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Subject[PATCH v2 4/5] ALSA: xen-front: Implement handling of shared buffers
Date
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.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@epam.com>
---
sound/xen/Makefile | 3 +-
sound/xen/xen_snd_front.c | 8 ++
sound/xen/xen_snd_front_shbuf.c | 193 ++++++++++++++++++++++++++++++++++++++++
sound/xen/xen_snd_front_shbuf.h | 36 ++++++++
4 files changed, 239 insertions(+), 1 deletion(-)
create mode 100644 sound/xen/xen_snd_front_shbuf.c
create mode 100644 sound/xen/xen_snd_front_shbuf.h

diff --git a/sound/xen/Makefile b/sound/xen/Makefile
index 03c669984000..f028bc30af5d 100644
--- a/sound/xen/Makefile
+++ b/sound/xen/Makefile
@@ -2,6 +2,7 @@

snd_xen_front-objs := xen_snd_front.o \
xen_snd_front_cfg.o \
- xen_snd_front_evtchnl.o
+ xen_snd_front_evtchnl.o \
+ xen_snd_front_shbuf.o

obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o
diff --git a/sound/xen/xen_snd_front.c b/sound/xen/xen_snd_front.c
index eb46bf4070f9..0569c6c596a3 100644
--- a/sound/xen/xen_snd_front.c
+++ b/sound/xen/xen_snd_front.c
@@ -11,6 +11,7 @@
#include <linux/delay.h>
#include <linux/module.h>

+#include <xen/page.h>
#include <xen/platform_pci.h>
#include <xen/xen.h>
#include <xen/xenbus.h>
@@ -186,6 +187,13 @@ static struct xenbus_driver xen_driver = {

static int __init xen_drv_init(void)
{
+ /* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
+ if (XEN_PAGE_SIZE != PAGE_SIZE) {
+ pr_err(XENSND_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
+ XEN_PAGE_SIZE, PAGE_SIZE);
+ return -ENODEV;
+ }
+
if (!xen_domain())
return -ENODEV;

