Why do flush page cache twice when change TT's cache attribute

[Jerome Glisse]

On Mon, 2012-03-19 at 23:11 +0800, Scott Fang wrote:
> In function ttm_tt_set_caching
> ,,,,,,,
> 
>     if (ttm->caching_state == tt_cached)
>         drm_clflush_pages(ttm->pages, ttm->num_pages);
> 
>     for (i = 0; i < ttm->num_pages; ++i) {
>         cur_page = ttm->pages[i];
>         if (likely(cur_page != NULL)) {
>             ret = ttm_tt_set_page_caching(cur_page,
>                               ttm->caching_state,
>                               c_state);
>             if (unlikely(ret != 0))
>                 goto out_err;
>         }
>     }
> 
>     ttm->caching_state = c_state;
> 
>     return 0;
> 
> 
> drm_clflush_pages flush cache one time.
> then in the following function
> ttm_tt_set_page_caching->set_memory_wc->change_page_attr_set: in this
> function may flush page cache again.
> 
> Does the code do some abundant flush, or there is some trick to these
> codes?
> 
> Thanks for the answer in advance.

Yes there might be redundant flushing.

Cheers,
Jerome