LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Robert Beckett <bob.beckett@collabora.com>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>
Cc: "Matthew Auld" <matthew.auld@intel.com>,
	"Ramalingam C" <ramalingam.c@intel.com>,
	"Robert Beckett" <bob.beckett@collabora.com>,
	"Jordan Justen" <jordan.l.justen@intel.com>,
	"Thomas Hellström" <thomas.hellstrom@linux.intel.com>,
	"Simon Ser" <contact@emersion.fr>,
	"Pekka Paalanen" <ppaalanen@gmail.com>,
	"Kenneth Graunke" <kenneth@whitecape.org>,
	mesa-dev@lists.freedesktop.org, "Tony Ye" <tony.ye@intel.com>,
	"Slawomir Milczarek" <slawomir.milczarek@intel.com>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v8 5/5] drm/i915/uapi: document behaviour for DG2 64K support
Date: Tue,  8 Feb 2022 20:34:19 +0000	[thread overview]
Message-ID: <20220208203419.1094362-6-bob.beckett@collabora.com> (raw)
In-Reply-To: <20220208203419.1094362-1-bob.beckett@collabora.com>

From: Matthew Auld <matthew.auld@intel.com>

On discrete platforms like DG2, we need to support a minimum page size
of 64K when dealing with device local-memory. This is quite tricky for
various reasons, so try to document the new implicit uapi for this.

v3: fix typos and less emphasis
v2: Fixed suggestions on formatting [Daniel]

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
Acked-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
cc: Simon Ser <contact@emersion.fr>
cc: Pekka Paalanen <ppaalanen@gmail.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Cc: mesa-dev@lists.freedesktop.org
Cc: Tony Ye <tony.ye@intel.com>
Cc: Slawomir Milczarek <slawomir.milczarek@intel.com>
---
 include/uapi/drm/i915_drm.h | 44 ++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 5e678917da70..77e5e74c32c1 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -1118,10 +1118,16 @@ struct drm_i915_gem_exec_object2 {
 	/**
 	 * When the EXEC_OBJECT_PINNED flag is specified this is populated by
 	 * the user with the GTT offset at which this object will be pinned.
+	 *
 	 * When the I915_EXEC_NO_RELOC flag is specified this must contain the
 	 * presumed_offset of the object.
+	 *
 	 * During execbuffer2 the kernel populates it with the value of the
 	 * current GTT offset of the object, for future presumed_offset writes.
+	 *
+	 * See struct drm_i915_gem_create_ext for the rules when dealing with
+	 * alignment restrictions with I915_MEMORY_CLASS_DEVICE, on devices with
+	 * minimum page sizes, like DG2.
 	 */
 	__u64 offset;
 
@@ -3145,11 +3151,39 @@ struct drm_i915_gem_create_ext {
 	 *
 	 * The (page-aligned) allocated size for the object will be returned.
 	 *
-	 * Note that for some devices we have might have further minimum
-	 * page-size restrictions(larger than 4K), like for device local-memory.
-	 * However in general the final size here should always reflect any
-	 * rounding up, if for example using the I915_GEM_CREATE_EXT_MEMORY_REGIONS
-	 * extension to place the object in device local-memory.
+	 *
+	 * DG2 64K min page size implications:
+	 *
+	 * On discrete platforms, starting from DG2, we have to contend with GTT
+	 * page size restrictions when dealing with I915_MEMORY_CLASS_DEVICE
+	 * objects.  Specifically the hardware only supports 64K or larger GTT
+	 * page sizes for such memory. The kernel will already ensure that all
+	 * I915_MEMORY_CLASS_DEVICE memory is allocated using 64K or larger page
+	 * sizes underneath.
+	 *
+	 * Note that the returned size here will always reflect any required
+	 * rounding up done by the kernel, i.e 4K will now become 64K on devices
+	 * such as DG2.
+	 *
+	 * Special DG2 GTT address alignment requirement:
+	 *
+	 * The GTT alignment will also need to be at least 2M for such objects.
+	 *
+	 * Note that due to how the hardware implements 64K GTT page support, we
+	 * have some further complications:
+	 *
+	 *   1) The entire PDE (which covers a 2MB virtual address range), must
+	 *   contain only 64K PTEs, i.e mixing 4K and 64K PTEs in the same
+	 *   PDE is forbidden by the hardware.
+	 *
+	 *   2) We still need to support 4K PTEs for I915_MEMORY_CLASS_SYSTEM
+	 *   objects.
+	 *
+	 * To keep things simple for userland, we mandate that any GTT mappings
+	 * must be aligned to and rounded up to 2MB. As this only wastes virtual
+	 * address space and avoids userland having to copy any needlessly
+	 * complicated PDE sharing scheme (coloring) and only affects DG2, this
+	 * is deemed to be a good compromise.
 	 */
 	__u64 size;
 	/**
-- 
2.25.1


  parent reply	other threads:[~2022-02-08 22:34 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20220208203419.1094362-1-bob.beckett@collabora.com>
2022-02-08 20:34 ` [PATCH v8 1/5] drm/i915: add needs_compact_pt flag Robert Beckett
2022-02-08 20:34 ` [PATCH v8 2/5] drm/i915: enforce min GTT alignment for discrete cards Robert Beckett
2022-02-08 20:34 ` [PATCH v8 3/5] drm/i915: support 64K GTT pages " Robert Beckett
2022-02-08 20:34 ` [PATCH v8 4/5] drm/i915: add gtt misalignment test Robert Beckett
2022-02-08 20:34 ` Robert Beckett [this message]
2022-02-18  4:57   ` [PATCH v8 5/5] drm/i915/uapi: document behaviour for DG2 64K support Jordan Justen
2022-02-18 13:47     ` Ramalingam C
2022-02-18 18:06       ` Robert Beckett
2022-02-18 18:55         ` Ramalingam C
2022-02-18 19:42           ` Jordan Justen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20220208203419.1094362-6-bob.beckett@collabora.com \
    --to=bob.beckett@collabora.com \
    --cc=airlied@linux.ie \
    --cc=contact@emersion.fr \
    --cc=daniel@ffwll.ch \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=intel-gfx@lists.freedesktop.org \
    --cc=jani.nikula@linux.intel.com \
    --cc=joonas.lahtinen@linux.intel.com \
    --cc=jordan.l.justen@intel.com \
    --cc=kenneth@whitecape.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=matthew.auld@intel.com \
    --cc=mesa-dev@lists.freedesktop.org \
    --cc=ppaalanen@gmail.com \
    --cc=ramalingam.c@intel.com \
    --cc=rodrigo.vivi@intel.com \
    --cc=slawomir.milczarek@intel.com \
    --cc=thomas.hellstrom@linux.intel.com \
    --cc=tony.ye@intel.com \
    --cc=tvrtko.ursulin@linux.intel.com \
    --subject='Re: [PATCH v8 5/5] drm/i915/uapi: document behaviour for DG2 64K support' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).