Re: [PATCH 4/5] drm/i915: Add a partial GGTT view type

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 04/27/2015 03:50 PM, Tvrtko Ursulin wrote:
>> +    for_each_sg_page(obj->pages->sgl, &obj_sg_iter, obj->pages->nents,
>> +        view->params.partial.offset)
>> +    {
>> +        if (st->nents >= view->params.partial.size)
>> +            break;
>> +
>> +        sg_set_page(sg, NULL, PAGE_SIZE, 0);
>> +        sg_dma_address(sg) = sg_page_iter_dma_address(&obj_sg_iter);
>> +        sg_dma_len(sg) = PAGE_SIZE;
>> +
>> +        sg = sg_next(sg);
>> +        st->nents++;
>> +    }
>
> I suppose in this case (as opposed to rotated view) using
> sg_alloc_table_from_pages() could produce a more compact table. With the
> caveat of that it doesn't always work (see
> i915_gem_userptr.c/st_set_pages).
>
> So maybe promote to driver public st_set_pages and call in on an array
> of pages?

Scratch this, on second thought it makes no sense.

Only if we had a smarter helper like sg_alloc_table_from_table_range() 
but no one cared about coalescing in the past.

Regards,

Tvrtko

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