Re: [PATCH RFC 03/18] accel/qda: Add RPMsg transport for Qualcomm DSP accelerator

[Dmitry Baryshkov]

On Tue, Feb 24, 2026 at 12:38:57AM +0530, Ekansh Gupta wrote:
> Extend the Qualcomm DSP accelerator (QDA) driver with an RPMsg-based
> transport used to discover and manage DSP instances.
> 
> This patch introduces:
> 
> - A core qda_dev structure with basic device state (rpmsg device,
>   device pointer, lock, removal flag, DSP name).
> - Logging helpers that integrate with dev_* when a device is available
>   and fall back to pr_* otherwise.
> - An RPMsg client driver that binds to the Qualcomm FastRPC service and
>   allocates a qda_dev instance using devm_kzalloc().
> - Basic device initialization and teardown paths wired into the module
>   init/exit.
> 
> The RPMsg driver currently sets the DSP name from a "label" property in
> the device tree, which will be used by subsequent patches to distinguish
> between different DSP domains (e.g. ADSP, CDSP).
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@xxxxxxxxxxxxxxxx>
> ---
>  drivers/accel/qda/Kconfig     |   1 +
>  drivers/accel/qda/Makefile    |   4 +-
>  drivers/accel/qda/qda_drv.c   |  41 ++++++++++++++-
>  drivers/accel/qda/qda_drv.h   |  91 ++++++++++++++++++++++++++++++++
>  drivers/accel/qda/qda_rpmsg.c | 119 ++++++++++++++++++++++++++++++++++++++++++
>  drivers/accel/qda/qda_rpmsg.h |  17 ++++++
>  6 files changed, 270 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/accel/qda/Kconfig b/drivers/accel/qda/Kconfig
> index 3c78ff6189e0..484d21ff1b55 100644
> --- a/drivers/accel/qda/Kconfig
> +++ b/drivers/accel/qda/Kconfig
> @@ -7,6 +7,7 @@ config DRM_ACCEL_QDA
>  	tristate "Qualcomm DSP accelerator"
>  	depends on DRM_ACCEL
>  	depends on ARCH_QCOM || COMPILE_TEST
> +	depends on RPMSG
>  	help
>  	  Enables the DRM-based accelerator driver for Qualcomm's Hexagon DSPs.
>  	  This driver provides a standardized interface for offloading computational
> diff --git a/drivers/accel/qda/Makefile b/drivers/accel/qda/Makefile
> index 573711af1d28..e7f23182589b 100644
> --- a/drivers/accel/qda/Makefile
> +++ b/drivers/accel/qda/Makefile
> @@ -5,4 +5,6 @@
>  
>  obj-$(CONFIG_DRM_ACCEL_QDA)	:= qda.o
>  
> -qda-y := qda_drv.o
> +qda-y := \
> +	qda_drv.o \

Squash these parts into the previous patch.

> +	qda_rpmsg.o \
> diff --git a/drivers/accel/qda/qda_drv.c b/drivers/accel/qda/qda_drv.c
> index 18b0d3fb1598..389c66a9ad4f 100644
> --- a/drivers/accel/qda/qda_drv.c
> +++ b/drivers/accel/qda/qda_drv.c
> @@ -2,16 +2,53 @@
>  // Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
>  #include <linux/module.h>
>  #include <linux/kernel.h>
> +#include <linux/atomic.h>
> +#include "qda_drv.h"
> +#include "qda_rpmsg.h"
> +
> +static void cleanup_device_resources(struct qda_dev *qdev)
> +{
> +	mutex_destroy(&qdev->lock);
> +}
> +
> +void qda_deinit_device(struct qda_dev *qdev)
> +{
> +	cleanup_device_resources(qdev);
> +}
> +
> +/* Initialize device resources */
> +static void init_device_resources(struct qda_dev *qdev)
> +{
> +	qda_dbg(qdev, "Initializing device resources\n");
> +
> +	mutex_init(&qdev->lock);
> +	atomic_set(&qdev->removing, 0);
> +}
> +
> +int qda_init_device(struct qda_dev *qdev)
> +{
> +	init_device_resources(qdev);
> +
> +	qda_dbg(qdev, "QDA device initialized successfully\n");
> +	return 0;
> +}
>  
>  static int __init qda_core_init(void)
>  {
> -	pr_info("QDA: driver initialization complete\n");
> +	int ret;
> +
> +	ret = qda_rpmsg_register();
> +	if (ret)
> +		return ret;
> +
> +	qda_info(NULL, "QDA driver initialization complete\n");
>  	return 0;
>  }
>  
>  static void __exit qda_core_exit(void)
>  {
> -	pr_info("QDA: driver exit complete\n");
> +	qda_rpmsg_unregister();
> +	qda_info(NULL, "QDA driver exit complete\n");
>  }
>  
>  module_init(qda_core_init);
> diff --git a/drivers/accel/qda/qda_drv.h b/drivers/accel/qda/qda_drv.h
> new file mode 100644
> index 000000000000..bec2d31ca1bb
> --- /dev/null
> +++ b/drivers/accel/qda/qda_drv.h
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + */
> +
> +#ifndef __QDA_DRV_H__
> +#define __QDA_DRV_H__
> +
> +#include <linux/device.h>
> +#include <linux/mutex.h>
> +#include <linux/rpmsg.h>
> +#include <linux/xarray.h>
> +
> +/* Driver identification */
> +#define DRIVER_NAME "qda"
> +
> +/* struct qda_dev - Main device structure for QDA driver */
> +struct qda_dev {
> +	/* RPMsg device for communication with remote processor */
> +	struct rpmsg_device *rpdev;
> +	/* Underlying device structure */
> +	struct device *dev;
> +	/* Mutex protecting device state */
> +	struct mutex lock;

Which parts of the state?

> +	/* Flag indicating device removal in progress */
> +	atomic_t removing;

Why do you need it if we have dev->unplugged and drm_dev_enter() /
drm_dev_exit()?

> +	/* Name of the DSP (e.g., "cdsp", "adsp") */
> +	char dsp_name[16];

Please replace with the pointers to the static array.

> +};
> +
> +/**
> + * qda_get_log_device - Get appropriate device for logging
> + * @qdev: QDA device structure
> + *
> + * Returns the most appropriate device structure for logging messages.
> + * Prefers qdev->dev, or returns NULL if the device is being removed
> + * or invalid.
> + */
> +static inline struct device *qda_get_log_device(struct qda_dev *qdev)
> +{
> +	if (!qdev || atomic_read(&qdev->removing))
> +		return NULL;
> +
> +	if (qdev->dev)
> +		return qdev->dev;
> +
> +	return NULL;
> +}
> +
> +/*
> + * Logging macros
> + *
> + * These macros provide consistent logging across the driver with automatic
> + * function name inclusion. They use dev_* functions when a device is available,
> + * falling back to pr_* functions otherwise.
> + */
> +
> +/* Error logging - always logs and tracks errors */
> +#define qda_err(qdev, fmt, ...) do { \
> +	struct device *__dev = qda_get_log_device(qdev); \
> +	if (__dev) \
> +		dev_err(__dev, "[%s] " fmt, __func__, ##__VA_ARGS__); \
> +	else \
> +		pr_err(DRIVER_NAME ": [%s] " fmt, __func__, ##__VA_ARGS__); \

What /why? You are under drm, so you can use drm_* helpers instead.

> +} while (0)
> +
> +/* Info logging - always logs, can be filtered via loglevel */
> +#define qda_info(qdev, fmt, ...) do { \
> +	struct device *__dev = qda_get_log_device(qdev); \
> +	if (__dev) \
> +		dev_info(__dev, "[%s] " fmt, __func__, ##__VA_ARGS__); \
> +	else \
> +		pr_info(DRIVER_NAME ": [%s] " fmt, __func__, ##__VA_ARGS__); \
> +} while (0)
> +
> +/* Debug logging - controlled via dynamic debug (CONFIG_DYNAMIC_DEBUG) */
> +#define qda_dbg(qdev, fmt, ...) do { \
> +	struct device *__dev = qda_get_log_device(qdev); \
> +	if (__dev) \
> +		dev_dbg(__dev, "[%s] " fmt, __func__, ##__VA_ARGS__); \
> +	else \
> +		pr_debug(DRIVER_NAME ": [%s] " fmt, __func__, ##__VA_ARGS__); \
> +} while (0)
> +
> +/*
> + * Core device management functions
> + */
> +int qda_init_device(struct qda_dev *qdev);
> +void qda_deinit_device(struct qda_dev *qdev);
> +
> +#endif /* __QDA_DRV_H__ */
> diff --git a/drivers/accel/qda/qda_rpmsg.c b/drivers/accel/qda/qda_rpmsg.c
> new file mode 100644
> index 000000000000..a8b24a99ca13
> --- /dev/null
> +++ b/drivers/accel/qda/qda_rpmsg.c
> @@ -0,0 +1,119 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +// Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> +#include <linux/module.h>
> +#include <linux/rpmsg.h>
> +#include <linux/of_platform.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include "qda_drv.h"
> +#include "qda_rpmsg.h"
> +
> +static int qda_rpmsg_init(struct qda_dev *qdev)
> +{
> +	dev_set_drvdata(&qdev->rpdev->dev, qdev);
> +	return 0;
> +}
> +
> +/* Utility function to allocate and initialize qda_dev */
> +static struct qda_dev *alloc_and_init_qdev(struct rpmsg_device *rpdev)
> +{
> +	struct qda_dev *qdev;
> +
> +	qdev = devm_kzalloc(&rpdev->dev, sizeof(*qdev), GFP_KERNEL);
> +	if (!qdev)
> +		return ERR_PTR(-ENOMEM);
> +
> +	qdev->dev = &rpdev->dev;
> +	qdev->rpdev = rpdev;
> +
> +	qda_dbg(qdev, "Allocated and initialized qda_dev\n");
> +	return qdev;
> +}
> +
> +static int qda_rpmsg_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src)
> +{
> +	/* Dummy function for rpmsg driver */
> +	return 0;
> +}
> +
> +static void qda_rpmsg_remove(struct rpmsg_device *rpdev)
> +{
> +	struct qda_dev *qdev = dev_get_drvdata(&rpdev->dev);
> +
> +	qda_info(qdev, "Removing RPMsg device\n");
> +
> +	atomic_set(&qdev->removing, 1);
> +
> +	mutex_lock(&qdev->lock);
> +	qdev->rpdev = NULL;
> +	mutex_unlock(&qdev->lock);
> +
> +	qda_deinit_device(qdev);
> +
> +	qda_info(qdev, "RPMsg device removed\n");
> +}
> +
> +static int qda_rpmsg_probe(struct rpmsg_device *rpdev)
> +{
> +	struct qda_dev *qdev;
> +	int ret;
> +	const char *label;
> +
> +	qda_dbg(NULL, "QDA RPMsg probe starting\n");
> +
> +	qdev = alloc_and_init_qdev(rpdev);
> +	if (IS_ERR(qdev))
> +		return PTR_ERR(qdev);
> +
> +	ret = of_property_read_string(rpdev->dev.of_node, "label", &label);
> +	if (!ret) {
> +		strscpy(qdev->dsp_name, label, sizeof(qdev->dsp_name));
> +	} else {
> +		qda_info(qdev, "QDA DSP label not found in DT\n");
> +		return ret;
> +	}
> +
> +	ret = qda_rpmsg_init(qdev);
> +	if (ret) {
> +		qda_err(qdev, "RPMsg init failed: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = qda_init_device(qdev);
> +	if (ret)
> +		return ret;
> +
> +	qda_info(qdev, "QDA RPMsg probe completed successfully for %s\n", qdev->dsp_name);
> +	return 0;
> +}
> +
> +static const struct of_device_id qda_rpmsg_id_table[] = {
> +	{ .compatible = "qcom,fastrpc" },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, qda_rpmsg_id_table);
> +
> +static struct rpmsg_driver qda_rpmsg_driver = {
> +	.probe = qda_rpmsg_probe,
> +	.remove = qda_rpmsg_remove,
> +	.callback = qda_rpmsg_cb,
> +	.drv = {
> +		.name = "qcom,fastrpc",
> +		.of_match_table = qda_rpmsg_id_table,
> +	},
> +};
> +
> +int qda_rpmsg_register(void)
> +{
> +	int ret = register_rpmsg_driver(&qda_rpmsg_driver);
> +
> +	if (ret)
> +		qda_err(NULL, "Failed to register RPMsg driver: %d\n", ret);
> +
> +	return ret;
> +}
> +
> +void qda_rpmsg_unregister(void)
> +{
> +	unregister_rpmsg_driver(&qda_rpmsg_driver);
> +}
> diff --git a/drivers/accel/qda/qda_rpmsg.h b/drivers/accel/qda/qda_rpmsg.h
> new file mode 100644
> index 000000000000..348827bff255
> --- /dev/null
> +++ b/drivers/accel/qda/qda_rpmsg.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + */
> +
> +#ifndef __QDA_RPMSG_H__
> +#define __QDA_RPMSG_H__
> +
> +#include "qda_drv.h"
> +
> +/*
> + * Transport layer registration
> + */
> +int qda_rpmsg_register(void);
> +void qda_rpmsg_unregister(void);
> +
> +#endif /* __QDA_RPMSG_H__ */
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry