drm/i915/gt: Keep a no-frills swappable copy of the default context state

We need to keep the default context state around to instantiate new
contexts (aka golden rendercontext), and we also keep it pinned while
the engine is active so that we can quickly reset a hanging context.
However, the default contexts are large enough to merit keeping in
swappable memory as opposed to kernel memory, so we store them inside
shmemfs. Currently, we use the normal GEM objects to create the default
context image, but we can throw away all but the shmemfs file.

This greatly simplifies the tricky power management code which wants to
run underneath the normal GT locking, and we definitely do not want to
use any high level objects that may appear to recurse back into the GT.
Though perhaps the primary advantage of the complex GEM object is that
we aggressively cache the mapping, but here we are recreating the
vm_area everytime time we unpark. At the worst, we add a lightweight
cache, but first find a microbenchmark that is impacted.

Having started to create some utility functions to make working with
shmemfs objects easier, we can start putting them to wider use, where
GEM objects are overkill, such as storing persistent error state.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429172429.6054-1-chris@chris-wilson.co.uk

1 files changed, 23 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.h b/drivers/gpu/drm/i915/gt/shmem_utils.h
new file mode 100644
index 000000000000..c1669170c351
--- /dev/null
+++ b/drivers/gpu/drm/i915/gt/shmem_utils.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2020 Intel Corporation
+ */
+
+#ifndef SHMEM_UTILS_H
+#define SHMEM_UTILS_H
+
+#include <linux/types.h>
+
+struct drm_i915_gem_object;
+struct file;
+
+struct file *shmem_create_from_data(const char *name, void *data, size_t len);
+struct file *shmem_create_from_object(struct drm_i915_gem_object *obj);
+
+void *shmem_pin_map(struct file *file);
+void shmem_unpin_map(struct file *file, void *ptr);
+
+int shmem_read(struct file *file, loff_t off, void *dst, size_t len);
+int shmem_write(struct file *file, loff_t off, void *src, size_t len);
+
+#endif /* SHMEM_UTILS_H */