[PATCH 1/2] dma-buf: start caching of sg_table objects v2
Christian König
ckoenig.leichtzumerken at gmail.com
Wed May 15 09:25:01 UTC 2019
Am 15.05.19 um 10:58 schrieb Daniel Vetter:
> On Tue, May 14, 2019 at 04:05:14PM +0200, Christian König wrote:
>> To allow a smooth transition from pinning buffer objects to dynamic
>> invalidation we first start to cache the sg_table for an attachment.
>>
>> v2: keep closer to the DRM implementation
>>
>> Signed-off-by: Christian König <christian.koenig at amd.com>
> i915 doesn't use the prime helpers, so this would be a change for us.
Not a problem at all, see below. I've added an cache_sgt_mapping member
into the dma_buf_ops structure. Only when this member is true the
functionality is enabled.
So I'm just moving code around in those two patches and no functional
change at all.
Regards,
Christian.
> Not
> sure that matters. Since we can't use this as an easy way out of the
> locking problem around reservation_object I'm not sure how useful it is to
> move this ahead. At least until we have a clearer picture on how we plan
> to roll out the dynamic dma-buf stuff. Once we have a bit more clarity
> there I'm all for merging prep work, but as-is I'd be cautious ... This
> stuff is a lot more tricky than it seems at first :-/
> -Daniel
>> ---
>> drivers/dma-buf/dma-buf.c | 27 +++++++++++++++++++++++++--
>> include/linux/dma-buf.h | 13 +++++++++++++
>> 2 files changed, 38 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
>> index 7c858020d14b..a2d34c6b80a5 100644
>> --- a/drivers/dma-buf/dma-buf.c
>> +++ b/drivers/dma-buf/dma-buf.c
>> @@ -573,6 +573,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>> list_add(&attach->node, &dmabuf->attachments);
>>
>> mutex_unlock(&dmabuf->lock);
>> +
>> return attach;
>>
>> err_attach:
>> @@ -595,6 +596,9 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>> if (WARN_ON(!dmabuf || !attach))
>> return;
>>
>> + if (attach->sgt)
>> + dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
>> +
>> mutex_lock(&dmabuf->lock);
>> list_del(&attach->node);
>> if (dmabuf->ops->detach)
>> @@ -630,10 +634,27 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>> if (WARN_ON(!attach || !attach->dmabuf))
>> return ERR_PTR(-EINVAL);
>>
>> + if (attach->sgt) {
>> + /*
>> + * Two mappings with different directions for the same
>> + * attachment are not allowed.
>> + */
>> + if (attach->dir != direction &&
>> + attach->dir != DMA_BIDIRECTIONAL)
>> + return ERR_PTR(-EBUSY);
>> +
>> + return attach->sgt;
>> + }
>> +
>> sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
>> if (!sg_table)
>> sg_table = ERR_PTR(-ENOMEM);
>>
>> + if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
>> + attach->sgt = sg_table;
>> + attach->dir = direction;
>> + }
>> +
>> return sg_table;
>> }
>> EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
>> @@ -657,8 +678,10 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>> if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
>> return;
>>
>> - attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
>> - direction);
>> + if (attach->sgt == sg_table)
>> + return;
>> +
>> + attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
>> }
>> EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>>
>> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
>> index 58725f890b5b..45b9767e67ec 100644
>> --- a/include/linux/dma-buf.h
>> +++ b/include/linux/dma-buf.h
>> @@ -51,6 +51,15 @@ struct dma_buf_attachment;
>> * @vunmap: [optional] unmaps a vmap from the buffer
>> */
>> struct dma_buf_ops {
>> + /**
>> + * @cache_sgt_mapping:
>> + *
>> + * If true the framework will cache the first mapping made for each
>> + * attachment. This avoids creating mappings for attachments multiple
>> + * times.
>> + */
>> + bool cache_sgt_mapping;
>> +
>> /**
>> * @attach:
>> *
>> @@ -307,6 +316,8 @@ struct dma_buf {
>> * @dmabuf: buffer for this attachment.
>> * @dev: device attached to the buffer.
>> * @node: list of dma_buf_attachment.
>> + * @sgt: cached mapping.
>> + * @dir: direction of cached mapping.
>> * @priv: exporter specific attachment data.
>> *
>> * This structure holds the attachment information between the dma_buf buffer
>> @@ -322,6 +333,8 @@ struct dma_buf_attachment {
>> struct dma_buf *dmabuf;
>> struct device *dev;
>> struct list_head node;
>> + struct sg_table *sgt;
>> + enum dma_data_direction dir;
>> void *priv;
>> };
>>
>> --
>> 2.17.1
>>
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