[PATCH v2 2/4] usb: xhci: sideband: allocate sideband ring segments from a dedicated pool
From: Wesley Cheng
Date: Fri Aug 28 2026 - 17:40:30 EST
Ring segments are normally allocated from a shared DMA pool sized and
aligned to TRB_SEGMENT_SIZE (4096 bytes). On kernels built with a
larger PAGE_SIZE (e.g. 16K or 64K page arches), a segment can end up
at a non-page-aligned offset within its enclosing CPU page, and
multiple segments can share the same physical page.
A sideband client that maps a ring buffer directly via the IOMMU
(which operates at page granularity) needs to know exactly which
page(s) back the ring, and only pages that are actually intended to
be exposed to that client should ever be mapped this way.
Give each xhci_sideband instance its own segment_pool, allocated
separately from the core xhci->segment_pool, so every segment backing
a sideband-tagged endpoint always comes from a page that is meant to
be ADSP-visible. Normal (non-offloaded) endpoints are unaffected, as
they keep allocating from xhci->segment_pool.
Thread the pool to use through xhci_ring_alloc_from_pool(),
xhci_alloc_interrupter() and xhci_create_secondary_interrupter(), and
have xhci_endpoint_init() pick virt_dev->eps[ep_index].sideband's pool
over xhci->segment_pool when the endpoint has already been tagged by
xhci_sideband_add_endpoint(). Endpoint tagging always precedes ring
allocation, since UAC streaming endpoints aren't allocated a ring
until usb_set_interface() activates the streaming altsetting, well
after the sideband client has already tagged them.
Move EP_CTX_PER_DEV, TRBS_PER_SEGMENT and TRB_SEGMENT_SIZE into
xhci-sideband.h as the shared canonical definitions, replacing the
"FIXME defined twice" duplicate in xhci.h.
Have xhci_sideband_register() take the segment pool as an argument
instead of creating it internally, so the sideband client that
actually consumes the pool (qc_audio_offload.c) owns its full
lifetime: create it before xhci_sideband_register(), destroy it after
xhci_sideband_unregister() or a failed register call. The client picks
the DMA device the same way it already does elsewhere in that file
(interface_to_usbdev(intf)->bus->sysdev) without needing an
xhci-internal accessor for xhci->page_size.
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Wesley Cheng <wesley.cheng@xxxxxxxxxxxxxxxx>
---
drivers/usb/host/xhci-mem.c | 64 +++++++++++++++++++++++++--------------
drivers/usb/host/xhci-sideband.c | 14 +++++++--
drivers/usb/host/xhci.h | 14 ++++-----
include/linux/usb/xhci-sideband.h | 22 +++++++++++++-
sound/usb/qcom/qc_audio_offload.c | 21 +++++++++++--
5 files changed, 100 insertions(+), 35 deletions(-)
diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index 7a21ac81f9c8..bf7eb53abab9 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -15,6 +15,7 @@
#include <linux/dmapool.h>
#include <linux/dma-mapping.h>
#include <linux/bitfield.h>
+#include <linux/usb/xhci-sideband.h>
#include "xhci.h"
#include "xhci-trace.h"
@@ -28,6 +29,7 @@
* "All components of all Command and Transfer TRBs shall be initialized to '0'"
*/
static struct xhci_segment *xhci_segment_alloc(struct xhci_hcd *xhci,
+ struct dma_pool *pool,
unsigned int max_packet,
unsigned int num,
gfp_t flags)
@@ -40,7 +42,7 @@ static struct xhci_segment *xhci_segment_alloc(struct xhci_hcd *xhci,
if (!seg)
return NULL;
- seg->trbs = dma_pool_zalloc(xhci->segment_pool, flags, &dma);
+ seg->trbs = dma_pool_zalloc(pool, flags, &dma);
if (!seg->trbs) {
kfree(seg);
return NULL;
@@ -50,7 +52,7 @@ static struct xhci_segment *xhci_segment_alloc(struct xhci_hcd *xhci,
seg->bounce_buf = kzalloc_node(max_packet, flags,
dev_to_node(dev));
if (!seg->bounce_buf) {
- dma_pool_free(xhci->segment_pool, seg->trbs, dma);
+ dma_pool_free(pool, seg->trbs, dma);
kfree(seg);
return NULL;
}
