Date:   Mon,  7 Aug 2017 10:43:10 +0300
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     alsa-devel@...a-project.org, xen-devel@...ts.xen.org,
        linux-kernel@...r.kernel.org
Cc:     perex@...ex.cz, tiwai@...e.com, andr2000@...il.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: [PATCH 05/11] ALSA: vsnd: Implement handling of shared buffers

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>

Implement shared buffer handling according to the
para-virtualized sound device protocol at xen/interface/io/sndif.h:
- manage buffer memory
- handle granted references
- handle page directories

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
---
 sound/drivers/xen-front.c | 178 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 178 insertions(+)

diff --git a/sound/drivers/xen-front.c b/sound/drivers/xen-front.c
index a92459b2737e..04ebc15757f4 100644
--- a/sound/drivers/xen-front.c
+++ b/sound/drivers/xen-front.c
@@ -58,6 +58,14 @@ struct xdrv_evtchnl_info {
 	uint16_t resp_id;
 };
 
+struct sh_buf_info {
+	int num_grefs;
+	grant_ref_t *grefs;
+	uint8_t *vdirectory;
+	uint8_t *vbuffer;
+	size_t vbuffer_sz;
+};
+
 struct cfg_stream {
 	int unique_id;
 	char *xenstore_path;
@@ -825,6 +833,176 @@ static void xdrv_remove_internal(struct xdrv_info *drv_info)
 	xdrv_evtchnl_free_all(drv_info);
 }
 
