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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 Signed-off-by: Krishna Chaitanya Chundru Signed-off-by: Sumit Kumar --- .../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_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_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_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_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_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 +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#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 "); +MODULE_AUTHOR("Sumit Kumar "); +MODULE_DESCRIPTION("MHI Host Loopback Driver"); +MODULE_LICENSE("GPL"); -- 2.34.1