Re: [PATCH RFC 08/18] accel/qda: Add per-file DRM context and open/close handling

[Dmitry Baryshkov]

On Tue, Feb 24, 2026 at 12:39:02AM +0530, Ekansh Gupta wrote:
> Introduce per-file and per-user context for the QDA DRM accelerator
> driver. A new qda_file_priv structure is stored in file->driver_priv
> for each open file descriptor, and a qda_user object is allocated per
> client with a unique client_id generated from an atomic counter in
> qda_dev.
> 
> The DRM driver now provides qda_open() and qda_postclose() callbacks.
> qda_open() resolves the qda_dev from the drm_device, allocates the
> qda_file_priv and qda_user structures, and attaches them to the DRM
> file. qda_postclose() tears down the per-file context and frees the
> qda_user object when the file is closed.
> 
> This prepares the QDA driver to track per-process state for future
> features such as per-client memory mappings, job submission contexts,
> and access control over DSP compute resources.

Start by describing the problem instead of stuffing it to the end. Can
we use something better suited for this task, like IDR?

> Signed-off-by: Ekansh Gupta <ekansh.gupta@xxxxxxxxxxxxxxxx>
> ---
>  drivers/accel/qda/qda_drv.c | 117 ++++++++++++++++++++++++++++++++++++++++++++
>  drivers/accel/qda/qda_drv.h |  30 ++++++++++++
>  2 files changed, 147 insertions(+)
> 
> diff --git a/drivers/accel/qda/qda_drv.c b/drivers/accel/qda/qda_drv.c
> index a9113ec78fa2..bf95fc782cf8 100644
> --- a/drivers/accel/qda/qda_drv.c
> +++ b/drivers/accel/qda/qda_drv.c
> @@ -12,11 +12,127 @@
>  #include "qda_drv.h"
>  #include "qda_rpmsg.h"
>  
> +static struct qda_drm_priv *get_drm_priv_from_device(struct drm_device *dev)
> +{
> +	if (!dev)
> +		return NULL;
> +
> +	return (struct qda_drm_priv *)dev->dev_private;
> +}
> +
> +static struct qda_dev *get_qdev_from_drm_device(struct drm_device *dev)
> +{
> +	struct qda_drm_priv *drm_priv;
> +
> +	if (!dev) {
> +		qda_dbg(NULL, "Invalid drm_device\n");
> +		return NULL;
> +	}
> +
> +	drm_priv = get_drm_priv_from_device(dev);
> +	if (!drm_priv) {
> +		qda_dbg(NULL, "No drm_priv in dev_private\n");
> +		return NULL;
> +	}
> +
> +	return drm_priv->qdev;
> +}
> +
> +static struct qda_user *alloc_qda_user(struct qda_dev *qdev)
> +{
> +	struct qda_user *qda_user;
> +
> +	qda_user = kzalloc_obj(*qda_user, GFP_KERNEL);
> +	if (!qda_user)
> +		return NULL;
> +
> +	qda_user->client_id = atomic_inc_return(&qdev->client_id_counter);
> +	qda_user->qda_dev = qdev;
> +
> +	qda_dbg(qdev, "Allocated qda_user with client_id=%u\n", qda_user->client_id);
> +	return qda_user;
> +}
> +
> +static void free_qda_user(struct qda_user *qda_user)
> +{
> +	if (!qda_user)
> +		return;
> +
> +	qda_dbg(qda_user->qda_dev, "Freeing qda_user client_id=%u\n", qda_user->client_id);
> +
> +	kfree(qda_user);
> +}
> +
> +static int qda_open(struct drm_device *dev, struct drm_file *file)
> +{
> +	struct qda_user *qda_user;
> +	struct qda_file_priv *qda_file_priv;
> +	struct qda_dev *qdev;
> +
> +	if (!file) {
> +		qda_dbg(NULL, "Invalid file pointer\n");
> +		return -EINVAL;
> +	}
> +
> +	qdev = get_qdev_from_drm_device(dev);
> +	if (!qdev) {
> +		qda_dbg(NULL, "Failed to get qdev from drm_device\n");
> +		return -EINVAL;
> +	}
> +
> +	qda_file_priv = kzalloc(sizeof(*qda_file_priv), GFP_KERNEL);
> +	if (!qda_file_priv)
> +		return -ENOMEM;
> +
> +	qda_file_priv->pid = current->pid;
> +
> +	qda_user = alloc_qda_user(qdev);
> +	if (!qda_user) {
> +		qda_dbg(qdev, "Failed to allocate qda_user\n");
> +		kfree(qda_file_priv);
> +		return -ENOMEM;
> +	}
> +
> +	file->driver_priv = qda_file_priv;
> +	qda_file_priv->qda_user = qda_user;
> +
> +	qda_dbg(qdev, "Device opened successfully for PID %d\n", current->pid);
> +
> +	return 0;
> +}
> +
> +static void qda_postclose(struct drm_device *dev, struct drm_file *file)
> +{
> +	struct qda_dev *qdev;
> +	struct qda_file_priv *qda_file_priv;
> +	struct qda_user *qda_user;
> +
> +	qdev = get_qdev_from_drm_device(dev);
> +	if (!qdev || atomic_read(&qdev->removing)) {
> +		qda_dbg(NULL, "Device unavailable or removing\n");
> +		return;

