Re: [PATCH v9 1/6] drm/panthor: Expose GPU page sizes to UM

["Adrián Larumbe" <adrian.larumbe@collabora.com>]

On 24.04.2026 14:18, Steven Price wrote:
> On 22/04/2026 13:25, Adrián Larumbe wrote:
> > In future commits that will implement repeated mappings, only repeat
> > values multiple of GPU page sizes will be tolerated. That means these
> > values must be made known to UM. Do it through a queriable GPU info
> > value.
> >
> > Reviewed-by: Steven Price <steven.price@arm.com>
> > Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_device.h |  3 +++
> >  drivers/gpu/drm/panthor/panthor_drv.c    |  8 ++++++++
> >  drivers/gpu/drm/panthor/panthor_mmu.c    |  9 ++++++++-
> >  include/uapi/drm/panthor_drm.h           | 13 +++++++++++++
> >  4 files changed, 32 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/gpu/drm/panthor/panthor_device.h
> > index 5cba272f9b4d..d856a4fe1d61 100644
> > --- a/drivers/gpu/drm/panthor/panthor_device.h
> > +++ b/drivers/gpu/drm/panthor/panthor_device.h
> > @@ -158,6 +158,9 @@ struct panthor_device {
> >  	/** @csif_info: Command stream interface information. */
> >  	struct drm_panthor_csif_info csif_info;
> >
> > +	/** @mmu_info: MMU info */
> > +	struct drm_panthor_mmu_info mmu_info;
> > +
> >  	/** @hw: GPU-specific data. */
> >  	struct panthor_hw *hw;
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_drv.c b/drivers/gpu/drm/panthor/panthor_drv.c
> > index 73fc983dc9b4..a8090bc4e33c 100644
> > --- a/drivers/gpu/drm/panthor/panthor_drv.c
> > +++ b/drivers/gpu/drm/panthor/panthor_drv.c
> > @@ -175,6 +175,7 @@ panthor_get_uobj_array(const struct drm_panthor_obj_array *in, u32 min_stride,
> >  	_Generic(_obj_name, \
> >  		 PANTHOR_UOBJ_DECL(struct drm_panthor_gpu_info, tiler_present), \
> >  		 PANTHOR_UOBJ_DECL(struct drm_panthor_csif_info, pad), \
> > +		 PANTHOR_UOBJ_DECL(struct drm_panthor_mmu_info, page_size_bitmap), \
> >  		 PANTHOR_UOBJ_DECL(struct drm_panthor_timestamp_info, current_timestamp), \
> >  		 PANTHOR_UOBJ_DECL(struct drm_panthor_group_priorities_info, pad), \
> >  		 PANTHOR_UOBJ_DECL(struct drm_panthor_sync_op, timeline_value), \
> > @@ -946,6 +947,10 @@ static int panthor_ioctl_dev_query(struct drm_device *ddev, void *data, struct d
> >  			args->size = sizeof(ptdev->csif_info);
> >  			return 0;
> >
> > +		case DRM_PANTHOR_DEV_QUERY_MMU_INFO:
> > +			args->size = sizeof(ptdev->mmu_info);
> > +			return 0;
> > +
> >  		case DRM_PANTHOR_DEV_QUERY_TIMESTAMP_INFO:
> >  			args->size = sizeof(timestamp_info);
> >  			return 0;
> > @@ -966,6 +971,9 @@ static int panthor_ioctl_dev_query(struct drm_device *ddev, void *data, struct d
> >  	case DRM_PANTHOR_DEV_QUERY_CSIF_INFO:
> >  		return PANTHOR_UOBJ_SET(args->pointer, args->size, ptdev->csif_info);
> >
> > +	case DRM_PANTHOR_DEV_QUERY_MMU_INFO:
> > +		return PANTHOR_UOBJ_SET(args->pointer, args->size, ptdev->mmu_info);
> > +
> >  	case DRM_PANTHOR_DEV_QUERY_TIMESTAMP_INFO:
> >  		ret = copy_struct_from_user(&timestamp_info,
