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nouveau: Add lots of comments to the buffer transfer logic 

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
This commit is contained in:
Ilia Mirkin 2013-12-01 21:13:17 -05:00 committed by Maarten Lankhorst
parent 0e5bf85651
commit 06359e368b
2 changed files with 71 additions and 4 deletions
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71
src/gallium/drivers/nouveau/nouveau_buffer.c
View File

@ -129,6 +129,10 @@ nouveau_buffer_destroy(struct pipe_screen *pscreen,
NOUVEAU_DRV_STAT(nouveau_screen(pscreen), buf_obj_current_count, -1);
}
/* Set up a staging area for the transfer. This is either done in "regular"
* system memory if the driver supports push_data (nv50+) and the data is
* small enough (and permit_pb == true), or in GART memory.
*/
static uint8_t *
nouveau_transfer_staging(struct nouveau_context *nv,
struct nouveau_transfer *tx, boolean permit_pb)
@ -155,7 +159,10 @@ nouveau_transfer_staging(struct nouveau_context *nv,
return tx->map;
}
/* Maybe just migrate to GART right away if we actually need to do this. */
/* Copies data from the resource into the the transfer's temporary GART
* buffer. Also updates buf->data if present.
*
* Maybe just migrate to GART right away if we actually need to do this. */
static boolean
nouveau_transfer_read(struct nouveau_context *nv, struct nouveau_transfer *tx)
{
@ -210,7 +217,9 @@ nouveau_transfer_write(struct nouveau_context *nv, struct nouveau_transfer *tx,
nouveau_fence_ref(nv->screen->fence.current, &buf->fence_wr);
}
/* Does a CPU wait for the buffer's backing data to become reliably accessible
* for write/read by waiting on the buffer's relevant fences.
*/
static INLINE boolean
nouveau_buffer_sync(struct nv04_resource *buf, unsigned rw)
{
@ -283,6 +292,7 @@ nouveau_buffer_transfer_del(struct nouveau_context *nv,
}
}
/* Creates a cache in system memory of the buffer data. */
static boolean
nouveau_buffer_cache(struct nouveau_context *nv, struct nv04_resource *buf)
{
@ -317,6 +327,10 @@ nouveau_buffer_cache(struct nouveau_context *nv, struct nv04_resource *buf)
#define NOUVEAU_TRANSFER_DISCARD \
(PIPE_TRANSFER_DISCARD_RANGE | PIPE_TRANSFER_DISCARD_WHOLE_RESOURCE)
/* Checks whether it is possible to completely discard the memory backing this
* resource. This can be useful if we would otherwise have to wait for a read
* operation to complete on this data.
*/
static INLINE boolean
nouveau_buffer_should_discard(struct nv04_resource *buf, unsigned usage)
{
@ -327,6 +341,29 @@ nouveau_buffer_should_discard(struct nv04_resource *buf, unsigned usage)
return buf->mm && nouveau_buffer_busy(buf, PIPE_TRANSFER_WRITE);
}
/* Returns a pointer to a memory area representing a window into the
* resource's data.
*
* This may or may not be the _actual_ memory area of the resource. However
* when calling nouveau_buffer_transfer_unmap, if it wasn't the actual memory
* area, the contents of the returned map are copied over to the resource.
*
* The usage indicates what the caller plans to do with the map:
*
* WRITE means that the user plans to write to it
*
* READ means that the user plans on reading from it
*
* DISCARD_WHOLE_RESOURCE means that the whole resource is going to be
* potentially overwritten, and even if it isn't, the bits that aren't don't
* need to be maintained.
*
* DISCARD_RANGE means that all the data in the specified range is going to
* be overwritten.
*
* The strategy for determining what kind of memory area to return is complex,
* see comments inside of the function.
*/
static void *
nouveau_buffer_transfer_map(struct pipe_context *pipe,
struct pipe_resource *resource,
@ -352,11 +389,17 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
if (buf->domain == NOUVEAU_BO_VRAM) {
if (usage & NOUVEAU_TRANSFER_DISCARD) {
/* Set up a staging area for the user to write to. It will be copied
* back into VRAM on unmap. */
if (usage & PIPE_TRANSFER_DISCARD_WHOLE_RESOURCE)
buf->status &= NOUVEAU_BUFFER_STATUS_REALLOC_MASK;
nouveau_transfer_staging(nv, tx, TRUE);
} else {
if (buf->status & NOUVEAU_BUFFER_STATUS_GPU_WRITING) {
/* The GPU is currently writing to this buffer. Copy its current
* contents to a staging area in the GART. This is necessary since
* not the whole area being mapped is being discarded.
*/
if (buf->data) {
align_free(buf->data);
buf->data = NULL;
@ -364,6 +407,8 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
nouveau_transfer_staging(nv, tx, FALSE);
nouveau_transfer_read(nv, tx);
} else {
/* The buffer is currently idle. Create a staging area for writes,
* and make sure that the cached data is up-to-date. */
if (usage & PIPE_TRANSFER_WRITE)
nouveau_transfer_staging(nv, tx, TRUE);
if (!buf->data)
@ -376,6 +421,8 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
return buf->data + box->x;
}
/* At this point, buf->domain == GART */
if (nouveau_buffer_should_discard(buf, usage)) {
int ref = buf->base.reference.count - 1;
nouveau_buffer_reallocate(nv->screen, buf, buf->domain);
@ -383,6 +430,12 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
nv->invalidate_resource_storage(nv, &buf->base, ref);
}
/* Note that nouveau_bo_map ends up doing a nouveau_bo_wait with the
* relevant flags. If buf->mm is set, that means this resource is part of a
* larger slab bo that holds multiple resources. So in that case, don't
* wait on the whole slab and instead use the logic below to return a
* reasonable buffer for that case.
*/
ret = nouveau_bo_map(buf->bo,
buf->mm ? 0 : nouveau_screen_transfer_flags(usage),
nv->client);
@ -396,6 +449,10 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
if ((usage & PIPE_TRANSFER_UNSYNCHRONIZED) || !buf->mm)
return map;
/* If the GPU is currently reading/writing this buffer, we shouldn't
* interfere with its progress. So instead we either wait for the GPU to
* complete its operation, or set up a staging area to perform our work in.
*/
if (nouveau_buffer_busy(buf, usage & PIPE_TRANSFER_READ_WRITE)) {
if (unlikely(usage & PIPE_TRANSFER_DISCARD_WHOLE_RESOURCE)) {
/* Discarding was not possible, must sync because
@ -403,6 +460,8 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
nouveau_buffer_sync(buf, usage & PIPE_TRANSFER_READ_WRITE);
} else
if (usage & PIPE_TRANSFER_DISCARD_RANGE) {
/* The whole range is being discarded, so it doesn't matter what was
* there before. No need to copy anything over. */
nouveau_transfer_staging(nv, tx, TRUE);
map = tx->map;
} else
@ -412,6 +471,8 @@ nouveau_buffer_transfer_map(struct pipe_context *pipe,
else
nouveau_buffer_sync(buf, usage & PIPE_TRANSFER_READ_WRITE);
} else {
/* It is expected that the returned buffer be a representation of the
* data in question, so we must copy it over from the buffer. */
nouveau_transfer_staging(nv, tx, TRUE);
if (tx->map)
memcpy(tx->map, map, box->width);
@ -435,6 +496,12 @@ nouveau_buffer_transfer_flush_region(struct pipe_context *pipe,
nouveau_transfer_write(nouveau_context(pipe), tx, box->x, box->width);
}
/* Unmap stage of the transfer. If it was a WRITE transfer and the map that
* was returned was not the real resource's data, this needs to transfer the
* data back to the resource.
*
* Also marks vbo/cb dirty if the buffer's binding
*/
static void
nouveau_buffer_transfer_unmap(struct pipe_context *pipe,
struct pipe_transfer *transfer)

4
src/gallium/drivers/nouveau/nouveau_buffer.h
View File

@ -33,9 +33,9 @@ struct nv04_resource {
uint64_t address; /* virtual address (nv50+) */
uint8_t *data;
uint8_t *data; /* resource's contents, if domain == 0, or cached */
struct nouveau_bo *bo;
uint32_t offset;
uint32_t offset; /* offset into the data/bo */
uint8_t status;
uint8_t domain;