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2024-10-12 a5969cabbb4660eab42b6ef0412cbbd1200cf14d 
 kernel/Documentation/gpu/drm-uapi.rst
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+.. Copyright 2020 DisplayLink (UK) Ltd.
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+
13 ===================
24 Userland interfaces
35 ===================
....@@ -85,16 +87,18 @@
8587 - The userspace side must be fully reviewed and tested to the standards of that
8688   userspace project. For e.g. mesa this means piglit testcases and review on the
8789   mailing list. This is again to ensure that the new interface actually gets the
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-  job done.
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+  job done.  The userspace-side reviewer should also provide an Acked-by on the
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+  kernel uAPI patch indicating that they believe the proposed uAPI is sound and
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+  sufficiently documented and validated for userspace's consumption.
8993 
9094 - The userspace patches must be against the canonical upstream, not some vendor
9195   fork. This is to make sure that no one cheats on the review and testing
9296   requirements by doing a quick fork.
9397 
9498 - The kernel patch can only be merged after all the above requirements are met,
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-  but it **must** be merged **before** the userspace patches land. uAPI always flows
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-  from the kernel, doing things the other way round risks divergence of the uAPI
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-  definitions and header files.
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+  but it **must** be merged to either drm-next or drm-misc-next **before** the
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+  userspace patches land. uAPI always flows from the kernel, doing things the
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+  other way round risks divergence of the uAPI definitions and header files.
98102 
99103 These are fairly steep requirements, but have grown out from years of shared
100104 pain and experience with uAPI added hastily, and almost always regretted about
....@@ -160,6 +164,116 @@
160164 visible to user-space and accessible beyond open-file boundaries, they
161165 cannot support render nodes.
162166 
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+Device Hot-Unplug
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+=================
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+
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+.. note::
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+   The following is the plan. Implementation is not there yet
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+   (2020 May).
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+
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+Graphics devices (display and/or render) may be connected via USB (e.g.
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+display adapters or docking stations) or Thunderbolt (e.g. eGPU). An end
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+user is able to hot-unplug this kind of devices while they are being
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+used, and expects that the very least the machine does not crash. Any
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+damage from hot-unplugging a DRM device needs to be limited as much as
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+possible and userspace must be given the chance to handle it if it wants
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+to. Ideally, unplugging a DRM device still lets a desktop continue to
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+run, but that is going to need explicit support throughout the whole
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+graphics stack: from kernel and userspace drivers, through display
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+servers, via window system protocols, and in applications and libraries.
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+
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+Other scenarios that should lead to the same are: unrecoverable GPU
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+crash, PCI device disappearing off the bus, or forced unbind of a driver
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+from the physical device.
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+
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+In other words, from userspace perspective everything needs to keep on
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+working more or less, until userspace stops using the disappeared DRM
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+device and closes it completely. Userspace will learn of the device
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+disappearance from the device removed uevent, ioctls returning ENODEV
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+(or driver-specific ioctls returning driver-specific things), or open()
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+returning ENXIO.
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+
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+Only after userspace has closed all relevant DRM device and dmabuf file
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+descriptors and removed all mmaps, the DRM driver can tear down its
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+instance for the device that no longer exists. If the same physical
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+device somehow comes back in the mean time, it shall be a new DRM
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+device.
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+
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+Similar to PIDs, chardev minor numbers are not recycled immediately. A
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+new DRM device always picks the next free minor number compared to the
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+previous one allocated, and wraps around when minor numbers are
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+exhausted.
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+
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+The goal raises at least the following requirements for the kernel and
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+drivers.
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+
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+Requirements for KMS UAPI
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+-------------------------
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+
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+- KMS connectors must change their status to disconnected.
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+
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+- Legacy modesets and pageflips, and atomic commits, both real and
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+  TEST_ONLY, and any other ioctls either fail with ENODEV or fake
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+  success.
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+
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+- Pending non-blocking KMS operations deliver the DRM events userspace
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+  is expecting. This applies also to ioctls that faked success.
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+
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+- open() on a device node whose underlying device has disappeared will
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+  fail with ENXIO.
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+
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+- Attempting to create a DRM lease on a disappeared DRM device will
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+  fail with ENODEV. Existing DRM leases remain and work as listed
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+  above.
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+
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+Requirements for Render and Cross-Device UAPI
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+---------------------------------------------
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+
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+- All GPU jobs that can no longer run must have their fences
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+  force-signalled to avoid inflicting hangs on userspace.
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+  The associated error code is ENODEV.
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+
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+- Some userspace APIs already define what should happen when the device
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+  disappears (OpenGL, GL ES: `GL_KHR_robustness`_; `Vulkan`_:
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+  VK_ERROR_DEVICE_LOST; etc.). DRM drivers are free to implement this
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+  behaviour the way they see best, e.g. returning failures in
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+  driver-specific ioctls and handling those in userspace drivers, or
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+  rely on uevents, and so on.
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+
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+- dmabuf which point to memory that has disappeared will either fail to
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+  import with ENODEV or continue to be successfully imported if it would
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+  have succeeded before the disappearance. See also about memory maps
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+  below for already imported dmabufs.
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+
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+- Attempting to import a dmabuf to a disappeared device will either fail
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+  with ENODEV or succeed if it would have succeeded without the
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+  disappearance.
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+
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+- open() on a device node whose underlying device has disappeared will
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+  fail with ENXIO.
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+
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+.. _GL_KHR_robustness: https://www.khronos.org/registry/OpenGL/extensions/KHR/KHR_robustness.txt
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+.. _Vulkan: https://www.khronos.org/vulkan/
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+
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+Requirements for Memory Maps
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+----------------------------
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+
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+Memory maps have further requirements that apply to both existing maps
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+and maps created after the device has disappeared. If the underlying
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+memory disappears, the map is created or modified such that reads and
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+writes will still complete successfully but the result is undefined.
