[Xen-devel] [PATCH 4/8] xen/gntdev: Allow mappings for DMA buffers

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

Allow mappings for DMA backed  buffers if grant table module
supports such: this extends grant device to not only map buffers
made of balloon pages, but also from buffers allocated with
dma_alloc_xxx.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
 drivers/xen/gntdev.c      | 100 +++++++++++++++++++++++++++++++++++++-
 include/uapi/xen/gntdev.h |  15 ++++++
 2 files changed, 113 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index bd56653b9bbc..640a579f42ea 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -37,6 +37,9 @@
 #include <linux/slab.h>
 #include <linux/highmem.h>
 #include <linux/refcount.h>
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+#include <linux/of_device.h>
+#endif
 
 #include <xen/xen.h>
 #include <xen/grant_table.h>
@@ -72,6 +75,11 @@ struct gntdev_priv {
        struct mutex lock;
        struct mm_struct *mm;
        struct mmu_notifier mn;
+
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+       /* Device for which DMA memory is allocated. */
+       struct device *dma_dev;
+#endif
 };
 
 struct unmap_notify {
@@ -96,10 +104,28 @@ struct grant_map {
        struct gnttab_unmap_grant_ref *kunmap_ops;
        struct page **pages;
        unsigned long pages_vm_start;
+
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+       /*
+        * If dmabuf_vaddr is not NULL then this mapping is backed by DMA
+        * capable memory.
+        */
+
+       /* Device for which DMA memory is allocated. */
+       struct device *dma_dev;
+       /* Flags used to create this DMA buffer: GNTDEV_DMABUF_FLAG_XXX. */
+       bool dma_flags;
+       /* Virtual/CPU address of the DMA buffer. */
+       void *dma_vaddr;
+       /* Bus address of the DMA buffer. */
+       dma_addr_t dma_bus_addr;
+#endif
 };
 
 static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
 
+static struct miscdevice gntdev_miscdev;
+
 /* ------------------------------------------------------------------ */
 
 static void gntdev_print_maps(struct gntdev_priv *priv,
@@ -121,8 +147,26 @@ static void gntdev_free_map(struct grant_map *map)
        if (map == NULL)
                return;
 
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+       if (map->dma_vaddr) {
+               struct gnttab_dma_alloc_args args;
+
+               args.dev = map->dma_dev;
+               args.coherent = map->dma_flags & GNTDEV_DMA_FLAG_COHERENT;
+               args.nr_pages = map->count;
+               args.pages = map->pages;
+               args.vaddr = map->dma_vaddr;
+               args.dev_bus_addr = map->dma_bus_addr;
+
+               gnttab_dma_free_pages(&args);
+       } else if (map->pages) {
+               gnttab_free_pages(map->count, map->pages);
+       }
+#else
        if (map->pages)
                gnttab_free_pages(map->count, map->pages);
+#endif
+
        kfree(map->pages);
        kfree(map->grants);
        kfree(map->map_ops);
@@ -132,7 +176,8 @@ static void gntdev_free_map(struct grant_map *map)
        kfree(map);
 }
 
-static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
+static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count,
+                                         int dma_flags)
 {
        struct grant_map *add;
        int i;
@@ -155,8 +200,37 @@ static struct grant_map *gntdev_alloc_map(struct 
gntdev_priv *priv, int count)
            NULL == add->pages)
                goto err;
 
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+       add->dma_flags = dma_flags;
+
+       /*
+        * Check if this mapping is requested to be backed
+        * by a DMA buffer.
+        */
+       if (dma_flags & (GNTDEV_DMA_FLAG_WC | GNTDEV_DMA_FLAG_COHERENT)) {
+               struct gnttab_dma_alloc_args args;
+
+               /* Remember the device, so we can free DMA memory. */
+               add->dma_dev = priv->dma_dev;
+
+               args.dev = priv->dma_dev;
+               args.coherent = dma_flags & GNTDEV_DMA_FLAG_COHERENT;
+               args.nr_pages = count;
+               args.pages = add->pages;
+
+               if (gnttab_dma_alloc_pages(&args))
+                       goto err;
+
+               add->dma_vaddr = args.vaddr;
+               add->dma_bus_addr = args.dev_bus_addr;
+       } else {
+               if (gnttab_alloc_pages(count, add->pages))
+                       goto err;
+       }
+#else
        if (gnttab_alloc_pages(count, add->pages))
                goto err;
+#endif
 
        for (i = 0; i < count; i++) {
                add->map_ops[i].handle = -1;
@@ -323,8 +397,19 @@ static int map_grant_pages(struct grant_map *map)
                }
 
                map->unmap_ops[i].handle = map->map_ops[i].handle;
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+               if (use_ptemod) {
+                       map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
+               } else if (map->dma_vaddr) {
+                       unsigned long mfn;
+
+                       mfn = __pfn_to_mfn(page_to_pfn(map->pages[i]));
+                       map->unmap_ops[i].dev_bus_addr = __pfn_to_phys(mfn);
+               }
+#else
                if (use_ptemod)
                        map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
+#endif
        }
        return err;
 }
@@ -548,6 +633,17 @@ static int gntdev_open(struct inode *inode, struct file 
*flip)
        }
 
        flip->private_data = priv;
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+       priv->dma_dev = gntdev_miscdev.this_device;
+
+       /*
+        * The device is not spawn from a device tree, so arch_setup_dma_ops
+        * is not called, thus leaving the device with dummy DMA ops.
+        * Fix this call of_dma_configure() with a NULL node to set
+        * default DMA ops.
+        */
+       of_dma_configure(priv->dma_dev, NULL);
+#endif
        pr_debug("priv %p\n", priv);
 
        return 0;
@@ -589,7 +685,7 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv 
*priv,
                return -EINVAL;
 
        err = -ENOMEM;
-       map = gntdev_alloc_map(priv, op.count);
+       map = gntdev_alloc_map(priv, op.count, 0 /* This is not a dma-buf. */);
        if (!map)
                return err;
 
diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h
index 6d1163456c03..2d5a4672f07c 100644
--- a/include/uapi/xen/gntdev.h
+++ b/include/uapi/xen/gntdev.h
@@ -200,4 +200,19 @@ struct ioctl_gntdev_grant_copy {
 /* Send an interrupt on the indicated event channel */
 #define UNMAP_NOTIFY_SEND_EVENT 0x2
 
+/*
+ * Flags to be used while requesting memory mapping's backing storage
+ * to be allocated with DMA API.
+ */
+
+/*
+ * The buffer is backed with memory allocated with dma_alloc_wc.
+ */
+#define GNTDEV_DMA_FLAG_WC             (1 << 1)
+
+/*
+ * The buffer is backed with memory allocated with dma_alloc_coherent.
+ */
+#define GNTDEV_DMA_FLAG_COHERENT       (1 << 2)
+
 #endif /* __LINUX_PUBLIC_GNTDEV_H__ */
-- 
2.17.0


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