Re: [PATCH RFC 11/18] accel/qda: Add GEM_CREATE and GEM_MMAP_OFFSET IOCTLs

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Tue, Feb 24, 2026 at 12:39:05AM +0530, Ekansh Gupta wrote:
> Add two GEM-related IOCTLs for the QDA accelerator driver and hook
> them into the DRM accel driver. DRM_IOCTL_QDA_GEM_CREATE allocates
> a DMA-backed GEM buffer object via qda_gem_create_object() and
> returns a GEM handle to userspace, while
> DRM_IOCTL_QDA_GEM_MMAP_OFFSET returns a valid mmap offset for a
> given GEM handle using drm_gem_create_mmap_offset() and the
> vma_node in the GEM object.
> 
> The QDA driver is updated to advertise DRIVER_GEM in its
> driver_features, and the new IOCTLs are wired through the QDA
> GEM and memory-manager backend. These IOCTLs allow userspace to
> allocate buffers and map them into its address space as a first
> step toward full compute buffer management and integration with
> DSP workloads.
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
> ---
>  drivers/accel/qda/qda_drv.c   |  5 ++++-
>  drivers/accel/qda/qda_gem.h   | 30 ++++++++++++++++++++++++++++++
>  drivers/accel/qda/qda_ioctl.c | 35 +++++++++++++++++++++++++++++++++++
>  include/uapi/drm/qda_accel.h  | 36 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 105 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/accel/qda/qda_drv.c b/drivers/accel/qda/qda_drv.c
> index 19798359b14e..0dd0e2bb2c0f 100644
> --- a/drivers/accel/qda/qda_drv.c
> +++ b/drivers/accel/qda/qda_drv.c
> @@ -12,6 +12,7 @@
>  #include <drm/qda_accel.h>
>  
>  #include "qda_drv.h"
> +#include "qda_gem.h"
>  #include "qda_ioctl.h"
>  #include "qda_rpmsg.h"
>  
> @@ -154,10 +155,12 @@ DEFINE_DRM_ACCEL_FOPS(qda_accel_fops);
>  
>  static const struct drm_ioctl_desc qda_ioctls[] = {
>  	DRM_IOCTL_DEF_DRV(QDA_QUERY, qda_ioctl_query, 0),
> +	DRM_IOCTL_DEF_DRV(QDA_GEM_CREATE, qda_ioctl_gem_create, 0),
> +	DRM_IOCTL_DEF_DRV(QDA_GEM_MMAP_OFFSET, qda_ioctl_gem_mmap_offset, 0),
>  };
>  
>  static struct drm_driver qda_drm_driver = {
> -	.driver_features = DRIVER_COMPUTE_ACCEL,
> +	.driver_features = DRIVER_GEM | DRIVER_COMPUTE_ACCEL,
>  	.fops			= &qda_accel_fops,
>  	.open			= qda_open,
>  	.postclose		= qda_postclose,
> diff --git a/drivers/accel/qda/qda_gem.h b/drivers/accel/qda/qda_gem.h
> index caae9cda5363..cbd5d0a58fa4 100644
> --- a/drivers/accel/qda/qda_gem.h
> +++ b/drivers/accel/qda/qda_gem.h
> @@ -47,6 +47,36 @@ struct drm_gem_object *qda_gem_create_object(struct drm_device *drm_dev,
>  void qda_gem_free_object(struct drm_gem_object *gem_obj);
>  int qda_gem_mmap_obj(struct drm_gem_object *gem_obj, struct vm_area_struct *vma);
>  
> +/*
> + * GEM IOCTL handlers
> + */
> +
> +/**
> + * qda_ioctl_gem_create - Create a GEM buffer object
> + * @dev: DRM device structure
> + * @data: User-space data containing buffer creation parameters
> + * @file_priv: DRM file private data
> + *
> + * This IOCTL handler creates a new GEM buffer object with the specified
> + * size and returns a handle to the created buffer.
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +int qda_ioctl_gem_create(struct drm_device *dev, void *data, struct drm_file *file_priv);
> +
> +/**
> + * qda_ioctl_gem_mmap_offset - Get mmap offset for a GEM buffer object
> + * @dev: DRM device structure
> + * @data: User-space data containing buffer handle and offset result
> + * @file_priv: DRM file private data
> + *
> + * This IOCTL handler retrieves the mmap offset for a GEM buffer object,
> + * which can be used to map the buffer into user-space memory.
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +int qda_ioctl_gem_mmap_offset(struct drm_device *dev, void *data, struct drm_file *file_priv);