@@ -62,10 +64,11 @@ static struct xhci_segment *xhci_segment_alloc(struct xhci_hcd *xhci,
return seg;
}
-static void xhci_segment_free(struct xhci_hcd *xhci, struct xhci_segment *seg)
+static void xhci_segment_free(struct xhci_hcd *xhci, struct dma_pool *pool,
+ struct xhci_segment *seg)
{
if (seg->trbs) {
- dma_pool_free(xhci->segment_pool, seg->trbs, seg->dma);
+ dma_pool_free(pool, seg->trbs, seg->dma);
seg->trbs = NULL;
}
kfree(seg->bounce_buf);
@@ -81,7 +84,7 @@ static void xhci_ring_segments_free(struct xhci_hcd *xhci, struct xhci_ring *rin
while (seg) {
next = seg->next;
- xhci_segment_free(xhci, seg);
+ xhci_segment_free(xhci, ring->segment_pool, seg);
seg = next;
}
}
@@ -334,7 +337,7 @@ static int xhci_alloc_segments_for_ring(struct xhci_hcd *xhci, struct xhci_ring
struct xhci_segment *prev;
unsigned int num = 0;
- prev = xhci_segment_alloc(xhci, ring->bounce_buf_len, num, flags);
+ prev = xhci_segment_alloc(xhci, ring->segment_pool, ring->bounce_buf_len, num, flags);
if (!prev)
return -ENOMEM;
num++;
@@ -343,7 +346,8 @@ static int xhci_alloc_segments_for_ring(struct xhci_hcd *xhci, struct xhci_ring
while (num < ring->num_segs) {
struct xhci_segment *next;
- next = xhci_segment_alloc(xhci, ring->bounce_buf_len, num, flags);
+ next = xhci_segment_alloc(xhci, ring->segment_pool, ring->bounce_buf_len,
+ num, flags);
if (!next)
goto free_segments;
@@ -362,15 +366,10 @@ static int xhci_alloc_segments_for_ring(struct xhci_hcd *xhci, struct xhci_ring
return -ENOMEM;
}
-/*
- * Create a new ring with zero or more segments.
- *
- * Link each segment together into a ring.
- * Set the end flag and the cycle toggle bit on the last segment.
- * See section 4.9.1 and figures 15 and 16.
- */
-struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci, unsigned int num_segs,
- enum xhci_ring_type type, unsigned int max_packet, gfp_t flags)
+static struct xhci_ring *
+xhci_ring_alloc_from_pool(struct xhci_hcd *xhci, unsigned int num_segs,
+ enum xhci_ring_type type, unsigned int max_packet,
+ struct dma_pool *pool, gfp_t flags)
{
struct xhci_ring *ring;
int ret;
@@ -382,6 +381,7 @@ struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci, unsigned int num_segs,
ring->num_segs = num_segs;
ring->bounce_buf_len = max_packet;
+ ring->segment_pool = pool;
INIT_LIST_HEAD(&ring->td_list);
ring->type = type;
if (num_segs == 0)
@@ -398,6 +398,20 @@ struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci, unsigned int num_segs,
return NULL;
}
+/*
+ * Create a new ring with zero or more segments.
+ *
+ * Link each segment together into a ring.
+ * Set the end flag and the cycle toggle bit on the last segment.
+ * See section 4.9.1 and figures 15 and 16.
+ */
+struct xhci_ring *xhci_ring_alloc(struct xhci_hcd *xhci, unsigned int num_segs,
+ enum xhci_ring_type type, unsigned int max_packet, gfp_t flags)
+{
+ return xhci_ring_alloc_from_pool(xhci, num_segs, type, max_packet,
+ xhci->segment_pool, flags);
+}
+
void xhci_free_endpoint_ring(struct xhci_hcd *xhci,
struct xhci_virt_device *virt_dev,
unsigned int ep_index)
@@ -422,6 +436,7 @@ int xhci_ring_expansion(struct xhci_hcd *xhci, struct xhci_ring *ring,
new_ring.num_segs = num_new_segs;
new_ring.bounce_buf_len = ring->bounce_buf_len;
new_ring.type = ring->type;
+ new_ring.segment_pool = ring->segment_pool;
ret = xhci_alloc_segments_for_ring(xhci, &new_ring, flags);
if (ret)
return -ENOMEM;
@@ -1424,6 +1439,7 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
unsigned int mult;
unsigned int avg_trb_len;
unsigned int err_count = 0;
+ struct dma_pool *pool;
ep_index = xhci_get_endpoint_index(&ep->desc);
ep_ctx = xhci_get_ep_ctx(xhci, virt_dev->in_ctx, ep_index);
@@ -1487,8 +1503,10 @@ int xhci_endpoint_init(struct xhci_hcd *xhci,
avg_trb_len = 8;
/* Set up the endpoint ring */
+ pool = virt_dev->eps[ep_index].sideband ?
+ virt_dev->eps[ep_index].sideband->segment_pool : xhci->segment_pool;
virt_dev->eps[ep_index].new_ring =
- xhci_ring_alloc(xhci, 2, ring_type, max_packet, mem_flags);
+ xhci_ring_alloc_from_pool(xhci, 2, ring_type, max_packet, pool, mem_flags);
if (!virt_dev->eps[ep_index].new_ring)
return -ENOMEM;
@@ -2291,7 +2309,8 @@ static int xhci_setup_port_arrays(struct xhci_hcd *xhci, gfp_t flags)
}
static struct xhci_interrupter *
-xhci_alloc_interrupter(struct xhci_hcd *xhci, unsigned int segs, gfp_t flags)
+xhci_alloc_interrupter(struct xhci_hcd *xhci, unsigned int segs,
+ struct dma_pool *pool, gfp_t flags)
{
struct device *dev = xhci_to_hcd(xhci)->self.sysdev;
struct xhci_interrupter *ir;
@@ -2308,7 +2327,7 @@ xhci_alloc_interrupter(struct xhci_hcd *xhci, unsigned int segs, gfp_t flags)
if (!ir)
return NULL;
- ir->event_ring = xhci_ring_alloc(xhci, segs, TYPE_EVENT, 0, flags);
+ ir->event_ring = xhci_ring_alloc_from_pool(xhci, segs, TYPE_EVENT, 0, pool, flags);
if (!ir->event_ring) {
xhci_warn(xhci, "Failed to allocate interrupter event ring\n");
kfree(ir);
@@ -2356,7 +2375,8 @@ void xhci_add_interrupter(struct xhci_hcd *xhci, unsigned int intr_num)
struct xhci_interrupter *
xhci_create_secondary_interrupter(struct usb_hcd *hcd, unsigned int segs,
- u32 imod_interval, unsigned int intr_num)
+ struct dma_pool *pool, u32 imod_interval,
+ unsigned int intr_num)
{
struct xhci_hcd *xhci = hcd_to_xhci(hcd);
struct xhci_interrupter *ir;
@@ -2367,7 +2387,7 @@ xhci_create_secondary_interrupter(struct usb_hcd *hcd, unsigned int segs,
intr_num >= xhci->max_interrupters)
return NULL;
- ir = xhci_alloc_interrupter(xhci, segs, GFP_KERNEL);
+ ir = xhci_alloc_interrupter(xhci, segs, pool, GFP_KERNEL);
if (!ir)
return NULL;
@@ -2498,7 +2518,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
if (!xhci->interrupters)
goto fail;
- xhci->interrupters[0] = xhci_alloc_interrupter(xhci, 0, flags);
+ xhci->interrupters[0] = xhci_alloc_interrupter(xhci, 0, xhci->segment_pool, flags);
if (!xhci->interrupters[0])
goto fail;
diff --git a/drivers/usb/host/xhci-sideband.c b/drivers/usb/host/xhci-sideband.c
index 1585c47720e0..ec7d3859771c 100644
--- a/drivers/usb/host/xhci-sideband.c
+++ b/drivers/usb/host/xhci-sideband.c
@@ -10,6 +10,7 @@
#include <linux/usb/xhci-sideband.h>
#include <linux/dma-direct.h>
+#include <linux/dmapool.h>
#include "xhci.h"
@@ -342,8 +343,8 @@ xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
return -EBUSY;
sb->ir = xhci_create_secondary_interrupter(xhci_to_hcd(sb->xhci),
- num_seg, imod_interval,
- intr_num);
+ num_seg, sb->segment_pool,
+ imod_interval, intr_num);
if (!sb->ir)
return -ENOMEM;
@@ -397,6 +398,11 @@ EXPORT_SYMBOL_GPL(xhci_sideband_interrupter_id);
/**
* xhci_sideband_register - register a sideband for a usb device
* @intf: usb interface associated with the sideband device
+ * @type: xHCI sideband type
+ * @segment_pool: dma pool for sideband ring segments, created and owned by
+ * the caller. The caller must destroy it after calling
+ * xhci_sideband_unregister().
+ * @notify_client: callback for xHCI sideband sequences
*
* Allows for clients to utilize XHCI interrupters and fetch transfer and event
* ring parameters for executing data transfers.
@@ -405,6 +411,7 @@ EXPORT_SYMBOL_GPL(xhci_sideband_interrupter_id);
*/
struct xhci_sideband *
xhci_sideband_register(struct usb_interface *intf, enum xhci_sideband_type type,
+ struct dma_pool *segment_pool,
int (*notify_client)(struct usb_interface *intf,
struct xhci_sideband_event *evt))
{
@@ -426,6 +433,8 @@ xhci_sideband_register(struct usb_interface *intf, enum xhci_sideband_type type,
if (!sb)
return NULL;
+ sb->segment_pool = segment_pool;
+
mutex_init(&sb->mutex);
/* check this device isn't already controlled via sideband */
@@ -450,6 +459,7 @@ xhci_sideband_register(struct usb_interface *intf, enum xhci_sideband_type type,
spin_unlock_irq(&xhci->lock);
+
return sb;
}
EXPORT_SYMBOL_GPL(xhci_sideband_register);
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index c7bfa7f028d3..c91cba16abea 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -19,6 +19,7 @@
#include <linux/usb/hcd.h>
#include <linux/io-64-nonatomic-lo-hi.h>
#include <linux/io-64-nonatomic-hi-lo.h>
+#include <linux/usb/xhci-sideband.h>
/* Code sharing between pci-quirks and xhci hcd */
#include "xhci-ext-caps.h"
@@ -738,8 +739,6 @@ struct xhci_interval_bw_table {
unsigned int ss_bw_out;
};
-#define EP_CTX_PER_DEV 31
-
struct xhci_virt_device {
int slot_id;
struct usb_device *udev;
@@ -1253,14 +1252,11 @@ static inline const char *xhci_trb_type_string(u8 type)
#define NEC_FW_MAJOR(p) (((p) >> 8) & 0xff)
/*
- * TRBS_PER_SEGMENT must be a multiple of 4,
- * since the command ring is 64-byte aligned.
- * It must also be greater than 16.
+ * TRBS_PER_SEGMENT and TRB_SEGMENT_SIZE are defined in
+ * <linux/usb/xhci-sideband.h>, shared with sideband client drivers.
*/
-#define TRBS_PER_SEGMENT 256
/* Allow two commands + a link TRB, along with any reserved command TRBs */
#define MAX_RSVD_CMD_TRBS (TRBS_PER_SEGMENT - 3)
-#define TRB_SEGMENT_SIZE (TRBS_PER_SEGMENT*16)
#define TRB_SEGMENT_SHIFT (ilog2(TRB_SEGMENT_SIZE))
/* TRB buffer pointers can't cross 64KB boundaries */
#define TRB_MAX_BUFF_SHIFT 16
@@ -1380,6 +1376,7 @@ struct xhci_ring {
enum xhci_ring_type type;
u32 old_trb_comp_code;
struct radix_tree_root *trb_address_map;
+ struct dma_pool *segment_pool;
};
struct xhci_erst_entry {
@@ -1865,7 +1862,8 @@ void xhci_free_port_bw_ctx(struct xhci_hcd *xhci,
struct xhci_container_ctx *ctx);
struct xhci_interrupter *
xhci_create_secondary_interrupter(struct usb_hcd *hcd, unsigned int segs,
- u32 imod_interval, unsigned int intr_num);
+ struct dma_pool *pool, u32 imod_interval,
+ unsigned int intr_num);
void xhci_remove_secondary_interrupter(struct usb_hcd
*hcd, struct xhci_interrupter *ir);
void xhci_skip_sec_intr_events(struct xhci_hcd *xhci,
diff --git a/include/linux/usb/xhci-sideband.h b/include/linux/usb/xhci-sideband.h
index 005257085dcb..338146674a88 100644
--- a/include/linux/usb/xhci-sideband.h
+++ b/include/linux/usb/xhci-sideband.h
@@ -13,7 +13,19 @@
#include <linux/usb.h>
#include <linux/usb/hcd.h>
-#define EP_CTX_PER_DEV 31 /* FIXME defined twice, from xhci.h */
+/*
+ * Constants shared with the xHCI host driver (drivers/usb/host/xhci.h),
+ * which includes this header for its canonical definitions.
+ */
+#define EP_CTX_PER_DEV 31
+
+/*
+ * TRBS_PER_SEGMENT must be a multiple of 4,
+ * since the command ring is 64-byte aligned.
+ * It must also be greater than 16.
+ */
+#define TRBS_PER_SEGMENT 256
+#define TRB_SEGMENT_SIZE (TRBS_PER_SEGMENT * 16)
struct xhci_sideband;
@@ -59,6 +71,13 @@ struct xhci_sideband {
/* Synchronizing xHCI sideband operations with client drivers operations */
struct mutex mutex;
+ /*
+ * Separate sideband segment pool for sideband rings, supplied by and
+ * owned by the sideband client: created before xhci_sideband_register()
+ * and destroyed after xhci_sideband_unregister().
+ */
+ struct dma_pool *segment_pool;
+
struct usb_interface *intf;
int (*notify_client)(struct usb_interface *intf,
struct xhci_sideband_event *evt);
@@ -66,6 +85,7 @@ struct xhci_sideband {
struct xhci_sideband *
xhci_sideband_register(struct usb_interface *intf, enum xhci_sideband_type type,
+ struct dma_pool *segment_pool,
int (*notify_client)(struct usb_interface *intf,
struct xhci_sideband_event *evt));
void
diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
index e4bfd43a2488..1b8877b8ee62 100644
--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -7,6 +7,7 @@
#include <linux/ctype.h>
#include <linux/dma-mapping.h>
#include <linux/dma-map-ops.h>
+#include <linux/dmapool.h>
#include <linux/init.h>
#include <linux/iommu.h>
#include <linux/module.h>
@@ -1786,6 +1787,7 @@ static void qc_usb_audio_offload_probe(struct snd_usb_audio *chip)
struct usb_interface_descriptor *altsd;
struct usb_host_interface *alts;
struct snd_soc_usb_device *sdev;
+ struct dma_pool *segment_pool;
struct xhci_sideband *sb;
/*
@@ -1804,10 +1806,19 @@ static void qc_usb_audio_offload_probe(struct snd_usb_audio *chip)
if (!sdev)
return;
- sb = xhci_sideband_register(intf, XHCI_SIDEBAND_VENDOR,
+ segment_pool = dma_pool_create("xHCI sideband ring segments",
+ interface_to_usbdev(intf)->bus->sysdev,
+ TRB_SEGMENT_SIZE, TRB_SEGMENT_SIZE,
+ TRB_SEGMENT_SIZE);
+ if (!segment_pool)
+ goto free_sdev;
+
+ sb = xhci_sideband_register(intf, XHCI_SIDEBAND_VENDOR, segment_pool,
uaudio_sideband_notifier);
- if (!sb)
+ if (!sb) {
+ dma_pool_destroy(segment_pool);
goto free_sdev;
+ }
} else {
sb = uadev[chip->card->number].sb;
sdev = uadev[chip->card->number].sdev;
@@ -1844,7 +1855,9 @@ static void qc_usb_audio_offload_probe(struct snd_usb_audio *chip)
return;
unreg_xhci:
+ segment_pool = sb->segment_pool;
xhci_sideband_unregister(sb);
+ dma_pool_destroy(segment_pool);
uadev[chip->card->number].sb = NULL;
free_sdev:
kfree(sdev);
@@ -1905,8 +1918,12 @@ static void qc_usb_audio_offload_disconnect(struct snd_usb_audio *chip)
* This is to accommodate for devices w/ multiple UAC functions.
*/
if (chip->num_interfaces == 1) {
+ struct dma_pool *segment_pool = dev->sb->segment_pool;
+
snd_soc_usb_disconnect(uaudio_qdev->auxdev->dev.parent, dev->sdev);
xhci_sideband_unregister(dev->sb);
+ dma_pool_destroy(segment_pool);
+ dev->sb = NULL;
dev->chip = NULL;
kfree(dev->sdev->ppcm_idx);
kfree(dev->sdev);
--
2.34.1