diff --git a/sound/xen/xen_snd_front_shbuf.c b/sound/xen/xen_snd_front_shbuf.c
new file mode 100644
index 000000000000..6845dbc7fdf5
--- /dev/null
+++ b/sound/xen/xen_snd_front_shbuf.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+
+#include "xen_snd_front_shbuf.h"
+
+grant_ref_t xen_snd_front_shbuf_get_dir_start(struct xen_snd_front_shbuf *buf)
+{
+ if (!buf->grefs)
+ return GRANT_INVALID_REF;
+
+ return buf->grefs[0];
+}
+
+void xen_snd_front_shbuf_clear(struct xen_snd_front_shbuf *buf)
+{
+ memset(buf, 0, sizeof(*buf));
+}
+
+void xen_snd_front_shbuf_free(struct xen_snd_front_shbuf *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->directory);
+ free_pages_exact(buf->buffer, buf->buffer_sz);
+ xen_snd_front_shbuf_clear(buf);
+}
+
+/*
+ * number of grant references a page can hold with respect to the
+ * xensnd_page_directory header
+ */
+#define XENSND_NUM_GREFS_PER_PAGE ((XEN_PAGE_SIZE - \
+ offsetof(struct xensnd_page_directory, gref)) / \
+ sizeof(grant_ref_t))
+
+static void fill_page_dir(struct xen_snd_front_shbuf *buf,
+ int num_pages_dir)
+{
+ struct xensnd_page_directory *page_dir;
+ unsigned char *ptr;
+ int i, cur_gref, grefs_left, to_copy;
+
+ ptr = buf->directory;
+ 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 grant_references(struct xenbus_device *xb_dev,
+ struct xen_snd_front_shbuf *buf,
+ int num_pages_dir, int num_pages_buffer,
+ int num_grefs)
+{
+ grant_ref_t priv_gref_head;
+ unsigned long frame;
+ 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;
+ }
+
+ frame = xen_page_to_gfn(virt_to_page(buf->directory +
+ XEN_PAGE_SIZE * i));
+ gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
+ buf->grefs[j++] = cur_ref;
+ }
+
+ for (i = 0; i < num_pages_buffer; i++) {
+ cur_ref = gnttab_claim_grant_reference(&priv_gref_head);
+ if (cur_ref < 0) {
+ ret = cur_ref;
+ goto fail;
+ }
+
+ frame = xen_page_to_gfn(virt_to_page(buf->buffer +
+ XEN_PAGE_SIZE * i));
+ gnttab_grant_foreign_access_ref(cur_ref, otherend_id, frame, 0);
+ buf->grefs[j++] = cur_ref;
+ }
+
+ gnttab_free_grant_references(priv_gref_head);
+ fill_page_dir(buf, num_pages_dir);
+ return 0;
+
+fail:
+ gnttab_free_grant_references(priv_gref_head);
+ return ret;
+}
+
+static int alloc_int_buffers(struct xen_snd_front_shbuf *buf,
+ int num_pages_dir, int num_pages_buffer,
+ int num_grefs)
+{
+ buf->grefs = kcalloc(num_grefs, sizeof(*buf->grefs), GFP_KERNEL);
+ if (!buf->grefs)
+ return -ENOMEM;
+
+ buf->directory = kcalloc(num_pages_dir, XEN_PAGE_SIZE, GFP_KERNEL);
+ if (!buf->directory)
+ goto fail;
+
+ buf->buffer_sz = num_pages_buffer * XEN_PAGE_SIZE;
+ buf->buffer = alloc_pages_exact(buf->buffer_sz, GFP_KERNEL);
+ if (!buf->buffer)
+ goto fail;
+
+ return 0;
+
+fail:
+ kfree(buf->grefs);
+ buf->grefs = NULL;
+ kfree(buf->directory);
+ buf->directory = NULL;
+ return -ENOMEM;
+}
+
+int xen_snd_front_shbuf_alloc(struct xenbus_device *xb_dev,
+ struct xen_snd_front_shbuf *buf,
+ unsigned int buffer_sz)
+{
+ int num_pages_buffer, num_pages_dir, num_grefs;
+ int ret;
+
+ xen_snd_front_shbuf_clear(buf);
+
+ num_pages_buffer = DIV_ROUND_UP(buffer_sz, XEN_PAGE_SIZE);
+ /* number of pages the page directory consumes itself */
+ num_pages_dir = DIV_ROUND_UP(num_pages_buffer,
+ XENSND_NUM_GREFS_PER_PAGE);
+ num_grefs = num_pages_buffer + num_pages_dir;
+
+ ret = alloc_int_buffers(buf, num_pages_dir,
+ num_pages_buffer, num_grefs);
+ if (ret < 0)
+ return ret;
+
+ ret = grant_references(xb_dev, buf, num_pages_dir, num_pages_buffer,
+ num_grefs);
+ if (ret < 0)
+ return ret;
+
+ fill_page_dir(buf, num_pages_dir);
+ return 0;
+}
diff --git a/sound/xen/xen_snd_front_shbuf.h b/sound/xen/xen_snd_front_shbuf.h
new file mode 100644
index 000000000000..d28e97c47b2c
--- /dev/null
+++ b/sound/xen/xen_snd_front_shbuf.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_SND_FRONT_SHBUF_H
+#define __XEN_SND_FRONT_SHBUF_H
+
+#include <xen/grant_table.h>
+
+#include "xen_snd_front_evtchnl.h"
+
+struct xen_snd_front_shbuf {
+ int num_grefs;
+ grant_ref_t *grefs;
+ u8 *directory;
+ u8 *buffer;
+ size_t buffer_sz;
+};
+
+grant_ref_t xen_snd_front_shbuf_get_dir_start(struct xen_snd_front_shbuf *buf);
+
+int xen_snd_front_shbuf_alloc(struct xenbus_device *xb_dev,
+ struct xen_snd_front_shbuf *buf,
+ unsigned int buffer_sz);
+
+void xen_snd_front_shbuf_clear(struct xen_snd_front_shbuf *buf);
+
+void xen_snd_front_shbuf_free(struct xen_snd_front_shbuf *buf);
+
+#endif /* __XEN_SND_FRONT_SHBUF_H */
--
2.16.2
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