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Subject[PATCH v3 5/9] xen/gntdev: Allow mappings for DMA buffers
Date
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

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@epam.com>
---
drivers/xen/gntdev.c | 99 ++++++++++++++++++++++++++++++++++++++-
include/uapi/xen/gntdev.h | 15 ++++++
2 files changed, 112 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index bd56653b9bbc..d6b79ad1cd6f 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 +104,27 @@ 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.
+ */
+
+ struct device *dma_dev;
+ /* Flags used to create this DMA buffer: GNTDEV_DMA_FLAG_XXX. */
+ int dma_flags;
+ void *dma_vaddr;
+ dma_addr_t dma_bus_addr;
+ /* Needed to avoid allocation in gnttab_dma_free_pages(). */
+ xen_pfn_t *frames;
+#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 +146,27 @@ 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.frames = map->frames;
+ args.vaddr = map->dma_vaddr;
+ args.dev_bus_addr = map->dma_bus_addr;
+
+ gnttab_dma_free_pages(&args);
+ } else
+#endif
if (map->pages)
gnttab_free_pages(map->count, map->pages);
+
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+ kfree(map->frames);
+#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;
@@ -155,6 +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;
+
+ add->frames = kcalloc(count, sizeof(add->frames[0]),
+ GFP_KERNEL);
+ if (!add->frames)
+ goto err;
+
+ /* 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;
+ args.frames = add->frames;
+
+ if (gnttab_dma_alloc_pages(&args))
+ goto err;
+
+ add->dma_vaddr = args.vaddr;
+ add->dma_bus_addr = args.dev_bus_addr;
+ } else
+#endif
if (gnttab_alloc_pages(count, add->pages))
goto err;

@@ -325,6 +401,14 @@ static int map_grant_pages(struct grant_map *map)
map->unmap_ops[i].handle = map->map_ops[i].handle;
if (use_ptemod)
map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
+#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
+ else if (map->dma_vaddr) {
+ unsigned long mfn;
+
+ mfn = pfn_to_bfn(page_to_pfn(map->pages[i]));
+ map->unmap_ops[i].dev_bus_addr = __pfn_to_phys(mfn);
+ }
+#endif
}
return err;
}
@@ -548,6 +632,17 @@ 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 +684,7 @@ 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..4b9d498a31d4 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 << 0)
+
+/*
+ * The buffer is backed with memory allocated with dma_alloc_coherent.
+ */
+#define GNTDEV_DMA_FLAG_COHERENT (1 << 1)
+
#endif /* __LINUX_PUBLIC_GNTDEV_H__ */
--
2.17.1
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