> >  					    sizeof(timestamp_info),
> > diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c b/drivers/gpu/drm/panthor/panthor_mmu.c
> > index fa8b31df85c9..dad56a01c597 100644
> > --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> > +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> > @@ -2750,7 +2750,7 @@ panthor_vm_create(struct panthor_device *ptdev, bool for_mcu,
> >  	refcount_set(&vm->as.active_cnt, 0);
> >
> >  	pgtbl_cfg = (struct io_pgtable_cfg) {
> > -		.pgsize_bitmap	= SZ_4K | SZ_2M,
> > +		.pgsize_bitmap	= ptdev->mmu_info.page_size_bitmap,
> >  		.ias		= va_bits,
> >  		.oas		= pa_bits,
> >  		.coherent_walk	= ptdev->coherent,
> > @@ -3195,6 +3195,11 @@ static void panthor_mmu_release_wq(struct drm_device *ddev, void *res)
> >  	destroy_workqueue(res);
> >  }
> >
> > +static void panthor_mmu_info_init(struct panthor_device *ptdev)
> > +{
> > +	ptdev->mmu_info.page_size_bitmap = SZ_4K | SZ_2M;
> > +}
> > +
> >  /**
> >   * panthor_mmu_init() - Initialize the MMU logic.
> >   * @ptdev: Device.
> > @@ -3207,6 +3212,8 @@ int panthor_mmu_init(struct panthor_device *ptdev)
> >  	struct panthor_mmu *mmu;
> >  	int ret, irq;
> >
> > +	panthor_mmu_info_init(ptdev);
> > +
> >  	mmu = drmm_kzalloc(&ptdev->base, sizeof(*mmu), GFP_KERNEL);
> >  	if (!mmu)
> >  		return -ENOMEM;
> > diff --git a/include/uapi/drm/panthor_drm.h b/include/uapi/drm/panthor_drm.h
> > index 0e455d91e77d..dc2704fc2829 100644
> > --- a/include/uapi/drm/panthor_drm.h
> > +++ b/include/uapi/drm/panthor_drm.h
> > @@ -246,6 +246,9 @@ enum drm_panthor_dev_query_type {
> >  	/** @DRM_PANTHOR_DEV_QUERY_CSIF_INFO: Query command-stream interface information. */
> >  	DRM_PANTHOR_DEV_QUERY_CSIF_INFO,
> >
> > +	/** @DRM_PANTHOR_DEV_QUERY_MMU_INFO: Query MMU information. */
> > +	DRM_PANTHOR_DEV_QUERY_MMU_INFO,
> > +
>
> This is why I dislike enums... there's a comment above this:
>
> > /**
> >  * enum drm_panthor_dev_query_type - Query type
> >  *
> >  * Place new types at the end, don't re-order, don't remove or replace.
> >  */
>
> As it says - you need to place new types at the end, otherwise it
> changes the values for existing types (i.e. QUERY_TIMESTAMP_INFO below
> ends up with a new value).
>
> otherwise this will break old user space.

Thanks for catching this, it had completely escaped me.

> thanks,
> Steve
>
> >  	/** @DRM_PANTHOR_DEV_QUERY_TIMESTAMP_INFO: Query timestamp information. */
> >  	DRM_PANTHOR_DEV_QUERY_TIMESTAMP_INFO,
> >
> > @@ -487,6 +490,16 @@ struct drm_panthor_timestamp_info {
> >  	__u64 cpu_timestamp_nsec;
> >  };
> >
> > +/**
> > + * struct drm_panthor_mmu_info - MMU information
> > + *
> > + * Structure grouping all queryable information relating to the MMU.
> > + */
> > +struct drm_panthor_mmu_info {
> > +	/** @page_size_bitmap: Allowed page sizes */
> > +	__u64 page_size_bitmap;
> > +};
> > +
> >  /**
> >   * struct drm_panthor_group_priorities_info - Group priorities information
> >   *

Adrian Larumbe