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+This applies to both userspace mmap()'d memory and memory pointed to by
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+dmabuf which might be mapped to other devices (cross-device dmabuf
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+imports).
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+
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+Raising SIGBUS is not an option, because userspace cannot realistically
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+handle it. Signal handlers are global, which makes them extremely
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+difficult to use correctly from libraries like those that Mesa produces.
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+Signal handlers are not composable, you can't have different handlers
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+for GPU1 and GPU2 from different vendors, and a third handler for
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+mmapped regular files. Threads cause additional pain with signal
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+handling as well.
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+
163277 .. _drm_driver_ioctl:
164278 
165279 IOCTL Support on Device Nodes
....@@ -190,13 +304,16 @@
190304 
191305         Simply running out of kernel/system memory is signalled through ENOMEM.
192306 
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-EPERM/EACCESS:
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+EPERM/EACCES:
194308         Returned for an operation that is valid, but needs more privileges.
195309         E.g. root-only or much more common, DRM master-only operations return
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-        this when when called by unpriviledged clients. There's no clear
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-        difference between EACCESS and EPERM.
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+        this when called by unpriviledged clients. There's no clear
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+        difference between EACCES and EPERM.
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199313 ENODEV:
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+        The device is not present anymore or is not yet fully initialized.
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+
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+EOPNOTSUPP:
200317         Feature (like PRIME, modesetting, GEM) is not supported by the driver.
201318 
202319 ENXIO:
....@@ -235,42 +352,59 @@
235352 Testing and validation
236353 ======================
237354 
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+Testing Requirements for userspace API
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+--------------------------------------
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+
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+New cross-driver userspace interface extensions, like new IOCTL, new KMS
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+properties, new files in sysfs or anything else that constitutes an API change
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+should have driver-agnostic testcases in IGT for that feature, if such a test
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+can be reasonably made using IGT for the target hardware.
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+
238363 Validating changes with IGT
239364 ---------------------------
240365 
241366 There's a collection of tests that aims to cover the whole functionality of
242367 DRM drivers and that can be used to check that changes to DRM drivers or the
243368 core don't regress existing functionality. This test suite is called IGT and
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-its code can be found in https://cgit.freedesktop.org/drm/igt-gpu-tools/.
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+its code and instructions to build and run can be found in
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+https://gitlab.freedesktop.org/drm/igt-gpu-tools/.
245371 
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-To build IGT, start by installing its build dependencies. In Debian-based
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-systems::
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+Using VKMS to test DRM API
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+--------------------------
248374 
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-	# apt-get build-dep intel-gpu-tools
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+VKMS is a software-only model of a KMS driver that is useful for testing
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+and for running compositors. VKMS aims to enable a virtual display without
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+the need for a hardware display capability. These characteristics made VKMS
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+a perfect tool for validating the DRM core behavior and also support the
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+compositor developer. VKMS makes it possible to test DRM functions in a
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+virtual machine without display, simplifying the validation of some of the
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+core changes.
250382 
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-And in Fedora-based systems::
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+To Validate changes in DRM API with VKMS, start setting the kernel: make
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+sure to enable VKMS module; compile the kernel with the VKMS enabled and
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+install it in the target machine. VKMS can be run in a Virtual Machine
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+(QEMU, virtme or similar). It's recommended the use of KVM with the minimum
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+of 1GB of RAM and four cores.
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-	# dnf builddep intel-gpu-tools
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+It's possible to run the IGT-tests in a VM in two ways:
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-Then clone the repository::
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+	1. Use IGT inside a VM
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+	2. Use IGT from the host machine and write the results in a shared directory.
256393 
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-	$ git clone git://anongit.freedesktop.org/drm/igt-gpu-tools
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+As follow, there is an example of using a VM with a shared directory with
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+the host machine to run igt-tests. As an example it's used virtme::
258396 
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-Configure the build system and start the build::
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+	$ virtme-run --rwdir /path/for/shared_dir --kdir=path/for/kernel/directory --mods=auto
260398 
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-	$ cd igt-gpu-tools && ./autogen.sh && make -j6
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+Run the igt-tests in the guest machine, as example it's ran the 'kms_flip'
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+tests::
262401 
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-Download the piglit dependency::
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+	$ /path/for/igt-gpu-tools/scripts/run-tests.sh -p -s -t "kms_flip.*" -v
264403 
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-	$ ./scripts/run-tests.sh -d
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-
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-And run the tests::
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-
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-	$ ./scripts/run-tests.sh -t kms -t core -s
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-
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-run-tests.sh is a wrapper around piglit that will execute the tests matching
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-the -t options. A report in HTML format will be available in
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-./results/html/index.html. Results can be compared with piglit.
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+In this example, instead of build the igt_runner, Piglit is used
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+(-p option); it's created html summary of the tests results and it's saved
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+in the folder "igt-gpu-tools/results"; it's executed only the igt-tests
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+matching the -t option.
274408 
275409 Display CRC Support
276410 -------------------
....@@ -316,3 +450,12 @@
316450     mode setting, since on many devices the vertical blank counter is
317451     reset to 0 at some point during modeset. Modern drivers should not
318452     call this any more since with kernel mode setting it is a no-op.
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+
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+Userspace API Structures
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+========================
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+
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+.. kernel-doc:: include/uapi/drm/drm_mode.h
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+   :doc: overview
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+
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+.. kernel-doc:: include/uapi/drm/drm_mode.h
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+   :internal: