drm/edid: Switch DDC when reading the EDID
Originally by Seth Forshee <seth.forshee@canonical.com>, 2012-10-04: Some dual graphics machines support muxing the DDC separately from the display, so make use of this functionality when reading the EDID on the inactive GPU. Also serialize drm_get_edid() with a mutex to avoid races on the DDC mux state. Modified by Dave Airlie <airlied@gmail.com>, 2012-12-22: I can't figure out why I didn't like this, but I rewrote this [...] to lock/unlock the ddc lines [...]. I think I'd prefer something like that otherwise the interface got really ugly. Modified by Lukas Wunner <lukas@wunner.de>, 2015-04 - 2015-09: v3: Move vga_switcheroo calls to a wrapper around drm_get_edid() which drivers can call on muxed machines. This avoids other drivers having to go through the vga_switcheroo motions even though they are never used on a muxed platform (Thierry Reding, Daniel Vetter, Alex Deucher) Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115Tested-by: Pierre Moreau <pierre.morrow@free.fr> [MBP 5,3 2009 nvidia MCP79 + G96 pre-retina 15"] Tested-by: William Brown <william@blackhats.net.au> [MBP 8,2 2011 intel SNB + amd turks pre-retina 15"] Tested-by: Lukas Wunner <lukas@wunner.de> [MBP 9,1 2012 intel IVB + nvidia GK107 pre-retina 15"] Cc: Seth Forshee <seth.forshee@canonical.com> Cc: Dave Airlie <airlied@gmail.com> Signed-off-by: Lukas Wunner <lukas@wunner.de> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: http://patchwork.freedesktop.org/patch/msgid/b898d0da4c134f2642d0122479006863e1830723.1452525860.git.lukas@wunner.de
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