| Message ID | 1344958496-9373-21-git-send-email-t.stanislaws@samsung.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Tomasz, Thanks for the patch. Just a couple of small comments below. On Tuesday 14 August 2012 17:34:50 Tomasz Stanislawski wrote: > This patch adds support for exporting a dma-contig buffer using > DMABUF interface. > > Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com> > Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> > --- > drivers/media/video/videobuf2-dma-contig.c | 204 +++++++++++++++++++++++++ > 1 file changed, 204 insertions(+) > > diff --git a/drivers/media/video/videobuf2-dma-contig.c > b/drivers/media/video/videobuf2-dma-contig.c index 7fc71a0..bb2b4ac8 100644 > --- a/drivers/media/video/videobuf2-dma-contig.c > +++ b/drivers/media/video/videobuf2-dma-contig.c [snip] > +static struct sg_table *vb2_dc_dmabuf_ops_map( > + struct dma_buf_attachment *db_attach, enum dma_data_direction dir) > +{ > + struct vb2_dc_attachment *attach = db_attach->priv; > + /* stealing dmabuf mutex to serialize map/unmap operations */ Why isn't this operation serialized by the dma-buf core itself ? > + struct mutex *lock = &db_attach->dmabuf->lock; > + struct sg_table *sgt; > + int ret; > + > + mutex_lock(lock); > + > + sgt = &attach->sgt; > + /* return previously mapped sg table */ > + if (attach->dir == dir) { > + mutex_unlock(lock); > + return sgt; > + } > + > + /* release any previous cache */ > + if (attach->dir != DMA_NONE) { > + dma_unmap_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, > + attach->dir); > + attach->dir = DMA_NONE; > + } > + > + /* mapping to the client with new direction */ > + ret = dma_map_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, dir); > + if (ret <= 0) { > + pr_err("failed to map scatterlist\n"); > + mutex_unlock(lock); > + return ERR_PTR(-EIO); > + } > + > + attach->dir = dir; > + > + mutex_unlock(lock); > + > + return sgt; > +} [snip] > +static int vb2_dc_dmabuf_ops_mmap(struct dma_buf *dbuf, > + struct vm_area_struct *vma) > +{ > + /* Dummy support for mmap */ > + return -ENOTTY; What about calling the dma-contig mmap handler here ? Is there a specific reason why you haven't implemented mmap support for dmabuf ? > +} > + > +static struct dma_buf_ops vb2_dc_dmabuf_ops = { > + .attach = vb2_dc_dmabuf_ops_attach, > + .detach = vb2_dc_dmabuf_ops_detach, > + .map_dma_buf = vb2_dc_dmabuf_ops_map, > + .unmap_dma_buf = vb2_dc_dmabuf_ops_unmap, > + .kmap = vb2_dc_dmabuf_ops_kmap, > + .kmap_atomic = vb2_dc_dmabuf_ops_kmap, > + .vmap = vb2_dc_dmabuf_ops_vmap, > + .mmap = vb2_dc_dmabuf_ops_mmap, > + .release = vb2_dc_dmabuf_ops_release, > +}; > + > +static struct sg_table *vb2_dc_get_base_sgt(struct vb2_dc_buf *buf) > +{ > + int ret; > + struct sg_table *sgt; > + > + sgt = kmalloc(sizeof(*sgt), GFP_KERNEL); > + if (!sgt) { > + dev_err(buf->dev, "failed to alloc sg table\n"); > + return ERR_PTR(-ENOMEM); > + } > + > + ret = dma_get_sgtable(buf->dev, sgt, buf->vaddr, buf->dma_addr, > + buf->size); > + if (ret < 0) { > + dev_err(buf->dev, "failed to get scatterlist from DMA API\n"); > + kfree(sgt); > + return ERR_PTR(ret); > + } As this function is only used below, where the exact value of the error code is ignored, what about just returning NULL on failure ? Another option is to return the error code in vb2_dc_get_dmabuf (not sure if that would be useful though). > + > + return sgt; > +} > + > +static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv) > +{ > + struct vb2_dc_buf *buf = buf_priv; > + struct dma_buf *dbuf; > + struct sg_table *sgt = buf->sgt_base; > + > + if (!sgt) > + sgt = vb2_dc_get_base_sgt(buf); > + if (WARN_ON(IS_ERR(sgt))) > + return NULL; > + > + /* cache base sgt for future use */ > + buf->sgt_base = sgt; You can move this assignment inside the first if, there's no need to execute it every time. The WARN_ON can also be moved inside the first if, as buf- >sgt_base will either be NULL or valid. You can then get rid of the sgt variable initialization by testing if (!buf->sgt_base). > + dbuf = dma_buf_export(buf, &vb2_dc_dmabuf_ops, buf->size, 0); > + if (IS_ERR(dbuf)) > + return NULL; > + > + /* dmabuf keeps reference to vb2 buffer */ > + atomic_inc(&buf->refcount); > + > + return dbuf; > +}
