* [PATCH v3 1/3] bus: mhi: host: clients: Add loopback driver with sysfs interface
2026-06-10 5:52 [PATCH v3 0/3] bus: mhi: Add loopback driver Sumit Kumar
@ 2026-06-10 5:52 ` Sumit Kumar
2026-06-10 5:52 ` [PATCH v3 2/3] bus: mhi: ep: Add mhi_ep_queue_buf() API for raw buffer queuing Sumit Kumar
2026-06-10 5:52 ` [PATCH v3 3/3] bus: mhi: ep: clients: Add loopback driver for data path testing Sumit Kumar
2 siblings, 0 replies; 4+ messages in thread
From: Sumit Kumar @ 2026-06-10 5:52 UTC (permalink / raw)
To: Manivannan Sadhasivam
Cc: mhi, linux-arm-msm, linux-kernel, Sumit Kumar, Krishna Chaitanya Chundru
The MHI specification defines a LOOPBACK channel. The endpoint firmware
echoes back whatever the host sends on this channel. Without a host-side
driver, there is no way to exercise this channel to validate MHI data path
integrity between host and endpoint.
Add a host-side loopback driver that binds to the LOOPBACK channel and
expose a sysfs interface for data path testing. The sysfs interface allows
users to configure TRE buffer size and count, trigger a loopback test, and
read the result.
Co-developed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Sumit Kumar <sumit.kumar@oss.qualcomm.com>
---
.../ABI/testing/sysfs-bus-mhi-devices-loopback | 51 ++++
MAINTAINERS | 1 +
drivers/bus/mhi/host/Kconfig | 1 +
drivers/bus/mhi/host/Makefile | 1 +
drivers/bus/mhi/host/clients/Kconfig | 17 ++
drivers/bus/mhi/host/clients/Makefile | 2 +
drivers/bus/mhi/host/clients/loopback.c | 316 +++++++++++++++++++++
7 files changed, 389 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-bus-mhi-devices-loopback b/Documentation/ABI/testing/sysfs-bus-mhi-devices-loopback
new file mode 100644
index 0000000000000000000000000000000000000000..3bd770747799a3341a23903cc1a108e650e915b8
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-mhi-devices-loopback
@@ -0,0 +1,51 @@
+What: /sys/bus/mhi/devices/mhi<N>_LOOPBACK/tre_size
+Date: April 2026
+KernelVersion: 7.1
+Contact: mhi@lists.linux.dev
+Description:
+ (RW) Size of each Transfer Ring Element (TRE) buffer in bytes
+ used for the loopback test. Valid range is 1 to the value
+ reported by max_tre_size. Default value is 32 bytes.
+
+What: /sys/bus/mhi/devices/mhi<N>_LOOPBACK/max_tre_size
+Date: April 2026
+KernelVersion: 7.1
+Contact: mhi@lists.linux.dev
+Description:
+ (RO) Maximum allowed TRE size in bytes. Reading this file
+ returns the upper bound for the tre_size attribute.
+
+What: /sys/bus/mhi/devices/mhi<N>_LOOPBACK/num_tre
+Date: April 2026
+KernelVersion: 7.1
+Contact: mhi@lists.linux.dev
+Description:
+ (RW) Number of Transfer Ring Elements (TREs) to use per
+ loopback test. Must be greater than zero and must not exceed
+ the channel ring capacity. Default value is 1.
+
+What: /sys/bus/mhi/devices/mhi<N>_LOOPBACK/start
+Date: April 2026
+KernelVersion: 7.1
+Contact: mhi@lists.linux.dev
+Description:
+ (WO) Write any value to trigger a loopback test. The driver
+ sends random data to the endpoint using the configured tre_size
+ and num_tre parameters, waits for the endpoint to echo it back,
+ and verifies the received data matches what was sent.
+
+ This is a blocking write that returns when the test completes
+ or times out after 5 seconds.
+
+What: /sys/bus/mhi/devices/mhi<N>_LOOPBACK/status
+Date: April 2026
+KernelVersion: 7.1
+Contact: mhi@lists.linux.dev
+Description:
+ (RO) Result of the last loopback test. Returns one of:
+ "pass" - last test completed successfully
+ "fail" - last test failed
+ "not started" - no test has been run yet
+
+ Reading this file while a test is in progress will block
+ until the test completes.
diff --git a/MAINTAINERS b/MAINTAINERS
index 6dcfbd11efef87927041f5cf58d70633dbb4b18d..ff12a6da48947ac853bc638359a7046fea85fc21 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16441,6 +16441,7 @@ L: linux-arm-msm@vger.kernel.org
S: Maintained
T: git git://git.kernel.org/pub/scm/linux/kernel/git/mani/mhi.git
F: Documentation/ABI/stable/sysfs-bus-mhi
+F: Documentation/ABI/testing/sysfs-bus-mhi-devices-loopback
F: Documentation/mhi/
F: drivers/bus/mhi/
F: drivers/pci/endpoint/functions/pci-epf-mhi.c
diff --git a/drivers/bus/mhi/host/Kconfig b/drivers/bus/mhi/host/Kconfig
index da5cd0c9fc620ab595e742c422f1a22a2a84c7b9..627c57948235aa52348179ae8b2d0826ebaed01e 100644
--- a/drivers/bus/mhi/host/Kconfig
+++ b/drivers/bus/mhi/host/Kconfig
@@ -29,3 +29,4 @@ config MHI_BUS_PCI_GENERIC
This driver provides MHI PCI controller driver for devices such as
Qualcomm SDX55 based PCIe modems.
+source "drivers/bus/mhi/host/clients/Kconfig"
diff --git a/drivers/bus/mhi/host/Makefile b/drivers/bus/mhi/host/Makefile
index 859c2f38451c669b3d3014c374b2b957c99a1cfe..2a16008aeb38127494782bbff4e1656428d2b776 100644
--- a/drivers/bus/mhi/host/Makefile
+++ b/drivers/bus/mhi/host/Makefile
@@ -4,3 +4,4 @@ mhi-$(CONFIG_MHI_BUS_DEBUG) += debugfs.o
obj-$(CONFIG_MHI_BUS_PCI_GENERIC) += mhi_pci_generic.o
mhi_pci_generic-y += pci_generic.o
+obj-y += clients/
diff --git a/drivers/bus/mhi/host/clients/Kconfig b/drivers/bus/mhi/host/clients/Kconfig
new file mode 100644
index 0000000000000000000000000000000000000000..d1463c3e0df0da461c815afaec623ba349b51dda
--- /dev/null
+++ b/drivers/bus/mhi/host/clients/Kconfig
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config MHI_BUS_LOOPBACK
+ tristate "MHI LOOPBACK client driver"
+ depends on MHI_BUS
+ help
+ MHI LOOPBACK client driver that binds to the MHI LOOPBACK channel
+ as defined in the MHI specification. The LOOPBACK channel is
+ implemented by MHI-based devices (modems, WLAN) in the field, where
+ the endpoint firmware echoes back whatever the host sends.
+
+ This driver exposes a sysfs interface for testing MHI data path
+ integrity between host and endpoint. Users can configure the TRE
+ size and count, trigger a loopback test, and read the result.
+
+ To compile this driver as a module, choose M here. The module
+ will be called mhi_loopback.
diff --git a/drivers/bus/mhi/host/clients/Makefile b/drivers/bus/mhi/host/clients/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..3811b6928f42b38f94b1167941cf3b0fe512d32b
--- /dev/null
+++ b/drivers/bus/mhi/host/clients/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_MHI_BUS_LOOPBACK) += mhi_loopback.o
+mhi_loopback-y += loopback.o
diff --git a/drivers/bus/mhi/host/clients/loopback.c b/drivers/bus/mhi/host/clients/loopback.c
new file mode 100644
index 0000000000000000000000000000000000000000..3ae4d94dbc6b291006bb206ec40a634ae9561f5d
--- /dev/null
+++ b/drivers/bus/mhi/host/clients/loopback.c
@@ -0,0 +1,316 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+/*
+ * The MHI LOOPBACK channel is defined in the MHI specification and is
+ * implemented by MHI-based devices (modems, WLAN) already deployed in the
+ * field. The endpoint firmware echoes back whatever the host sends on this
+ * channel. This driver binds to the LOOPBACK channel and exposes a sysfs
+ * interface for testing MHI data path integrity between host and endpoint.
+ * The sysfs interface is stable ABI because the wire protocol is fixed by
+ * the endpoint firmware and cannot be changed.
