• David Herrmann's avatar
    drm/gem: remove misleading gfp parameter to get_pages() · 0cdbe8ac
    David Herrmann authored
    drm_gem_get_pages() currently allows passing a 'gfp' parameter that is
    passed to shmem combined with mapping_gfp_mask(). Given that the default
    mapping_gfp_mask() is GFP_HIGHUSER, it is _very_ unlikely that anyone will
    ever make use of that parameter. In fact, all drivers currently pass
    redundant flags or 0.
    
    This patch removes the 'gfp' parameter. The only reason to keep it is to
    remove flags like __GFP_WAIT. But in its current form, it can only be used
    to add flags. So to remove __GFP_WAIT, you'd have to drop it from the
    mapping_gfp_mask, which again is stupid as this mask is used by shmem-core
    for other allocations, too.
    
    If any driver ever requires that parameter, we can introduce a new helper
    that takes the raw 'gfp' parameter. The caller'd be responsible to combine
    it with mapping_gfp_mask() in a suitable way. The current
    drm_gem_get_pages() helper would then simply use mapping_gfp_mask() and
    call the new helper. This is what shmem_read_mapping_pages{_gfp,} does
    right now.
    
    Moreover, the gfp-zone flag-usage is not obvious: If you pass a modified
    zone, shmem core will WARN() or even BUG(). In other words, the following
    must be true for 'gfp' passed to shmem_read_mapping_pages_gfp():
        gfp_zone(mapping_gfp_mask(mapping)) == gfp_zone(gfp)
    Add a comment to drm_gem_read_pages() explaining that constraint.
    Signed-off-by: default avatarDavid Herrmann <dh.herrmann@gmail.com>
    0cdbe8ac
gtt.c 15.5 KB