[Intel-gfx] [PATCH] drm/i915/ttm: implement access_memory

[Andrzej Hajda]

On 30.09.2022 17:25, Matthew Auld wrote:
> It looks like we need this for local-memory, if we want to use ptrace.
> Something more is still needed if we want to handle non-mappable memory,
> which looks quite annoying.
> 
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/6989
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Nirmoy Das <nirmoy.das at intel.com>

Reviewed-by: Andrzej Hajda <andrzej.hajda at intel.com>

Regards
Andrzej

> ---
>   drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 43 +++++++++++++++++++++++++
>   1 file changed, 43 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index 3dc6acfcf4ec..4f533e0c92b4 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -699,6 +699,48 @@ static unsigned long i915_ttm_io_mem_pfn(struct ttm_buffer_object *bo,
>   	return ((base + sg_dma_address(sg)) >> PAGE_SHIFT) + ofs;
>   }
>   
> +static int i915_ttm_access_memory(struct ttm_buffer_object *bo,
> +				  unsigned long offset, void *buf,
> +				  int len, int write)
> +{
> +	unsigned long page = offset >> PAGE_SHIFT;
> +	unsigned long bytes_left = len;
> +	int ret;
> +
> +	/*
> +	 * TODO: For now just let it fail if the resource is non-mappable,
> +	 * otherwise we need to perform the memcpy from the gpu here, without
> +	 * interfering with the object (like moving the entire thing).
> +	 */
> +
> +	offset -= page << PAGE_SHIFT;
> +	do {
> +		unsigned long bytes = min(bytes_left, PAGE_SIZE - offset);
> +		struct ttm_bo_kmap_obj map;
> +		void __iomem *ptr;
> +		bool is_iomem;
> +
> +		ret = ttm_bo_kmap(bo, page, 1, &map);
> +		if (ret)
> +			return ret;
> +
> +		ptr = ttm_kmap_obj_virtual(&map, &is_iomem) + offset;
> +		WARN_ON_ONCE(!is_iomem);
> +		if (write)
> +			memcpy_toio(ptr, buf, bytes);
> +		else
> +			memcpy_fromio(buf, ptr, bytes);
> +		ttm_bo_kunmap(&map);
> +
> +		page++;
> +		buf += bytes;
> +		bytes_left -= bytes;
> +		offset = 0;
> +	} while (bytes_left);
> +
> +	return len;
> +}
> +
>   /*
>    * All callbacks need to take care not to downcast a struct ttm_buffer_object
>    * without checking its subclass, since it might be a TTM ghost object.
> @@ -715,6 +757,7 @@ static struct ttm_device_funcs i915_ttm_bo_driver = {
>   	.delete_mem_notify = i915_ttm_delete_mem_notify,
>   	.io_mem_reserve = i915_ttm_io_mem_reserve,
>   	.io_mem_pfn = i915_ttm_io_mem_pfn,
> +	.access_memory = i915_ttm_access_memory,
>   };
>   
>   /**