+ */
+
+#include <linux/atomic.h>
+#include <linux/completion.h>
+#include <linux/errno.h>
+#include <linux/mhi.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/random.h>
+#include <linux/sizes.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/types.h>
+
+#define MHI_LOOPBACK_DEFAULT_TRE_SIZE 32
+#define MHI_LOOPBACK_DEFAULT_NUM_TRE 1
+#define MHI_LOOPBACK_TIMEOUT_MS 5000
+#define MHI_LOOPBACK_MAX_TRE_SIZE SZ_64K
+
+struct mhi_loopback {
+ struct mhi_device *mdev;
+ struct mutex lb_mutex; /* serializes concurrent test operations */
+ struct completion comp;
+ atomic_t tres_pending; /* DL callbacks still outstanding */
+ const char *result;
+ u32 num_tre;
+ u32 tre_size;
+};
+
+static ssize_t tre_size_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(dev);
+
+ return sysfs_emit(buf, "%u\n", loopback->tre_size);
+}
+
+static ssize_t tre_size_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(dev);
+ u32 val;
+
+ if (kstrtou32(buf, 0, &val))
+ return -EINVAL;
+
+ if (val == 0 || val > MHI_LOOPBACK_MAX_TRE_SIZE)
+ return -EINVAL;
+
+ guard(mutex)(&loopback->lb_mutex);
+ loopback->tre_size = val;
+
+ return count;
+}
+static DEVICE_ATTR_RW(tre_size);
+
+static ssize_t max_tre_size_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%u\n", MHI_LOOPBACK_MAX_TRE_SIZE);
+}
+static DEVICE_ATTR_RO(max_tre_size);
+
+static ssize_t num_tre_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(dev);
+
+ return sysfs_emit(buf, "%u\n", loopback->num_tre);
+}
+
+static ssize_t num_tre_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(dev);
+ u32 val;
+ int el_num;
+
+ if (kstrtou32(buf, 0, &val))
+ return -EINVAL;
+
+ if (val == 0)
+ return -EINVAL;
+
+ guard(mutex)(&loopback->lb_mutex);
+
+ el_num = mhi_get_free_desc_count(loopback->mdev, DMA_TO_DEVICE);
+ if (val > el_num) {
+ dev_err(dev, "num_tre (%u) exceeds ring capacity (%d)\n", val, el_num);
+ return -EINVAL;
+ }
+
+ loopback->num_tre = val;
+
+ return count;
+}
+static DEVICE_ATTR_RW(num_tre);
+
+static ssize_t start_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(dev);
+ void *send_buf = NULL, *recv_buf = NULL;
+ u32 total_size, tre_count, tre_size;
+ ssize_t ret;
+ int i;
+
+ guard(mutex)(&loopback->lb_mutex);
+
+ tre_size = loopback->tre_size;
+ tre_count = loopback->num_tre;
+ total_size = size_mul(tre_count, tre_size);
+
+ recv_buf = kzalloc(total_size, GFP_KERNEL);
+ if (!recv_buf)
+ return -ENOMEM;
+
+ send_buf = kzalloc(total_size, GFP_KERNEL);
+ if (!send_buf) {
+ ret = -ENOMEM;
+ goto free_buf;
+ }
+
+ ret = mhi_prepare_for_transfer(loopback->mdev);
+ if (ret) {
+ dev_err(dev, "failed to prepare for transfers: %zd\n", ret);
+ goto free_buf;
+ }
+
+ get_random_bytes(send_buf, total_size);
+
+ /* Arm completion before queuing recv TREs to avoid losing an early callback */
+ atomic_set(&loopback->tres_pending, tre_count);
+ reinit_completion(&loopback->comp);
+
+ for (i = 0; i < tre_count; i++) {
+ ret = mhi_queue_buf(loopback->mdev, DMA_FROM_DEVICE,
+ recv_buf + (i * tre_size), tre_size, MHI_EOT);
+ if (ret) {
+ dev_err(dev, "Unable to queue read TRE %d: %zd\n", i, ret);
+ loopback->result = "fail";
+ if (atomic_sub_and_test(tre_count - i, &loopback->tres_pending))
+ complete(&loopback->comp);
