
@@ -122,42 +164,194 @@ static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma)
 /*       callbacks for USERPTR buffers       */
 /*********************************************/
 
+static inline int vma_is_io(struct vm_area_struct *vma)
+{
+        return !!(vma->vm_flags & (VM_IO | VM_PFNMAP));
+}
+
+static int vb2_dc_get_user_pages(unsigned long start, struct page **pages,
+        int n_pages, struct vm_area_struct *vma, int write)
+{
+        if (vma_is_io(vma)) {
+                unsigned int i;
+
+                for (i = 0; i < n_pages; ++i, start += PAGE_SIZE) {
+                        unsigned long pfn;
+                        int ret = follow_pfn(vma, start, &pfn);
+
+                        if (ret) {
+                                pr_err("no page for address %lu\n", start);
+                                return ret;
+                        }
+                        pages[i] = pfn_to_page(pfn);
+                }
+        } else {
+                int n;
+
+                n = get_user_pages(current, current->mm, start & PAGE_MASK,
+                        n_pages, write, 1, pages, NULL);
+                /* negative error means that no page was pinned */
+                n = max(n, 0);
+                if (n != n_pages) {
+                        pr_err("got only %d of %d user pages\n", n, n_pages);
+                        while (n)
+                                put_page(pages[--n]);
+                        return -EFAULT;
+                }
+        }
+
+        return 0;
+}
+
+static void vb2_dc_put_dirty_page(struct page *page)
+{
+        set_page_dirty_lock(page);
+        put_page(page);
+}
+
+static void vb2_dc_put_userptr(void *buf_priv)
+{
+        struct vb2_dc_buf *buf = buf_priv;
+        struct sg_table *sgt = buf->dma_sgt;
+
+        dma_unmap_sg(buf->dev, sgt->sgl, sgt->orig_nents, buf->dma_dir);
+        if (!vma_is_io(buf->vma))
+                vb2_dc_sgt_foreach_page(sgt, vb2_dc_put_dirty_page);
+
+        sg_free_table(sgt);
+        kfree(sgt);
+        vb2_put_vma(buf->vma);
+        kfree(buf);
+}
+
 static void *vb2_dc_get_userptr(void *alloc_ctx, unsigned long vaddr,
-                                        unsigned long size, int write)
+        unsigned long size, int write)
 {
+        struct vb2_dc_conf *conf = alloc_ctx;
         struct vb2_dc_buf *buf;
+        unsigned long start;
+        unsigned long end;
+        unsigned long offset;
+        struct page **pages;
+        int n_pages;
+        int ret = 0;
         struct vm_area_struct *vma;
-        dma_addr_t dma_addr = 0;
-        int ret;
+        struct sg_table *sgt;
+        unsigned long contig_size;
 
         buf = kzalloc(sizeof *buf, GFP_KERNEL);
         if (!buf)
                 return ERR_PTR(-ENOMEM);
 
-        ret = vb2_get_contig_userptr(vaddr, size, &vma, &dma_addr);
+        buf->dev = conf->dev;
+        buf->dma_dir = write ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+
+        start = vaddr & PAGE_MASK;
+        offset = vaddr & ~PAGE_MASK;
+        end = PAGE_ALIGN(vaddr + size);
+        n_pages = (end - start) >> PAGE_SHIFT;
+
+        pages = kmalloc(n_pages * sizeof(pages[0]), GFP_KERNEL);
+        if (!pages) {
+                ret = -ENOMEM;
+                pr_err("failed to allocate pages table\n");
+                goto fail_buf;
+        }
+
+        /* current->mm->mmap_sem is taken by videobuf2 core */
+        vma = find_vma(current->mm, vaddr);
+        if (!vma) {
+                pr_err("no vma for address %lu\n", vaddr);
+                ret = -EFAULT;
+                goto fail_pages;
+        }
+
+        if (vma->vm_end < vaddr + size) {
+                pr_err("vma at %lu is too small for %lu bytes\n", vaddr, size);
+                ret = -EFAULT;
+                goto fail_pages;
+        }
+
+        buf->vma = vb2_get_vma(vma);
+        if (!buf->vma) {
+                pr_err("failed to copy vma\n");
+                ret = -ENOMEM;
+                goto fail_pages;
+        }
+
+        /* extract page list from userspace mapping */
+        ret = vb2_dc_get_user_pages(start, pages, n_pages, vma, write);
         if (ret) {
-                printk(KERN_ERR "Failed acquiring VMA for vaddr 0x%08lx\n",
-                                vaddr);
-                kfree(buf);
-                return ERR_PTR(ret);
+                pr_err("failed to get user pages\n");
+                goto fail_vma;
+        }
+
+        sgt = kzalloc(sizeof(*sgt), GFP_KERNEL);
+        if (!sgt) {
+                pr_err("failed to allocate sg table\n");
+                ret = -ENOMEM;
+                goto fail_get_user_pages;
+        }
+
+        ret = sg_alloc_table_from_pages(sgt, pages, n_pages,
+                offset, size, GFP_KERNEL);
+        if (ret) {
+                pr_err("failed to initialize sg table\n");
+                goto fail_sgt;
+        }
+
+        /* pages are no longer needed */
+        kfree(pages);
+        pages = NULL;
+
+        sgt->nents = dma_map_sg(buf->dev, sgt->sgl, sgt->orig_nents,
+                buf->dma_dir);
+        if (sgt->nents <= 0) {
+                pr_err("failed to map scatterlist\n");
+                ret = -EIO;
+                goto fail_sgt_init;
+        }
+
+        contig_size = vb2_dc_get_contiguous_size(sgt);
+        if (contig_size < size) {
+                pr_err("contiguous mapping is too small %lu/%lu\n",
+                        contig_size, size);
+                ret = -EFAULT;
+                goto fail_map_sg;
         }
 
+        buf->dma_addr = sg_dma_address(sgt->sgl);
         buf->size = size;
-        buf->dma_addr = dma_addr;
-        buf->vma = vma;
+        buf->dma_sgt = sgt;
 
         return buf;
-}
 
-static void vb2_dc_put_userptr(void *mem_priv)
-{
-        struct vb2_dc_buf *buf = mem_priv;
+fail_map_sg:
+        dma_unmap_sg(buf->dev, sgt->sgl, sgt->orig_nents, buf->dma_dir);
 
-        if (!buf)
-                return;
+fail_sgt_init:
+        if (!vma_is_io(buf->vma))
+                vb2_dc_sgt_foreach_page(sgt, put_page);
+        sg_free_table(sgt);
+
+fail_sgt:
+        kfree(sgt);
 
+fail_get_user_pages:
+        if (pages && !vma_is_io(buf->vma))
+                while (n_pages)
+                        put_page(pages[--n_pages]);
+
+fail_vma:
         vb2_put_vma(buf->vma);
+
+fail_pages:
+        kfree(pages); /* kfree is NULL-proof */
+
+fail_buf:
         kfree(buf);
+
+        return ERR_PTR(ret);
 }
 
 /*********************************************/