This is not complete documentation, but covers the pieces I read through
while reviewing the IGT CRC tests for nouveau. It covers the
nouveau-specific debugfs file, an overview of why the code is more
complicated than the DRM display CRC support documentation would lead
one to expect, and the nv50_crc_func vtable. Many of the details were
gleaned from Lyude's commit message, but I think it's valuable to have
them with the code rather than in the change log.
The rendered documentation of the functions in nv50_crc_func aren't as
nice as I'd like, but from what I can tell it would require creating a
typedef for each function with proper argument/return value docs.
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Signed-off-by: Jeremy Cline <jcline@xxxxxxxxxx>
---
drivers/gpu/drm/nouveau/dispnv50/crc.c | 8 ++++
drivers/gpu/drm/nouveau/dispnv50/crc.h | 65 ++++++++++++++++++++++++++
2 files changed, 73 insertions(+)
diff --git a/drivers/gpu/drm/nouveau/dispnv50/crc.c b/drivers/gpu/drm/nouveau/dispnv50/crc.c
index b8c31b697797..84df41e8fb05 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/crc.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/crc.c
@@ -699,6 +699,14 @@ nv50_crc_debugfs_flip_threshold_set(struct file *file,
return ret;
}
+/**
+ * DOC: nv_crc/flip_threshold
+ *
+ * The number of CRC entries to place in a :term:`CRC notifier context` before
+ * attempting to flip to the other notifier context. Writing ``-1`` to this file
+ * will reset the threshold to the default value, which is hardware-dependent.
+ * Values cannot be greater than the default or less than ``-1``.
+ */
static const struct file_operations nv50_crc_flip_threshold_fops = {
.owner = THIS_MODULE,
.open = nv50_crc_debugfs_flip_threshold_open,
diff --git a/drivers/gpu/drm/nouveau/dispnv50/crc.h b/drivers/gpu/drm/nouveau/dispnv50/crc.h
index 4fce871b04c8..04ebb1f936db 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/crc.h
+++ b/drivers/gpu/drm/nouveau/dispnv50/crc.h
@@ -10,6 +10,24 @@
#include <nvkm/subdev/bios.h>
#include "nouveau_encoder.h"
+/**
+ * DOC: Overview
+ *
+ * This interface is designed to aid in the implementation of the standard DRM
+ * CRC interface that is part of :doc:`drm-uapi`. NVIDIA's hardware has a
+ * peculiar CRC implementation that limits the number of CRCs that can be
+ * captured, which breaks the DRM API's expectations.
+ *
+ * CRCs are reported to a :term:`CRC notifier context` of limited size. Once the
+ * context fills, an overflow bit is set and no further CRCs are reported. To
+ * work around this, the driver flips between notifier contexts to allow users
+ * to capture an arbitrary number of CRCs.
+ *
+ * .. warning:: The flip requires flushing two separate updates on the
+ * :term:`EVO/NVD` channel, and this results in the unavoidable loss of a single
+ * frame's CRC.
+ */
+
struct nv50_atom;
struct nv50_disp;
struct nv50_head;
@@ -49,16 +67,63 @@ struct nv50_crc_atom {
u8 wndw : 4;
};
+/**
+ * struct nv50_crc_func - Functions and data for CRC support
+ *
+ * The interface used to abstract CRC support across card families that support
+ * it.
+ */
struct nv50_crc_func {
+ /**
+ * @set_src: Program the hardware to capture CRCs from the given
+ * &enum nv50_crc_source_type. Using NULL for the source and ctx will
+ * disable CRC for the given &struct nv50_head.
+ *
+ * Return 0 on success, or a negative error code.
+ */
int (*set_src)(struct nv50_head *, int or, enum nv50_crc_source_type,
struct nv50_crc_notifier_ctx *, u32 wndw);
+
+ /**
+ * @set_ctx: Change the &struct nv50_crc_notifier_ctx used to capture
+ * CRC entries. Providing a NULL context will remove any existing
+ * context.
+ *
+ * Return 0 on success, or a negative error code.
+ */
int (*set_ctx)(struct nv50_head *, struct nv50_crc_notifier_ctx *);
+
+ /**
+ * @get_entry: Read the CRC entry at the given index. idx is guaranteed
+ * to be less than @num_entries so implementations do not need to
+ * perform a bounds check.
+ *
+ * Return the CRC or 0 if there is no CRC for the given index.
+ */
u32 (*get_entry)(struct nv50_head *, struct nv50_crc_notifier_ctx *,
enum nv50_crc_source, int idx);
+
+ /**
+ * @ctx_finished: Return true when all requested CRCs have been written
+ * and it is safe to read them.
+ */
bool (*ctx_finished)(struct nv50_head *,
struct nv50_crc_notifier_ctx *);
+
+ /**
+ * @flip_threshold: The default number of CRC entries at which point the
+ * notifier context should be flipped. This should be set somewhat lower
+ * than @num_entries. It is configurable from userspace via DebugFS.
+ */
short flip_threshold;
+
+ /**
+ * @num_entries: The maximum number of entries supported in the
+ * notifier context.
+ */
short num_entries;
+
+ /** @notifier_len: The size of the notifier context in bytes. */
size_t notifier_len;
};
--
2.28.0
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