+ goto out;
+ }
+ }
+
+ for (i = 0; i < tre_count - 1; i++) {
+ ret = mhi_queue_buf(loopback->mdev, DMA_TO_DEVICE,
+ send_buf + (i * tre_size), tre_size, MHI_CHAIN);
+ if (ret) {
+ dev_err(dev, "Unable to queue send TRE %d: %zd\n", i, ret);
+ loopback->result = "fail";
+ goto out;
+ }
+ }
+
+ ret = mhi_queue_buf(loopback->mdev, DMA_TO_DEVICE,
+ send_buf + (i * tre_size), tre_size, MHI_EOT);
+ if (ret) {
+ dev_err(dev, "Unable to queue final TRE: %zd\n", ret);
+ loopback->result = "fail";
+ goto out;
+ }
+
+ if (!wait_for_completion_timeout(&loopback->comp,
+ msecs_to_jiffies(MHI_LOOPBACK_TIMEOUT_MS))) {
+ dev_err(dev, "Loopback test timed out\n");
+ loopback->result = "fail";
+ ret = -ETIMEDOUT;
+ goto out;
+ }
+
+ if (memcmp(send_buf, recv_buf, total_size)) {
+ dev_err(dev, "Loopback data mismatch\n");
+ loopback->result = "fail";
+ ret = -EIO;
+ goto out;
+ }
+
+ loopback->result = "pass";
+ ret = count;
+
+out:
+ mhi_unprepare_from_transfer(loopback->mdev);
+free_buf:
+ kfree(send_buf);
+ kfree(recv_buf);
+ return ret;
+}
+static DEVICE_ATTR_WO(start);
+
+static ssize_t status_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(dev);
+
+ guard(mutex)(&loopback->lb_mutex);
+
+ return sysfs_emit(buf, "%s\n", loopback->result);
+}
+static DEVICE_ATTR_RO(status);
+
+static void mhi_loopback_dl_callback(struct mhi_device *mhi_dev,
+ struct mhi_result *mhi_res)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(&mhi_dev->dev);
+
+ if (!loopback)
+ return;
+
+ if (mhi_res->transaction_status && mhi_res->transaction_status != -ENOTCONN)
+ dev_err(&mhi_dev->dev, "DL callback error: status %d\n",
+ mhi_res->transaction_status);
+
+ if (atomic_dec_and_test(&loopback->tres_pending))
+ complete(&loopback->comp);
+}
+
+static void mhi_loopback_ul_callback(struct mhi_device *mhi_dev,
+ struct mhi_result *mhi_res)
+{
+}
+
+static struct attribute *mhi_loopback_attrs[] = {
+ &dev_attr_tre_size.attr,
+ &dev_attr_max_tre_size.attr,
+ &dev_attr_num_tre.attr,
+ &dev_attr_start.attr,
+ &dev_attr_status.attr,
+ NULL,
+};
+
+static const struct attribute_group mhi_loopback_group = {
+ .attrs = mhi_loopback_attrs,
+};
+
+static int mhi_loopback_probe(struct mhi_device *mhi_dev,
+ const struct mhi_device_id *id)
+{
+ struct mhi_loopback *loopback;
+ int rc;
+
+ loopback = devm_kzalloc(&mhi_dev->dev, sizeof(*loopback), GFP_KERNEL);
+ if (!loopback)
+ return -ENOMEM;
+
+ loopback->mdev = mhi_dev;
+ loopback->tre_size = MHI_LOOPBACK_DEFAULT_TRE_SIZE;
+ loopback->num_tre = MHI_LOOPBACK_DEFAULT_NUM_TRE;
+ loopback->result = "not started";
+
+ mutex_init(&loopback->lb_mutex);
+ init_completion(&loopback->comp);
+
+ dev_set_drvdata(&mhi_dev->dev, loopback);
+
+ rc = devm_device_add_group(&mhi_dev->dev, &mhi_loopback_group);
+ if (rc)
+ dev_err(&mhi_dev->dev, "failed to create sysfs attributes\n");
+
+ return rc;
+}
+
+static void mhi_loopback_remove(struct mhi_device *mhi_dev)
+{
+ struct mhi_loopback *loopback = dev_get_drvdata(&mhi_dev->dev);
+
+ complete(&loopback->comp);
+
+ mutex_lock(&loopback->lb_mutex);
+ mutex_unlock(&loopback->lb_mutex);
+
+ dev_set_drvdata(&mhi_dev->dev, NULL);
+}
+
+static const struct mhi_device_id mhi_loopback_id_table[] = {
+ { .chan = "LOOPBACK"},
+ {}
+};
+MODULE_DEVICE_TABLE(mhi, mhi_loopback_id_table);
+
+static struct mhi_driver mhi_loopback_driver = {
+ .probe = mhi_loopback_probe,
+ .remove = mhi_loopback_remove,
+ .dl_xfer_cb = mhi_loopback_dl_callback,
+ .ul_xfer_cb = mhi_loopback_ul_callback,
+ .id_table = mhi_loopback_id_table,
+ .driver = {
+ .name = "mhi_loopback",
+ },
+};
+
+module_mhi_driver(mhi_loopback_driver);
+
+MODULE_AUTHOR("Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>");
+MODULE_AUTHOR("Sumit Kumar <sumit.kumar@oss.qualcomm.com>");
+MODULE_DESCRIPTION("MHI Host Loopback Driver");
+MODULE_LICENSE("GPL");
--
2.34.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v3 2/3] bus: mhi: ep: Add mhi_ep_queue_buf() API for raw buffer queuing
2026-06-10 5:52 [PATCH v3 0/3] bus: mhi: Add loopback driver Sumit Kumar
2026-06-10 5:52 ` [PATCH v3 1/3] bus: mhi: host: clients: Add loopback driver with sysfs interface Sumit Kumar
@ 2026-06-10 5:52 ` Sumit Kumar
2026-06-10 5:52 ` [PATCH v3 3/3] bus: mhi: ep: clients: Add loopback driver for data path testing Sumit Kumar
2 siblings, 0 replies; 4+ messages in thread
From: Sumit Kumar @ 2026-06-10 5:52 UTC (permalink / raw)
To: Manivannan Sadhasivam; +Cc: mhi, linux-arm-msm, linux-kernel, Sumit Kumar
Some MHI endpoint clients do not use socket buffers and need a way to queue
raw buffers for DL transfers. Add mhi_ep_queue_buf() to support this use
case.
Refactor mhi_ep_queue_skb() to delegate to a new internal mhi_ep_queue()
helper shared by both APIs, and rename mhi_ep_skb_completion() to
mhi_ep_buf_completion() to reflect its broader use.
Signed-off-by: Sumit Kumar <sumit.kumar@oss.qualcomm.com>
---
drivers/bus/mhi/ep/main.c | 27 +++++++++++++++++++--------
include/linux/mhi_ep.h | 15 +++++++++++++++
2 files changed, 34 insertions(+), 8 deletions(-)
diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
index b3eafcf2a2c50d95e3efd3afb27038ecf55552a5..6c4c5ca473b821f9c2abe11cfe5043ec4c5545f4 100644
--- a/drivers/bus/mhi/ep/main.c
+++ b/drivers/bus/mhi/ep/main.c
@@ -516,7 +516,7 @@ static int mhi_ep_process_ch_ring(struct mhi_ep_ring *ring)
return 0;
}
-static void mhi_ep_skb_completion(struct mhi_ep_buf_info *buf_info)
+static void mhi_ep_buf_completion(struct mhi_ep_buf_info *buf_info)
{
struct mhi_ep_device *mhi_dev = buf_info->mhi_dev;
struct mhi_ep_cntrl *mhi_cntrl = mhi_dev->mhi_cntrl;
@@ -544,9 +544,9 @@ static void mhi_ep_skb_completion(struct mhi_ep_buf_info *buf_info)
mhi_ep_ring_inc_index(ring);
}
-
/* TODO: Handle partially formed TDs */
-int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
+static int mhi_ep_queue(struct mhi_ep_device *mhi_dev, void *buf, size_t len,
+ void *cb_buf)
{
struct mhi_ep_cntrl *mhi_cntrl = mhi_dev->mhi_cntrl;
struct mhi_ep_chan *mhi_chan = mhi_dev->dl_chan;
@@ -559,7 +559,7 @@ int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
u32 tre_len;
int ret;
- buf_left = skb->len;
+ buf_left = len;
ring = &mhi_cntrl->mhi_chan[mhi_chan->chan].ring;
mutex_lock(&mhi_chan->lock);
@@ -582,13 +582,13 @@ int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
tre_len = MHI_TRE_DATA_GET_LEN(el);
tr_len = min(buf_left, tre_len);
- read_offset = skb->len - buf_left;
+ read_offset = len - buf_left;
- buf_info.dev_addr = skb->data + read_offset;
+ buf_info.dev_addr = buf + read_offset;
buf_info.host_addr = MHI_TRE_DATA_GET_PTR(el);
buf_info.size = tr_len;
- buf_info.cb = mhi_ep_skb_completion;
- buf_info.cb_buf = skb;
+ buf_info.cb = mhi_ep_buf_completion;
+ buf_info.cb_buf = cb_buf;
buf_info.mhi_dev = mhi_dev;
/*
@@ -627,8 +627,19 @@ int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
return ret;
}
+
+int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
+{
+ return mhi_ep_queue(mhi_dev, skb->data, skb->len, skb);
+}
EXPORT_SYMBOL_GPL(mhi_ep_queue_skb);
+int mhi_ep_queue_buf(struct mhi_ep_device *mhi_dev, void *buf, size_t len)
+{
+ return mhi_ep_queue(mhi_dev, buf, len, buf);
+}
+EXPORT_SYMBOL_GPL(mhi_ep_queue_buf);
+
static int mhi_ep_cache_host_cfg(struct mhi_ep_cntrl *mhi_cntrl)
{
size_t cmd_ctx_host_size, ch_ctx_host_size, ev_ctx_host_size;
diff --git a/include/linux/mhi_ep.h b/include/linux/mhi_ep.h
index 7b40fc8cbe77ab8419d167e89264b69a817b9fb1..59f796e56207aaf8be09edc9ba4d1f59b665581f 100644
--- a/include/linux/mhi_ep.h
+++ b/include/linux/mhi_ep.h
@@ -302,4 +302,19 @@ bool mhi_ep_queue_is_empty(struct mhi_ep_device *mhi_dev, enum dma_data_directio
*/
int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb);
+/**
+ * mhi_ep_queue_buf - Send buffer to host over MHI Endpoint
+ * @mhi_dev: Device associated with the DL channel
+ * @buf: Buffer to be queued. On success, ownership passes to the MHI stack;
+ * the caller must not free @buf until the DL transfer callback fires
+ * with result->buf_addr equal to @buf. On failure, the caller retains
+ * ownership and must free @buf.
+ * Note: if @len spans multiple host DL TREs, the DL transfer callback
+ * fires once per TRE, each time with result->buf_addr equal to @buf.
+ * @len: Size of the buffer
+ *
+ * Return: 0 if the buffer has been sent successfully, a negative error code otherwise.
+ */
+int mhi_ep_queue_buf(struct mhi_ep_device *mhi_dev, void *buf, size_t len);
+
#endif
--
2.34.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v3 3/3] bus: mhi: ep: clients: Add loopback driver for data path testing
2026-06-10 5:52 [PATCH v3 0/3] bus: mhi: Add loopback driver Sumit Kumar
2026-06-10 5:52 ` [PATCH v3 1/3] bus: mhi: host: clients: Add loopback driver with sysfs interface Sumit Kumar
2026-06-10 5:52 ` [PATCH v3 2/3] bus: mhi: ep: Add mhi_ep_queue_buf() API for raw buffer queuing Sumit Kumar
@ 2026-06-10 5:52 ` Sumit Kumar
2 siblings, 0 replies; 4+ messages in thread
From: Sumit Kumar @ 2026-06-10 5:52 UTC (permalink / raw)
To: Manivannan Sadhasivam
Cc: mhi, linux-arm-msm, linux-kernel, Sumit Kumar, Krishna Chaitanya Chundru
When an MHI endpoint device runs Linux, there is no firmware to implement
the LOOPBACK channel echo that real modem firmware provides. Without an
endpoint-side driver, the host loopback test has no software echo partner
and cannot exercise the full end-to-end MHI data path.
Add an endpoint-side loopback driver that binds to the LOOPBACK channel and
echoes received data back to the host. An ordered workqueue is used for
asynchronous processing to preserve packet ordering. Together with the
host-side loopback driver, this enables complete MHI data path validation
for Linux-based endpoint devices.
Co-developed-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
Signed-off-by: Sumit Kumar <sumit.kumar@oss.qualcomm.com>
---
drivers/bus/mhi/ep/Kconfig | 2 +
drivers/bus/mhi/ep/Makefile | 1 +
drivers/bus/mhi/ep/clients/Kconfig | 16 +++++
drivers/bus/mhi/ep/clients/Makefile | 2 +
drivers/bus/mhi/ep/clients/loopback.c | 122 ++++++++++++++++++++++++++++++++++
5 files changed, 143 insertions(+)
diff --git a/drivers/bus/mhi/ep/Kconfig b/drivers/bus/mhi/ep/Kconfig
index 90ab3b040672e0f04181d4802e3062afcc7cf782..9edb81b39890e093a51138465a4d7705767eafa5 100644
--- a/drivers/bus/mhi/ep/Kconfig
+++ b/drivers/bus/mhi/ep/Kconfig
@@ -8,3 +8,5 @@ config MHI_BUS_EP
MHI_BUS_EP implements the MHI protocol for the endpoint devices,
such as SDX55 modem connected to the host machine over PCIe.
+
+source "drivers/bus/mhi/ep/clients/Kconfig"
diff --git a/drivers/bus/mhi/ep/Makefile b/drivers/bus/mhi/ep/Makefile
index aad85f180b707fb997fcb541837eda9bbbb67437..ab36ef2a40ab8174e5ddae44a3e6ccb8eb31168d 100644
--- a/drivers/bus/mhi/ep/Makefile
+++ b/drivers/bus/mhi/ep/Makefile
@@ -1,2 +1,3 @@
obj-$(CONFIG_MHI_BUS_EP) += mhi_ep.o
mhi_ep-y := main.o mmio.o ring.o sm.o
+obj-y += clients/
diff --git a/drivers/bus/mhi/ep/clients/Kconfig b/drivers/bus/mhi/ep/clients/Kconfig
new file mode 100644
index 0000000000000000000000000000000000000000..4cf27184058ca2be020885b6f57b4cc44b5054b6
--- /dev/null
+++ b/drivers/bus/mhi/ep/clients/Kconfig
@@ -0,0 +1,16 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config MHI_BUS_EP_LOOPBACK
+ tristate "MHI Endpoint LOOPBACK client driver"
+ depends on MHI_BUS_EP
+ help
+ MHI Endpoint LOOPBACK client driver that binds to the MHI LOOPBACK
+ channel as defined in the MHI specification. The LOOPBACK channel is
+ implemented by MHI-based endpoint devices (modems, WLAN) in the field,
+ where the endpoint firmware echoes back whatever the host sends.
+
+ This driver receives data on the uplink channel and echoes it back on
+ the downlink channel for testing the MHI endpoint data path.
+
+ To compile this driver as a module, choose M here. The module
+ will be called mhi_ep_loopback.
diff --git a/drivers/bus/mhi/ep/clients/Makefile b/drivers/bus/mhi/ep/clients/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..71dc91cc63b02592b177cf66db6090748c0653a6
--- /dev/null
+++ b/drivers/bus/mhi/ep/clients/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_MHI_BUS_EP_LOOPBACK) += mhi_ep_loopback.o
+mhi_ep_loopback-y += loopback.o
diff --git a/drivers/bus/mhi/ep/clients/loopback.c b/drivers/bus/mhi/ep/clients/loopback.c
new file mode 100644
index 0000000000000000000000000000000000000000..f346ad9ffca9eb957680b1d259c9789e55cffae9
--- /dev/null
+++ b/drivers/bus/mhi/ep/clients/loopback.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ */
+
+#include <linux/mhi_ep.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/string.h>
+
+struct mhi_ep_loopback {
+ struct workqueue_struct *loopback_wq;
+ struct mhi_ep_device *mdev;
+};
+
+struct mhi_ep_loopback_work {
+ struct mhi_ep_device *mdev;
+ struct work_struct work;
+ void *buf;
+ size_t len;
+};
+
+static void mhi_ep_loopback_work_handler(struct work_struct *work)
+{
+ struct mhi_ep_loopback_work *mhi_ep_lb_work = container_of(work,
+ struct mhi_ep_loopback_work, work);
+ int ret;
+
+ ret = mhi_ep_queue_buf(mhi_ep_lb_work->mdev, mhi_ep_lb_work->buf,
+ mhi_ep_lb_work->len);
+ if (ret) {
+ dev_err(&mhi_ep_lb_work->mdev->dev, "Failed to send the packet\n");
+ kfree(mhi_ep_lb_work->buf);
+ }
+
+ kfree(mhi_ep_lb_work);
+}
+
+static void mhi_ep_loopback_ul_callback(struct mhi_ep_device *mhi_dev,
+ struct mhi_result *mhi_res)
+{
+ struct mhi_ep_loopback *mhi_ep_lb = dev_get_drvdata(&mhi_dev->dev);
+ struct mhi_ep_loopback_work *mhi_ep_lb_work;
+ void *buf;
+
+ if (!mhi_res->transaction_status) {
+ buf = kmemdup(mhi_res->buf_addr, mhi_res->bytes_xferd, GFP_KERNEL);
+ if (!buf)
+ return;
+
+ mhi_ep_lb_work = kmalloc(sizeof(*mhi_ep_lb_work), GFP_KERNEL);
+ if (!mhi_ep_lb_work) {
+ kfree(buf);
+ return;
+ }
+
+ INIT_WORK(&mhi_ep_lb_work->work, mhi_ep_loopback_work_handler);
+ mhi_ep_lb_work->mdev = mhi_dev;
+ mhi_ep_lb_work->buf = buf;
+ mhi_ep_lb_work->len = mhi_res->bytes_xferd;
+
+ queue_work(mhi_ep_lb->loopback_wq, &mhi_ep_lb_work->work);
+ }
+}
+
+static void mhi_ep_loopback_dl_callback(struct mhi_ep_device *mhi_dev,
+ struct mhi_result *mhi_res)
+{
+ kfree(mhi_res->buf_addr);
+}
+
+static int mhi_ep_loopback_probe(struct mhi_ep_device *mhi_dev, const struct mhi_device_id *id)
+{
+ struct mhi_ep_loopback *mhi_ep_lb;
+
+ mhi_ep_lb = devm_kzalloc(&mhi_dev->dev, sizeof(*mhi_ep_lb), GFP_KERNEL);
+ if (!mhi_ep_lb)
+ return -ENOMEM;
+
+ mhi_ep_lb->loopback_wq = alloc_ordered_workqueue("mhi_ep_loopback", WQ_MEM_RECLAIM);
+ if (!mhi_ep_lb->loopback_wq) {
+ dev_err(&mhi_dev->dev, "Failed to create workqueue.\n");
+ return -ENOMEM;
+ }
+
+ mhi_ep_lb->mdev = mhi_dev;
+ dev_set_drvdata(&mhi_dev->dev, mhi_ep_lb);
+
+ return 0;
+}
+
+static void mhi_ep_loopback_remove(struct mhi_ep_device *mhi_dev)
+{
+ struct mhi_ep_loopback *mhi_ep_lb = dev_get_drvdata(&mhi_dev->dev);
+
+ destroy_workqueue(mhi_ep_lb->loopback_wq);
+ dev_set_drvdata(&mhi_dev->dev, NULL);
+}
+
+static const struct mhi_device_id mhi_ep_loopback_id_table[] = {
+ { .chan = "LOOPBACK"},
+ {}
+};
+MODULE_DEVICE_TABLE(mhi, mhi_ep_loopback_id_table);
+
+static struct mhi_ep_driver mhi_ep_loopback_driver = {
+ .probe = mhi_ep_loopback_probe,
+ .remove = mhi_ep_loopback_remove,
+ .dl_xfer_cb = mhi_ep_loopback_dl_callback,
+ .ul_xfer_cb = mhi_ep_loopback_ul_callback,
+ .id_table = mhi_ep_loopback_id_table,
+ .driver = {
+ .name = "mhi_ep_loopback",
+ },
+};
+
+module_mhi_ep_driver(mhi_ep_loopback_driver);
+
+MODULE_AUTHOR("Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>");
+MODULE_AUTHOR("Sumit Kumar <sumit.kumar@oss.qualcomm.com>");
+MODULE_DESCRIPTION("MHI Endpoint Loopback driver");
+MODULE_LICENSE("GPL");
--
2.34.1
^ permalink raw reply [flat|nested] 4+ messages in thread