From 648a9bc5308d952f2c80772301b339f73026f013 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Thu, 16 Jul 2015 12:37:56 +0100 Subject: [PATCH] drm/i915: Use two 32bit reads for select 64bit REG_READ ioctls MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Since the hardware sometimes mysteriously totally flummoxes the 64bit read of a 64bit register when read using a single instruction, split the read into two instructions. Since the read here is of automatically incrementing timestamp counters, we also have to be very careful in order to make sure that it does not increment between the two instructions. However, since userspace tried to workaround this issue and so enshrined this ABI for a broken hardware read and in the process neglected that the read only fails in some environments, we have to introduce a new uABI flag for userspace to request the 2x32 bit accurate read of the timestamp. v2: Fix alignment check and include details of the workaround for userspace. Reported-by: Karol Herbst Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91317 Testcase: igt/gem_reg_read Signed-off-by: Chris Wilson Cc: Michał Winiarski Cc: stable@vger.kernel.org Tested-by: Michał Winiarski Signed-off-by: Daniel Vetter --- Reading git-format-patch failed