[Linaro-mm-sig] Re: [PATCH RFC 05/18] accel/qda: Create compute CB devices on QDA compute bus

On 2/24/2026 4:19 AM, Dmitry Baryshkov wrote:

On Tue, Feb 24, 2026 at 12:38:59AM +0530, Ekansh Gupta wrote:

...

Add support for creating compute context-bank (CB) devices under the QDA compute bus based on child nodes of the FastRPC RPMsg device tree node. Each DT child with compatible "qcom,fastrpc-compute-cb" is turned into a QDA-owned struct device on qda_cb_bus_type.

A new qda_cb_dev structure and cb_devs list in qda_dev track these CB devices. qda_populate_child_devices() walks the DT children during QDA RPMsg probe, creates CB devices, configures their DMA and IOMMU settings using of_dma_configure(), and associates a SID from the "reg" property when present.

On RPMsg remove, qda_unpopulate_child_devices() tears down all CB devices, removing them from their IOMMU groups if present and unregistering the devices. This prepares the ground for using CB devices as IOMMU endpoints for DSP compute workloads in later patches.

Are we loosing the nsessions support?

Yes, it's not part of this series. I'll try bringing that as well.

...

Signed-off-by: Ekansh Gupta ekansh.gupta@oss.qualcomm.com

drivers/accel/qda/Makefile | 1 + drivers/accel/qda/qda_cb.c | 150 ++++++++++++++++++++++++++++++++++++++++++ drivers/accel/qda/qda_cb.h | 26 ++++++++ drivers/accel/qda/qda_drv.h | 3 + drivers/accel/qda/qda_rpmsg.c | 40 +++++++++++ 5 files changed, 220 insertions(+)

diff --git a/drivers/accel/qda/Makefile b/drivers/accel/qda/Makefile index 242684ef1af7..4aded20b6bc2 100644 --- a/drivers/accel/qda/Makefile +++ b/drivers/accel/qda/Makefile @@ -8,5 +8,6 @@ obj-$(CONFIG_DRM_ACCEL_QDA) := qda.o qda-y := \ qda_drv.o \ qda_rpmsg.o \

• qda_cb.o \

obj-$(CONFIG_DRM_ACCEL_QDA_COMPUTE_BUS) += qda_compute_bus.o diff --git a/drivers/accel/qda/qda_cb.c b/drivers/accel/qda/qda_cb.c new file mode 100644 index 000000000000..77a2d8cae076 --- /dev/null +++ b/drivers/accel/qda/qda_cb.c @@ -0,0 +1,150 @@ +// SPDX-License-Identifier: GPL-2.0-only +// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries. +#include <linux/dma-mapping.h> +#include <linux/device.h> +#include <linux/of.h> +#include <linux/of_device.h> +#include <linux/iommu.h> +#include <linux/slab.h> +#include "qda_drv.h" +#include "qda_cb.h"

+static void qda_cb_dev_release(struct device *dev) +{

• kfree(dev);

Do you need to put the reference on the OF node?

Reference put is happening as part of qda_destroy_cb_device.

...

+}

+static int qda_configure_cb_iommu(struct device *cb_dev, struct device_node *cb_node) +{

• int ret;
• qda_dbg(NULL, "Configuring DMA/IOMMU for CB device %s\n", dev_name(cb_dev));
• /* Use of_dma_configure which handles both DMA and IOMMU configuration */
• ret = of_dma_configure(cb_dev, cb_node, true);
• if (ret) {

• qda_err(NULL, "of_dma_configure failed for %s: %d\n", dev_name(cb_dev), ret);
  

• return ret;
  

• }
• qda_dbg(NULL, "DMA/IOMMU configured successfully for CB device %s\n", dev_name(cb_dev));
• return 0;

+}

+static int qda_cb_setup_device(struct qda_dev *qdev, struct device *cb_dev) +{

• int rc;
• u32 sid, pa_bits = 32;
• qda_dbg(qdev, "Setting up CB device %s\n", dev_name(cb_dev));
• if (of_property_read_u32(cb_dev->of_node, "reg", &sid)) {

• qda_dbg(qdev, "No 'reg' property found, defaulting SID to 0\n");
  

• sid = 0;
  

Don't do the job of the schema validator. Are there nodes without reg? No.

Ack.

...

• }
• rc = dma_set_mask(cb_dev, DMA_BIT_MASK(pa_bits));
• if (rc) {

• qda_err(qdev, "%d bit DMA enable failed: %d\n", pa_bits, rc);
  

• return rc;
  

• }
• qda_dbg(qdev, "CB device setup complete - SID: %u, PA bits: %u\n", sid, pa_bits);
• return 0;

+}

+int qda_create_cb_device(struct qda_dev *qdev, struct device_node *cb_node) +{

• struct device *cb_dev;
• int ret;
• u32 sid = 0;
• struct qda_cb_dev *entry;
• qda_dbg(qdev, "Creating CB device for node: %s\n", cb_node->name);
• of_property_read_u32(cb_node, "reg", &sid);
• cb_dev = kzalloc_obj(*cb_dev, GFP_KERNEL);
• if (!cb_dev)

• return -ENOMEM;
  

• device_initialize(cb_dev);
• cb_dev->parent = qdev->dev;
• cb_dev->bus = &qda_cb_bus_type; /* Use our custom bus type for IOMMU handling */
• cb_dev->release = qda_cb_dev_release;
• dev_set_name(cb_dev, "qda-cb-%s-%u", qdev->dsp_name, sid);
• qda_dbg(qdev, "Initialized CB device: %s\n", dev_name(cb_dev));
• cb_dev->of_node = of_node_get(cb_node);
• cb_dev->dma_mask = &cb_dev->coherent_dma_mask;
• cb_dev->coherent_dma_mask = DMA_BIT_MASK(32);
• dev_set_drvdata(cb_dev->parent, qdev);
• ret = device_add(cb_dev);
• if (ret) {

• qda_err(qdev, "Failed to add CB device for SID %u: %d\n", sid, ret);
  

• goto cleanup_device_init;
  

• }
• qda_dbg(qdev, "CB device added to system\n");
• ret = qda_configure_cb_iommu(cb_dev, cb_node);
• if (ret) {

• qda_err(qdev, "IOMMU configuration failed: %d\n", ret);
  

• goto cleanup_device_add;
  

• }
• ret = qda_cb_setup_device(qdev, cb_dev);
• if (ret) {

• qda_err(qdev, "CB device setup failed: %d\n", ret);
  

• goto cleanup_device_add;
  

• }
• entry = kzalloc(sizeof(*entry), GFP_KERNEL);
• if (!entry) {

• ret = -ENOMEM;
  

• goto cleanup_device_add;
  

• }
• entry->dev = cb_dev;
• list_add_tail(&entry->node, &qdev->cb_devs);
• qda_dbg(qdev, "Successfully created CB device for SID %u\n", sid);
• return 0;

+cleanup_device_add:

• device_del(cb_dev);

+cleanup_device_init:

• of_node_put(cb_dev->of_node);
• put_device(cb_dev);
• return ret;

+}

+void qda_destroy_cb_device(struct device *cb_dev) +{

• struct iommu_group *group;
• if (!cb_dev) {

• qda_dbg(NULL, "NULL CB device passed to destroy\n");
  

• return;
  

• }
• qda_dbg(NULL, "Destroying CB device %s\n", dev_name(cb_dev));
• group = iommu_group_get(cb_dev);
• if (group) {

• qda_dbg(NULL, "Removing %s from IOMMU group\n", dev_name(cb_dev));
  

• iommu_group_remove_device(cb_dev);
  

• iommu_group_put(group);
  

• }
• of_node_put(cb_dev->of_node);
• cb_dev->of_node = NULL;
• device_unregister(cb_dev);
• qda_dbg(NULL, "CB device %s destroyed\n", dev_name(cb_dev));

+} diff --git a/drivers/accel/qda/qda_cb.h b/drivers/accel/qda/qda_cb.h new file mode 100644 index 000000000000..a4ae9fef142e --- /dev/null +++ b/drivers/accel/qda/qda_cb.h @@ -0,0 +1,26 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/*

• • Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
• */

+#ifndef __QDA_CB_H__ +#define __QDA_CB_H__

+#include <linux/device.h> +#include <linux/of.h> +#include <linux/list.h> +#include <linux/qda_compute_bus.h> +#include "qda_drv.h"

+struct qda_cb_dev {

• struct list_head node;
• struct device *dev;

+};

+/*

• • Compute bus (CB) device management
• */

+int qda_create_cb_device(struct qda_dev *qdev, struct device_node *cb_node); +void qda_destroy_cb_device(struct device *cb_dev);

+#endif /* __QDA_CB_H__ */ diff --git a/drivers/accel/qda/qda_drv.h b/drivers/accel/qda/qda_drv.h index bec2d31ca1bb..eb732b7d8091 100644 --- a/drivers/accel/qda/qda_drv.h +++ b/drivers/accel/qda/qda_drv.h @@ -7,6 +7,7 @@ #define __QDA_DRV_H__ #include <linux/device.h> +#include <linux/list.h> #include <linux/mutex.h> #include <linux/rpmsg.h> #include <linux/xarray.h> @@ -26,6 +27,8 @@ struct qda_dev { atomic_t removing; /* Name of the DSP (e.g., "cdsp", "adsp") */ char dsp_name[16];

• /* Compute context-bank (CB) child devices */
• struct list_head cb_devs;

}; /** diff --git a/drivers/accel/qda/qda_rpmsg.c b/drivers/accel/qda/qda_rpmsg.c index a8b24a99ca13..5a57384de6a2 100644 --- a/drivers/accel/qda/qda_rpmsg.c +++ b/drivers/accel/qda/qda_rpmsg.c @@ -7,6 +7,7 @@ #include <linux/of_device.h> #include "qda_drv.h" #include "qda_rpmsg.h" +#include "qda_cb.h" static int qda_rpmsg_init(struct qda_dev *qdev) { @@ -25,11 +26,42 @@ static struct qda_dev *alloc_and_init_qdev(struct rpmsg_device *rpdev) qdev->dev = &rpdev->dev; qdev->rpdev = rpdev;

• INIT_LIST_HEAD(&qdev->cb_devs);

qda_dbg(qdev, "Allocated and initialized qda_dev\n"); return qdev; } +static void qda_unpopulate_child_devices(struct qda_dev *qdev) +{

• struct qda_cb_dev *entry, *tmp;
• list_for_each_entry_safe(entry, tmp, &qdev->cb_devs, node) {

• list_del(&entry->node);
  

• qda_destroy_cb_device(entry->dev);
  

• kfree(entry);
  

Why can't you embed struct device into a structure together with the list_node (and possibly some other data?)?

I'll check this.

...

• }

+}

+static int qda_populate_child_devices(struct qda_dev *qdev, struct device_node *parent_node) +{

• struct device_node *child;
• int count = 0, success = 0;
• for_each_child_of_node(parent_node, child) {

• if (of_device_is_compatible(child, "qcom,fastrpc-compute-cb")) {
  

• 	count++;
  

• 	if (qda_create_cb_device(qdev, child) == 0) {
  

• 		success++;
  

• 		qda_dbg(qdev, "Created CB device for node: %s\n", child->name);
  

• 	} else {
  

• 		qda_err(qdev, "Failed to create CB device for: %s\n", child->name);
  

Don't loose the error code. Instead please return it to the caller.

Ack.

...

• 	}
  

• }
  

• }
• return success > 0 ? 0 : (count > 0 ? -ENODEV : 0);

+}

static int qda_rpmsg_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src) { /* Dummy function for rpmsg driver */ @@ -48,6 +80,7 @@ static void qda_rpmsg_remove(struct rpmsg_device *rpdev) qdev->rpdev = NULL; mutex_unlock(&qdev->lock);

• qda_unpopulate_child_devices(qdev); qda_deinit_device(qdev);

qda_info(qdev, "RPMsg device removed\n"); @@ -83,6 +116,13 @@ static int qda_rpmsg_probe(struct rpmsg_device *rpdev) if (ret) return ret;

• ret = qda_populate_child_devices(qdev, rpdev->dev.of_node);
• if (ret) {

• qda_err(qdev, "Failed to populate child devices: %d\n", ret);
  

• qda_deinit_device(qdev);
  

• return ret;
  

• }
• qda_info(qdev, "QDA RPMsg probe completed successfully for %s\n", qdev->dsp_name); return 0;

}

-- 2.34.1