+static inline grant_ref_t sh_buf_get_dir_start(struct sh_buf_info *buf)
+{
+	if (!buf->grefs)
+		return GRANT_INVALID_REF;
+	return buf->grefs[0];
+}
+
+static inline void sh_buf_clear(struct sh_buf_info *buf)
+{
+	memset(buf, 0, sizeof(*buf));
+}
+
+static void sh_buf_free(struct sh_buf_info *buf)
+{
+	int i;
+
+	if (buf->grefs) {
+		for (i = 0; i < buf->num_grefs; i++)
+			if (buf->grefs[i] != GRANT_INVALID_REF)
+				gnttab_end_foreign_access(buf->grefs[i],
+						0, 0UL);
+		kfree(buf->grefs);
+	}
+	kfree(buf->vdirectory);
+	free_pages_exact(buf->vbuffer, buf->vbuffer_sz);
+	sh_buf_clear(buf);
+}
+
+/*
+ * number of grant references a page can hold with respect to the
+ * xendispl_page_directory header
+ */
+#define XENSND_NUM_GREFS_PER_PAGE ((XEN_PAGE_SIZE - \
+	offsetof(struct xensnd_page_directory, gref)) / \
+	sizeof(grant_ref_t))
+
+static void sh_buf_fill_page_dir(struct sh_buf_info *buf, int num_pages_dir)
+{
+	struct xensnd_page_directory *page_dir;
+	unsigned char *ptr;
+	int i, cur_gref, grefs_left, to_copy;
+
+	ptr = buf->vdirectory;
+	grefs_left = buf->num_grefs - num_pages_dir;
+	/*
+	 * skip grant references at the beginning, they are for pages granted
+	 * for the page directory itself
+	 */
+	cur_gref = num_pages_dir;
+	for (i = 0; i < num_pages_dir; i++) {
+		page_dir = (struct xensnd_page_directory *)ptr;
+		if (grefs_left <= XENSND_NUM_GREFS_PER_PAGE) {
+			to_copy = grefs_left;
+			page_dir->gref_dir_next_page = GRANT_INVALID_REF;
+		} else {
+			to_copy = XENSND_NUM_GREFS_PER_PAGE;
+			page_dir->gref_dir_next_page = buf->grefs[i + 1];
+		}
+		memcpy(&page_dir->gref, &buf->grefs[cur_gref],
+			to_copy * sizeof(grant_ref_t));
+		ptr += XEN_PAGE_SIZE;
+		grefs_left -= to_copy;
+		cur_gref += to_copy;
+	}
+}
+
+static int sh_buf_grant_refs(struct xenbus_device *xb_dev,
+	struct sh_buf_info *buf,
+	int num_pages_dir, int num_pages_vbuffer, int num_grefs)
+{
+	grant_ref_t priv_gref_head;
+	int ret, i, j, cur_ref;
+	int otherend_id;
+
+	ret = gnttab_alloc_grant_references(num_grefs, &priv_gref_head);
+	if (ret)
+		return ret;
+
+	buf->num_grefs = num_grefs;
+	otherend_id = xb_dev->otherend_id;
+	j = 0;
+
+	for (i = 0; i < num_pages_dir; i++) {
+		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
+		if (cur_ref < 0) {
+			ret = cur_ref;
+			goto fail;
+		}
+
+		gnttab_grant_foreign_access_ref(cur_ref, otherend_id,
+			xen_page_to_gfn(virt_to_page(buf->vdirectory +
+				XEN_PAGE_SIZE * i)), 0);
+		buf->grefs[j++] = cur_ref;
+	}
+
+	for (i = 0; i < num_pages_vbuffer; i++) {
+		cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
+		if (cur_ref < 0) {
+			ret = cur_ref;
+			goto fail;
+		}
+
+		gnttab_grant_foreign_access_ref(cur_ref, otherend_id,
+			xen_page_to_gfn(virt_to_page(buf->vbuffer +
+				XEN_PAGE_SIZE * i)), 0);
+		buf->grefs[j++] = cur_ref;
+	}
+
+	gnttab_free_grant_references(priv_gref_head);
+	sh_buf_fill_page_dir(buf, num_pages_dir);
+	return 0;
+
+fail:
+	gnttab_free_grant_references(priv_gref_head);
+	return ret;
+}
+
+static int sh_buf_alloc_int_buffers(struct sh_buf_info *buf,
+		int num_pages_dir, int num_pages_vbuffer, int num_grefs)
+{
+	buf->grefs = kcalloc(num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
+	if (!buf->grefs)
+		return -ENOMEM;
+
+	buf->vdirectory = kcalloc(num_pages_dir, XEN_PAGE_SIZE, GFP_KERNEL);
+	if (!buf->vdirectory)
+		goto fail;
+
+	buf->vbuffer_sz = num_pages_vbuffer * XEN_PAGE_SIZE;
+	buf->vbuffer = alloc_pages_exact(buf->vbuffer_sz, GFP_KERNEL);
+	if (!buf->vbuffer)
+		goto fail;
+	return 0;
+
+fail:
+	kfree(buf->grefs);
+	buf->grefs = NULL;
+	kfree(buf->vdirectory);
+	buf->vdirectory = NULL;
+	return -ENOMEM;
+}
+
+static int sh_buf_alloc(struct xenbus_device *xb_dev,
+	struct sh_buf_info *buf, unsigned int buffer_size)
+{
+	int num_pages_vbuffer, num_pages_dir, num_grefs;
+	int ret;
+
+	sh_buf_clear(buf);
+
+	num_pages_vbuffer = DIV_ROUND_UP(buffer_size, XEN_PAGE_SIZE);
+	/* number of pages the page directory consumes itself */
+	num_pages_dir = DIV_ROUND_UP(num_pages_vbuffer,
+		XENSND_NUM_GREFS_PER_PAGE);
+	num_grefs = num_pages_vbuffer + num_pages_dir;
+
+	ret = sh_buf_alloc_int_buffers(buf, num_pages_dir,
+		num_pages_vbuffer, num_grefs);
+	if (ret < 0)
+		return ret;
+
+	ret = sh_buf_grant_refs(xb_dev, buf,
+		num_pages_dir, num_pages_vbuffer, num_grefs);
+	if (ret < 0)
+		return ret;
+
+	sh_buf_fill_page_dir(buf, num_pages_dir);
+	return 0;
+}
+
 static int xdrv_be_on_initwait(struct xdrv_info *drv_info)
 {
 	int stream_idx;
-- 
2.7.4

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