Re: [PATCH v4 2/3] drm: Add and export function drm_gem_cma_sync_data

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 15.05.21 um 16:53 schrieb Paul Cercueil:
> This function can be used by drivers that use damage clips and have
> CMA GEM objects backed by non-coherent memory. Calling this function
> in a plane's .atomic_update ensures that all the data in the backing
> memory have been written to RAM.
> 
> v3: - Only sync data if using GEM objects backed by non-coherent memory.
>      - Use a drm_device pointer instead of device pointer in prototype
> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> ---
>   drivers/gpu/drm/drm_gem_cma_helper.c | 55 ++++++++++++++++++++++++++++
>   include/drm/drm_gem_cma_helper.h     |  5 +++
>   2 files changed, 60 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
> index 235c7a63da2b..41f309e0e049 100644
> --- a/drivers/gpu/drm/drm_gem_cma_helper.c
> +++ b/drivers/gpu/drm/drm_gem_cma_helper.c
> @@ -17,9 +17,14 @@
>   #include <linux/slab.h>
>   
>   #include <drm/drm.h>
> +#include <drm/drm_damage_helper.h>
>   #include <drm/drm_device.h>
>   #include <drm/drm_drv.h>
> +#include <drm/drm_fourcc.h>
> +#include <drm/drm_fb_cma_helper.h>

Alphabetical order:

fb < fourcc

> +#include <drm/drm_framebuffer.h>
>   #include <drm/drm_gem_cma_helper.h>
> +#include <drm/drm_plane.h>
>   #include <drm/drm_vma_manager.h>
>   
>   /**
> @@ -576,3 +581,53 @@ drm_gem_cma_prime_import_sg_table_vmap(struct drm_device *dev,
>   	return obj;
>   }
>   EXPORT_SYMBOL(drm_gem_cma_prime_import_sg_table_vmap);
> +
> +/**
> + * drm_gem_cma_sync_data - Sync GEM object to non-coherent backing memory
> + * @drm: DRM device
> + * @old_state: Old plane state
> + * @state: New plane state
> + *
> + * This function can be used by drivers that use damage clips and have
> + * CMA GEM objects backed by non-coherent memory. Calling this function
> + * in a plane's .atomic_update ensures that all the data in the backing
> + * memory have been written to RAM.
> + */
> +void drm_gem_cma_sync_data(struct drm_device *drm,
> +			   struct drm_plane_state *old_state,
> +			   struct drm_plane_state *state)
> +{
> +	const struct drm_format_info *finfo = state->fb->format;
> +	struct drm_atomic_helper_damage_iter iter;
> +	const struct drm_gem_cma_object *cma_obj;
> +	unsigned int offset, i;
> +	struct drm_rect clip;
> +	dma_addr_t daddr;
> +
> +	for (i = 0; i < finfo->num_planes; i++) {
> +		cma_obj = drm_fb_cma_get_gem_obj(state->fb, i);
> +
> +		if (cma_obj->map_noncoherent)
> +			break;
> +	}
> +
> +	/* No non-coherent buffers - no need to sync anything. */
> +	if (i == finfo->num_planes)
> +		return;
> +
> +	drm_atomic_helper_damage_iter_init(&iter, old_state, state);
> +
> +	drm_atomic_for_each_plane_damage(&iter, &clip) {
> +		for (i = 0; i < finfo->num_planes; i++) {
> +			daddr = drm_fb_cma_get_gem_addr(state->fb, state, i);
> +
> +			/* Ignore x1/x2 values, invalidate complete lines */
> +			offset = clip.y1 * state->fb->pitches[i];
> +
> +			dma_sync_single_for_device(drm->dev, daddr + offset,
> +				       (clip.y2 - clip.y1) * state->fb->pitches[i],
> +				       DMA_TO_DEVICE);

A framebuffer can have multiple BOs with different coherency. The 
current loop syncs every BO, but you only have to sync non-coherent memory.

I suggest to merge the above test loop into this sync loop, such that 
only non-coherent BOs get synced

damage_iter_init(iter)

for_each_damage_plane(iter) {
   for (i < finfo->num_planes) {
     cma_obj = drm_fb_cma_get_gem_obj(i)
     if (!cma_obj->non_coherent)
       continue;
     dma_sync_single_for_device()
   }
}

For cache locality, it might be better to exchange the loops:

for (i < finfo->num_planes) {

   damage_iter_init(iter)
   for_each_damage_plane(iter) {


   }
}

This way, you operate on the BOs one by one.

> +		}
> +	}
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_cma_sync_data);
> diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
> index cd13508acbc1..76af066ae3a7 100644
> --- a/include/drm/drm_gem_cma_helper.h
> +++ b/include/drm/drm_gem_cma_helper.h
> @@ -7,6 +7,7 @@
>   #include <drm/drm_gem.h>
>   
>   struct drm_mode_create_dumb;
> +struct drm_plane_state;
>   
>   /**
>    * struct drm_gem_cma_object - GEM object backed by CMA memory allocations
> @@ -185,4 +186,8 @@ drm_gem_cma_prime_import_sg_table_vmap(struct drm_device *drm,
>   				       struct dma_buf_attachment *attach,
>   				       struct sg_table *sgt);
>   
> +void drm_gem_cma_sync_data(struct drm_device *drm,
> +			   struct drm_plane_state *old_state,
> +			   struct drm_plane_state *state);
> +

Maybe call this function drm_gem_cma_sync_non_coherent() so that it's 
clear what the sync is about.

Best regards
Thomas

>   #endif /* __DRM_GEM_CMA_HELPER_H__ */
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer


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