soundwire: use bra if msg size > threshold in sdw_nread/write_no_pm by bardliao · Pull Request #5811 · thesofproject/linux

bardliao · 2026-06-11T14:38:43Z

It is more efficient to read/write with bra if the message size is
larger than a predefined threshold. The threshold can be set by
the caller of sdw_bus_master_add().

Copilot

Pull request overview

Note

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This PR introduces configurable thresholds for switching SoundWire register transfers to a BPT-based path and adds an early-boot guard for SOF BPT open.

Changes:

Add bra_w_threshold / bra_r_threshold fields to struct sdw_bus and initialize defaults on master add.
Route sdw_nread_no_pm() / sdw_nwrite_no_pm() through a new BPT transfer helper for larger transfers.
Gate hda_sdw_bpt_open() when SOF firmware boot is not complete (non-DSPless, first boot).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
sound/soc/sof/intel/hda-sdw-bpt.c	Adds a boot-completion guard before preparing BPT DMA.
include/linux/soundwire/sdw.h	Extends `sdw_bus` with BRA threshold configuration fields and updates kernel-doc.
drivers/soundwire/bus.c	Adds default BRA thresholds and implements BPT-based nread/nwrite fast path.

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Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

 * Note that if the message crosses a page boundary each page will be
 * transferred under a separate invocation of the msg_lock.
 */


 * Note that if the message crosses a page boundary each page will be
 * transferred under a separate invocation of the msg_lock.
 */


Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

On Intel ACE2+ platforms, each SoundWire link uses a single pair of PDIs (PDI0 for TX, PDI1 for RX) and associated DMA resources for Bulk Port Transfers. When two codecs on the same link initiate BRA transfers concurrently (e.g. during firmware download), the second sdw_bpt_send_async() call races with the first: - intel_ace2x_bpt_open_stream() has a TOCTOU on the bpt_stream pointer: both callers see it as NULL and proceed - The second open overwrites the first's stream allocation, leaking the original sdw_stream_runtime - PCMSyCM mappings for the first transfer get overwritten, causing chain DMA to operate with wrong PDI assignments - IOC timeouts, use-after-free, and double-free follow on close Add a per-bus bpt_lock mutex held across the send_async/wait span to serialize BPT transfers. The lock is acquired in sdw_bpt_send_async() before calling the master ops and released in sdw_bpt_wait() after the transfer completes. On send_async failure, the lock is released immediately. Cross-link transfers (different sdw_bus instances) remain concurrent since each bus has its own lock. Signed-off-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>

The BPT stream needs SOF DSP's support. We can only open a BPT stream after the SOF DSP FW is downloaded and booted completed. It also doesn't make sense to wait for SOF FW boot instead of starting common read/write immediately. Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 8 comments.

bardliao · 2026-06-12T10:05:49Z

 int sdw_nwrite_no_pm(struct sdw_slave *slave, u32 addr, size_t count, const u8 *val)
 {
+	struct sdw_bus *bus = slave->bus;
+	int ret;
+
+	if (!bus->ops->bpt_send_async || !bus->ops->bpt_wait ||
+	    count < bus->bra_w_threshold)
+		goto fallback;
+
+	ret = sdw_ntransfer_no_pm_bpt(slave, addr, SDW_MSG_FLAG_WRITE, count, (u8 *)val);
+	if (!ret)
+		return 0;
+
+	dev_dbg(&slave->dev,
+		"BPT write failed for addr %x, count %zu, ret %d fallback to normal write\n",
+		addr, count, ret);
+fallback:
 	return sdw_ntransfer_no_pm(slave, addr, SDW_MSG_FLAG_WRITE, count, (u8 *)val);
 }


@charleskeepax @rfvirgil @simontrimmer @shumingfan Will it cause any issue?

bardliao · 2026-06-12T11:19:40Z

 int sdw_bpt_send_async(struct sdw_bus *bus, struct sdw_slave *slave, struct sdw_bpt_msg *msg)
 {
 	int len = 0;
+	int ret;
 	int i;


We unlock the mutex when sdw_bpt_send_async, too. It should be fine. @ujfalusi What do you think?

bardliao · 2026-06-12T11:20:20Z

+	/* Serialize BPT/BRA transfers per bus: PDIs and DMA resources are shared */
+	mutex_lock(&bus->bpt_lock);
+
+	ret = bus->ops->bpt_send_async(bus, slave, msg);
+	if (ret < 0)
+		mutex_unlock(&bus->bpt_lock);
+
+	/* on success the lock is held until sdw_bpt_wait() */
+	return ret;
 }
 EXPORT_SYMBOL(sdw_bpt_send_async);

 int sdw_bpt_wait(struct sdw_bus *bus, struct sdw_slave *slave, struct sdw_bpt_msg *msg)
 {
-	return bus->ops->bpt_wait(bus, slave, msg);
+	int ret;
+
+	ret = bus->ops->bpt_wait(bus, slave, msg);
+	mutex_unlock(&bus->bpt_lock);
+
+	return ret;
 }


Same as the previous comment

+#define DEFAULT_BRA_WRITE_THRESHOLD	800
+#define DEFAULT_BRA_READ_THRESHOLD	400


+	if (!bus->bra_w_threshold)
+		bus->bra_w_threshold = DEFAULT_BRA_WRITE_THRESHOLD;
+	if (!bus->bra_r_threshold)
+		bus->bra_r_threshold = DEFAULT_BRA_READ_THRESHOLD;


We need a threshold to use BRA. The threshold can be set in the bus struct when sdw_bus_master_add() is called. Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

It is more efficient to read/write with bra if the message size is larger than a predefined threshold. Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

+ * @bra_w_threshold: Message-size threshold (bytes) above which BPT write is used.
+ * If set to 0, a default is used.
+ * @bra_r_threshold: Message-size threshold (bytes) above which BPT read is used.
+ * If set to 0, a default is used.


+fallback:
 	return sdw_ntransfer_no_pm(slave, addr, SDW_MSG_FLAG_WRITE, count, (u8 *)val);


bardliao requested review from charleskeepax, Copilot, plbossart, rfvirgil, shumingfan, simontrimmer and ujfalusi June 11, 2026 14:38

Copilot started reviewing on behalf of bardliao June 11, 2026 14:38 View session

Copilot stopped reviewing on behalf of bardliao due to an error June 11, 2026 14:41
An unexpected error occurred. For more details, see the detailed logs in GitHub Actions.

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Comment thread drivers/soundwire/bus.c Outdated

Comment thread drivers/soundwire/bus.c Outdated

Comment thread drivers/soundwire/bus.c

Comment thread include/linux/soundwire/sdw.h Outdated

Comment thread sound/soc/sof/intel/hda-sdw-bpt.c

bardliao force-pushed the pr-move-bra-to-sdw-bus branch 3 times, most recently from 1bad5a1 to f490794 Compare June 12, 2026 02:51

bardliao requested a review from Copilot June 12, 2026 02:55

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Comment thread drivers/soundwire/bus.c

Comment thread drivers/soundwire/bus.c

Comment thread include/linux/soundwire/sdw.h Outdated

bardliao force-pushed the pr-move-bra-to-sdw-bus branch 2 times, most recently from bffe82b to 2315a97 Compare June 12, 2026 04:47

bardliao requested a review from Copilot June 12, 2026 04:48

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bardliao force-pushed the pr-move-bra-to-sdw-bus branch 2 times, most recently from 0da207e to b73e001 Compare June 12, 2026 06:11

bardliao requested a review from Copilot June 12, 2026 06:11

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Comment thread drivers/soundwire/bus.c

Comment thread drivers/soundwire/bus.c

bardliao force-pushed the pr-move-bra-to-sdw-bus branch from b73e001 to 3a35af3 Compare June 12, 2026 06:33

ujfalusi and others added 2 commits June 12, 2026 17:26

bardliao force-pushed the pr-move-bra-to-sdw-bus branch from 3a35af3 to c8a1f52 Compare June 12, 2026 09:42

bardliao requested a review from Copilot June 12, 2026 09:44

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Copilot started reviewing on behalf of bardliao June 12, 2026 10:24 View session

bardliao added 2 commits June 12, 2026 19:14

soundwire: bus: add bra_w/r_threshold

861c55b

We need a threshold to use BRA. The threshold can be set in the bus struct when sdw_bus_master_add() is called. Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

soundwire: use bra if msg size > threshold

4e63a29

It is more efficient to read/write with bra if the message size is larger than a predefined threshold. Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>

bardliao force-pushed the pr-move-bra-to-sdw-bus branch from c8a1f52 to 4e63a29 Compare June 12, 2026 11:18

bardliao requested a review from Copilot June 12, 2026 11:20

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		#define DEFAULT_BRA_WRITE_THRESHOLD 800
		#define DEFAULT_BRA_READ_THRESHOLD 400

		fallback:
		return sdw_ntransfer_no_pm(slave, addr, SDW_MSG_FLAG_WRITE, count, (u8 *)val);

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