Even if it is being removed, no need to free the memory?

> +	}
> +
> +	qda_file_priv = (struct qda_file_priv *)file->driver_priv;
> +	if (qda_file_priv) {
> +		qda_user = qda_file_priv->qda_user;
> +		if (qda_user)
> +			free_qda_user(qda_user);
> +
> +		kfree(qda_file_priv);
> +		file->driver_priv = NULL;
> +	}
> +
> +	qda_dbg(qdev, "Device closed for PID %d\n", current->pid);
> +}
> +
>  DEFINE_DRM_ACCEL_FOPS(qda_accel_fops);
>  
>  static struct drm_driver qda_drm_driver = {
>  	.driver_features = DRIVER_COMPUTE_ACCEL,
>  	.fops			= &qda_accel_fops,
> +	.open			= qda_open,
> +	.postclose		= qda_postclose,
>  	.name = DRIVER_NAME,
>  	.desc = "Qualcomm DSP Accelerator Driver",
>  };
> @@ -58,6 +174,7 @@ static void init_device_resources(struct qda_dev *qdev)
>  
>  	mutex_init(&qdev->lock);
>  	atomic_set(&qdev->removing, 0);
> +	atomic_set(&qdev->client_id_counter, 0);
>  }
>  
>  static int init_memory_manager(struct qda_dev *qdev)
> diff --git a/drivers/accel/qda/qda_drv.h b/drivers/accel/qda/qda_drv.h
> index 2b80401a3741..e0ba37702a86 100644
> --- a/drivers/accel/qda/qda_drv.h
> +++ b/drivers/accel/qda/qda_drv.h
> @@ -10,6 +10,7 @@
>  #include <linux/list.h>
>  #include <linux/mutex.h>
>  #include <linux/rpmsg.h>
> +#include <linux/types.h>
>  #include <linux/xarray.h>
>  #include <drm/drm_drv.h>
>  #include <drm/drm_file.h>
> @@ -20,6 +21,33 @@
>  /* Driver identification */
>  #define DRIVER_NAME "qda"
>  
> +/**
> + * struct qda_file_priv - Per-process private data for DRM file
> + *
> + * This structure tracks per-process state for each open file descriptor.
> + * It maintains the IOMMU device assignment and links to the legacy qda_user
> + * structure for compatibility with existing code.
> + */
> +struct qda_file_priv {
> +	/* Process ID for tracking */
> +	pid_t pid;
> +	/* Pointer to qda_user structure for backward compatibility */
> +	struct qda_user *qda_user;
> +};
> +
> +/**
> + * struct qda_user - Per-user context for remote processor interaction
> + *
> + * This structure maintains per-user state for interactions with the
> + * remote processor, including memory mappings and pending operations.
> + */
> +struct qda_user {
> +	/* Unique client identifier */
> +	u32 client_id;
> +	/* Back-pointer to device structure */
> +	struct qda_dev *qda_dev;
> +};
> +
>  /**
>   * struct qda_drm_priv - DRM device private data for QDA device
>   *
> @@ -52,6 +80,8 @@ struct qda_dev {
>  	struct qda_drm_priv *drm_priv;
>  	/* Flag indicating device removal in progress */
>  	atomic_t removing;
> +	/* Atomic counter for generating unique client IDs */
> +	atomic_t client_id_counter;
>  	/* Name of the DSP (e.g., "cdsp", "adsp") */
>  	char dsp_name[16];
>  	/* Compute context-bank (CB) child devices */
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry