Why does gbm need to tile and detile buffers?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/kernel/+/05928ac241af9b685d23d5026ccbc1006bd5cac0

commit 05928ac241af9b685d23d5026ccbc1006bd5cac0
Author: Sean Paul <seanpaul@chromium.org>
Date: Fri Jan 30 18:57:01 2015

BACKPORT: drm/tegra: gem: Return 64-bit offset for mmap(2)

On 64-bit targets, tegra_gem_mmap() only returns a partial offset to
userspace. As such, subsequent calls to mmap(2) may fail. Change the
arguments to use a 64-bit offset to fix this.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Acked-by: Erik Faye-Lund <kusmabite@gmail.com>
[treding@nvidia.com: tweak commit message]
Signed-off-by: Thierry Reding <treding@nvidia.com>

(cherry picked from commit bdf765071a8b573f7b1ba14c02881fa3e623825e)
Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>

BUG= chromium:673570 
TEST=gbm_bo_map(..) doesn't fail due differences between kernel uapi's
tegra_drm.h and libdrm's tegra_drm.h

Change-Id: Ibcd32b6350f86e5697aad2fac844f6907e3df51b
Reviewed-on: https://chromium-review.googlesource.com/419662
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>

[modify] https://crrev.com/05928ac241af9b685d23d5026ccbc1006bd5cac0/include/uapi/drm/tegra_drm.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/minigbm/+/5972eec261ea3f01dda53471e69ae7f2017bedf5

commit 5972eec261ea3f01dda53471e69ae7f2017bedf5
Author: Gurchetan Singh <gurchetansingh@chromium.org>
Date: Fri Dec 16 23:51:46 2016

minigbm: tegra: align linear buffers to 64-byte boundaries

Tegra20 and Tegra30 both required the buffer line stride to be aligned
on 8 byte boundaries. Tegra114 and Tegra124 increased the alignment to
64 bytes.

The kernel automatically does this for us for dumb buffers, but since the
tegra gem create API doesn't return the stride, we'll have to do it here.

BUG= chromium:673570 
TEST=tiled_bo_test succeeds

Change-Id: I2222f033813a31d3eed1a6794fbf044fba33eec0
Reviewed-on: https://chromium-review.googlesource.com/421278
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Haixia Shi <hshi@chromium.org>

[modify] https://crrev.com/5972eec261ea3f01dda53471e69ae7f2017bedf5/tegra.c

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/minigbm/+/44d1fe4264d4968cb8525f5e53f1fcd068dacbc2

commit 44d1fe4264d4968cb8525f5e53f1fcd068dacbc2
Author: Gurchetan Singh <gurchetansingh@chromium.org>
Date: Wed Dec 14 16:51:28 2016

minigbm: tegra: add blocklinear detiling logic

With CL:397941, hshi@ figured out how to detile blocklinear buffers
for tegra. Let's add that logic to our tegra map()/unmap() functions.
This can be useful for various tests.

BUG= chromium:673570 
TEST=tiled_bo_test draws ellipse texture on Tegra (there are artifacts
     due another bug though)

Change-Id: I7c2e7222ba67457ffd3641ba42a775ac4a667ec8
Reviewed-on: https://chromium-review.googlesource.com/421279
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Haixia Shi <hshi@chromium.org>

[modify] https://crrev.com/44d1fe4264d4968cb8525f5e53f1fcd068dacbc2/drv.c
[modify] https://crrev.com/44d1fe4264d4968cb8525f5e53f1fcd068dacbc2/drv_priv.h
[modify] https://crrev.com/44d1fe4264d4968cb8525f5e53f1fcd068dacbc2/tegra.c