Re: [Intel-gfx] [PATCH v3] drm/i915/ttm: implement access_memory

[Andi Shyti <andi.shyti@linux.intel.com>]

Hi Matt,

On Mon, Oct 03, 2022 at 06:28:19PM +0100, 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.
> 
> v2:
>   - ttm_bo_kmap doesn't seem to work well here, and seems to expect
>     contiguous resource.
> v3(Andi):
>   - s/PAGE_SIZE/bytes/ when passing in the size of the mapping.
> 
> References: https://gitlab.freedesktop.org/drm/intel/-/issues/6989
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Cc: Nirmoy Das <nirmoy.das@intel.com>
> Cc: Andi Shyti <andi.shyti@linux.intel.com>

Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>

Thanks,
Andi

> ---
>  drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 45 +++++++++++++++++++++++++
>  1 file changed, 45 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..d11cd9c57247 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -699,6 +699,50 @@ 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)
> +{
> +	struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
> +	resource_size_t iomap = obj->mm.region->iomap.base -
> +		obj->mm.region->region.start;
> +	unsigned long page = offset >> PAGE_SHIFT;
> +	unsigned long bytes_left = len;
> +
> +	/*
> +	 * 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).
> +	 */
> +	if (!i915_ttm_resource_mappable(bo->resource))
> +		return -EIO;
> +
> +	offset -= page << PAGE_SHIFT;
> +	do {
> +		unsigned long bytes = min(bytes_left, PAGE_SIZE - offset);
> +		void __iomem *ptr;
> +		dma_addr_t daddr;
> +
> +		daddr = i915_gem_object_get_dma_address(obj, page);
> +		ptr = ioremap_wc(iomap + daddr + offset, bytes);
> +		if (!ptr)
> +			return -EIO;
> +
> +		if (write)
> +			memcpy_toio(ptr, buf, bytes);
> +		else
> +			memcpy_fromio(buf, ptr, bytes);
> +		iounmap(ptr);
> +
> +		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 +759,7 @@ 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,
>  };
>  
>  /**
> -- 
> 2.37.3