> +
>  /*
>   * Helper functions for GEM object allocation and cleanup
>   * These are used internally and by the PRIME import code
> diff --git a/drivers/accel/qda/qda_ioctl.c b/drivers/accel/qda/qda_ioctl.c
> index 9fa73ec2dfce..ef3c9c691cb7 100644
> --- a/drivers/accel/qda/qda_ioctl.c
> +++ b/drivers/accel/qda/qda_ioctl.c
> @@ -43,3 +43,38 @@ int qda_ioctl_query(struct drm_device *dev, void *data, struct drm_file *file_pr
>  
>  	return 0;
>  }
> +
> +int qda_ioctl_gem_create(struct drm_device *dev, void *data, struct drm_file *file_priv)
> +{
> +	struct drm_qda_gem_create *args = data;
> +	struct drm_gem_object *gem_obj;
> +	struct qda_drm_priv *drm_priv;
> +
> +	drm_priv = get_drm_priv_from_device(dev);
> +	if (!drm_priv || !drm_priv->iommu_mgr)
> +		return -EINVAL;
> +
> +	gem_obj = qda_gem_create_object(dev, drm_priv->iommu_mgr, args->size, file_priv);
> +	if (IS_ERR(gem_obj))
> +		return PTR_ERR(gem_obj);
> +
> +	return qda_gem_create_handle(file_priv, gem_obj, &args->handle);
> +}
> +
> +int qda_ioctl_gem_mmap_offset(struct drm_device *dev, void *data, struct drm_file *file_priv)
> +{
> +	struct drm_qda_gem_mmap_offset *args = data;
> +	struct drm_gem_object *gem_obj;
> +	int ret;
> +
> +	gem_obj = qda_gem_lookup_object(file_priv, args->handle);
> +	if (IS_ERR(gem_obj))
> +		return PTR_ERR(gem_obj);
> +
> +	ret = drm_gem_create_mmap_offset(gem_obj);
> +	if (ret == 0)
> +		args->offset = drm_vma_node_offset_addr(&gem_obj->vma_node);
> +
> +	drm_gem_object_put(gem_obj);
> +	return ret;
> +}
> diff --git a/include/uapi/drm/qda_accel.h b/include/uapi/drm/qda_accel.h
> index 0aad791c4832..ed24a7f5637e 100644
> --- a/include/uapi/drm/qda_accel.h
> +++ b/include/uapi/drm/qda_accel.h
> @@ -19,6 +19,8 @@ extern "C" {
>   * They are used with DRM_COMMAND_BASE to create the full IOCTL numbers.
>   */
>  #define DRM_QDA_QUERY	0x00
> +#define DRM_QDA_GEM_CREATE		0x01
> +#define DRM_QDA_GEM_MMAP_OFFSET	0x02
>  /*
>   * QDA IOCTL definitions
>   *
> @@ -27,6 +29,10 @@ extern "C" {
>   * data structure and direction (read/write) for each IOCTL.
>   */
>  #define DRM_IOCTL_QDA_QUERY	DRM_IOR(DRM_COMMAND_BASE + DRM_QDA_QUERY, struct drm_qda_query)
> +#define DRM_IOCTL_QDA_GEM_CREATE	DRM_IOWR(DRM_COMMAND_BASE + DRM_QDA_GEM_CREATE, \
> +						 struct drm_qda_gem_create)
> +#define DRM_IOCTL_QDA_GEM_MMAP_OFFSET	DRM_IOWR(DRM_COMMAND_BASE + DRM_QDA_GEM_MMAP_OFFSET, \
> +						 struct drm_qda_gem_mmap_offset)
>  
>  /**
>   * struct drm_qda_query - Device information query structure
> @@ -40,6 +46,36 @@ struct drm_qda_query {
>  	__u8 dsp_name[16];
>  };
>  
> +/**
> + * struct drm_qda_gem_create - GEM buffer object creation parameters
> + * @size: Size of the GEM object to create in bytes (input)
> + * @handle: Allocated GEM handle (output)
> + *
> + * This structure is used with DRM_IOCTL_QDA_GEM_CREATE to allocate
> + * a new GEM buffer object.
> + */
> +struct drm_qda_gem_create {
> +	__u32 handle;
> +	__u32 pad;
> +	__u64 size;

If you put size before handle, you would not need padding.

> +};
> +
> +/**
> + * struct drm_qda_gem_mmap_offset - GEM object mmap offset query
> + * @handle: GEM handle (input)
> + * @pad: Padding for 64-bit alignment
> + * @offset: mmap offset for the GEM object (output)
> + *
> + * This structure is used with DRM_IOCTL_QDA_GEM_MMAP_OFFSET to retrieve
> + * the mmap offset that can be used with mmap() to map the GEM object into
> + * user space.
> + */
> +struct drm_qda_gem_mmap_offset {
> +	__u32 handle;
> +	__u32 pad;
> +	__u64 offset;

I'm really not a fan of the pad field in the middle of the structure.

> +};
> +
>  #if defined(__cplusplus)
>  }
>  #endif
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry