• Ben Widawsky's avatar
    Revert "drm/i915: Calculate correct stolen size for GEN7+" · c4ae25ec
    Ben Widawsky authored
    This reverts commit 03752f5b.
    
    This revert requires a bit of explanation on how I understand things
    work. Internally the architects/designers decide how the stolen encoding
    works. We put it in a doc. BIOS writers take these docs and implement
    it. Driver writers read the doc too, and read the value left by the BIOS
    writers, and then we make magic.
    
    The failing here is that in the docs we had[1] contained two different
    definitions for this register for Gen7. (We have both a PCI register,
    and an MMIO, and each of these were different). At the time [2] of
    03752f5b, we asked the architects what the correct value should be; but
    that doesn't match the reality (BIOS) unfortunately.
    
    So on all machines I can get my hands on, this revert is the right thing
    to do. I've also worked with the product group to confirm that they
    agree this revert is what we should do. People using HW made my "people"
    who both write their own BIOS, and have access to our docs (Apple?).
    Investigations are still ongoing about whether we need to add a list
    of machines needing special handling, but this patch should be the
    right thing for pretty much everyone.
    
    [1] The docs are still wrong on this one. Now instead of two registers with
    two definitions, we have one register with BOTH definitions, progress?
    [2] The open source PRMs have the "wrong" definitions in chapter Volume
    1 part6, section 1.1.12.
    
    This digging was inspired by Paulo.
    
    Cc: Paulo Zanoni <przanoni@gmail.com>
    Signed-off-by: default avatarBen Widawsky <ben@bwidawsk.net>
    Acked-by: default avatarJesse Barnes <jbarnes@virtuousgeek.org>
    [danvet: Augment the patch saying that it's still a bit unclear
    whether there are any machines out there with "wrong" firmware and
    whether we need to add a list to handle them specially.]
    Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    c4ae25ec
i915_gem_gtt.c 22.6 KB