Hi Laurent, Thank you for your comments. On 08/21/2012 12:03 PM, Laurent Pinchart wrote: > Hi Tomasz, > > Thanks for the patch. > > Just a couple of small comments below. > > On Tuesday 14 August 2012 17:34:50 Tomasz Stanislawski wrote: >> This patch adds support for exporting a dma-contig buffer using >> DMABUF interface. >> >> Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com> >> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> >> --- >> drivers/media/video/videobuf2-dma-contig.c | 204 +++++++++++++++++++++++++ >> 1 file changed, 204 insertions(+) >> >> diff --git a/drivers/media/video/videobuf2-dma-contig.c >> b/drivers/media/video/videobuf2-dma-contig.c index 7fc71a0..bb2b4ac8 100644 >> --- a/drivers/media/video/videobuf2-dma-contig.c >> +++ b/drivers/media/video/videobuf2-dma-contig.c > > [snip] > >> +static struct sg_table *vb2_dc_dmabuf_ops_map( >> + struct dma_buf_attachment *db_attach, enum dma_data_direction dir) >> +{ >> + struct vb2_dc_attachment *attach = db_attach->priv; >> + /* stealing dmabuf mutex to serialize map/unmap operations */ > > Why isn't this operation serialized by the dma-buf core itself ? > Indeed, it is a very good question. The lock was introduced in RFCv3 of DMABUF patches. It was dedicated to serialize attach/detach calls. No requirements for map/unmap serialization were stated so serialization was delegated to an exporter. A deadlock could occur if dma_map_attachment is called from inside of attach ops. IMO, such an operation is invalid because an attachment list is not in a valid state while attach ops is being processed. Do you think that stealing a lock from dma-buf internals is too hacky? I prefer not to introduce any extra locks in dma-contig allocator but it is not a big deal to add it. >> + struct mutex *lock = &db_attach->dmabuf->lock; >> + struct sg_table *sgt; >> + int ret; >> + >> + mutex_lock(lock); >> + >> + sgt = &attach->sgt; >> + /* return previously mapped sg table */ >> + if (attach->dir == dir) { >> + mutex_unlock(lock); >> + return sgt; >> + } >> + >> + /* release any previous cache */ >> + if (attach->dir != DMA_NONE) { >> + dma_unmap_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, >> + attach->dir); >> + attach->dir = DMA_NONE; >> + } >> + >> + /* mapping to the client with new direction */ >> + ret = dma_map_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, dir); >> + if (ret <= 0) { >> + pr_err("failed to map scatterlist\n"); >> + mutex_unlock(lock); >> + return ERR_PTR(-EIO); >> + } >> + >> + attach->dir = dir; >> + >> + mutex_unlock(lock); >> + >> + return sgt; >> +} > > [snip] > >> +static int vb2_dc_dmabuf_ops_mmap(struct dma_buf *dbuf, >> + struct vm_area_struct *vma) >> +{ >> + /* Dummy support for mmap */ >> + return -ENOTTY; > > What about calling the dma-contig mmap handler here ? Is there a specific > reason why you haven't implemented mmap support for dmabuf ? > The mmap ops is mandatory in the latest DMABUF api. I added a stub function to make DC work with DMABUF without any big effort. Calling vb2_dc_mmap from mmap ops seams to be a simple and safe way to handle mmap functionality. Thank you for spotting this :) >> +} >> + >> +static struct dma_buf_ops vb2_dc_dmabuf_ops = { >> + .attach = vb2_dc_dmabuf_ops_attach, >> + .detach = vb2_dc_dmabuf_ops_detach, >> + .map_dma_buf = vb2_dc_dmabuf_ops_map, >> + .unmap_dma_buf = vb2_dc_dmabuf_ops_unmap, >> + .kmap = vb2_dc_dmabuf_ops_kmap, >> + .kmap_atomic = vb2_dc_dmabuf_ops_kmap, >> + .vmap = vb2_dc_dmabuf_ops_vmap, >> + .mmap = vb2_dc_dmabuf_ops_mmap, >> + .release = vb2_dc_dmabuf_ops_release, >> +}; >> + >> +static struct sg_table *vb2_dc_get_base_sgt(struct vb2_dc_buf *buf) >> +{ >> + int ret; >> + struct sg_table *sgt; >> + >> + sgt = kmalloc(sizeof(*sgt), GFP_KERNEL); >> + if (!sgt) { >> + dev_err(buf->dev, "failed to alloc sg table\n"); >> + return ERR_PTR(-ENOMEM); >> + } >> + >> + ret = dma_get_sgtable(buf->dev, sgt, buf->vaddr, buf->dma_addr, >> + buf->size); >> + if (ret < 0) { >> + dev_err(buf->dev, "failed to get scatterlist from DMA API\n"); >> + kfree(sgt); >> + return ERR_PTR(ret); >> + } > > As this function is only used below, where the exact value of the error code > is ignored, what about just returning NULL on failure ? Another option is to > return the error code in vb2_dc_get_dmabuf (not sure if that would be useful > though). > >> + >> + return sgt; >> +} >> + >> +static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv) >> +{ >> + struct vb2_dc_buf *buf = buf_priv; >> + struct dma_buf *dbuf; >> + struct sg_table *sgt = buf->sgt_base; >> + >> + if (!sgt) >> + sgt = vb2_dc_get_base_sgt(buf); >> + if (WARN_ON(IS_ERR(sgt))) >> + return NULL; >> + >> + /* cache base sgt for future use */ >> + buf->sgt_base = sgt; > > You can move this assignment inside the first if, there's no need to execute > it every time. The WARN_ON can also be moved inside the first if, as buf- >> sgt_base will either be NULL or valid. You can then get rid of the sgt > variable initialization by testing if (!buf->sgt_base). I agree. I will apply this fix in v9. > >> + dbuf = dma_buf_export(buf, &vb2_dc_dmabuf_ops, buf->size, 0); >> + if (IS_ERR(dbuf)) >> + return NULL; >> + >> + /* dmabuf keeps reference to vb2 buffer */ >> + atomic_inc(&buf->refcount); >> + >> + return dbuf; >> +} > Regards, Tomasz Stanislawski
Hi Tomasz, On Tuesday 21 August 2012 15:47:13 Tomasz Stanislawski wrote: > On 08/21/2012 12:03 PM, Laurent Pinchart wrote: > > On Tuesday 14 August 2012 17:34:50 Tomasz Stanislawski wrote: > >> This patch adds support for exporting a dma-contig buffer using > >> DMABUF interface. > >> > >> Signed-off-by: Tomasz Stanislawski <t.stanislaws@samsung.com> > >> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com> > >> --- > >> > >> drivers/media/video/videobuf2-dma-contig.c | 204 ++++++++++++++++++++++ > >> 1 file changed, 204 insertions(+) > >> > >> diff --git a/drivers/media/video/videobuf2-dma-contig.c > >> b/drivers/media/video/videobuf2-dma-contig.c index 7fc71a0..bb2b4ac8 > >> 100644 > >> --- a/drivers/media/video/videobuf2-dma-contig.c > >> +++ b/drivers/media/video/videobuf2-dma-contig.c > > > > [snip] > > > >> +static struct sg_table *vb2_dc_dmabuf_ops_map( > >> + struct dma_buf_attachment *db_attach, enum dma_data_direction dir) > >> +{ > >> + struct vb2_dc_attachment *attach = db_attach->priv; > >> + /* stealing dmabuf mutex to serialize map/unmap operations */ > > > > Why isn't this operation serialized by the dma-buf core itself ? > > Indeed, it is a very good question. The lock was introduced in RFCv3 of > DMABUF patches. It was dedicated to serialize attach/detach calls. > No requirements for map/unmap serialization were stated so serialization > was delegated to an exporter. > > A deadlock could occur if dma_map_attachment is called from inside > of attach ops. IMO, such an operation is invalid because an attachment > list is not in a valid state while attach ops is being processed. > > Do you think that stealing a lock from dma-buf internals is too hacky? No, I would be OK with that, but I'd like to make sure that it won't bite us back later. If there's a specific reason why the lock is not taken by the dmabuf core around map/unmap calls, stealing the same lock might cause unforeseen problems. That's why I would like to understand why the core doesn't perform locking on its own. > I prefer not to introduce any extra locks in dma-contig allocator Agreed. > but it is not a big deal to add it. > > >> + struct mutex *lock = &db_attach->dmabuf->lock; > >> + struct sg_table *sgt; > >> + int ret; > >> + > >> + mutex_lock(lock); > >> + > >> + sgt = &attach->sgt; > >> + /* return previously mapped sg table */ > >> + if (attach->dir == dir) { > >> + mutex_unlock(lock); > >> + return sgt; > >> + } > >> + > >> + /* release any previous cache */ > >> + if (attach->dir != DMA_NONE) { > >> + dma_unmap_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, > >> + attach->dir); > >> + attach->dir = DMA_NONE; > >> + } > >> + > >> + /* mapping to the client with new direction */ > >> + ret = dma_map_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, dir); > >> + if (ret <= 0) { > >> + pr_err("failed to map scatterlist\n"); > >> + mutex_unlock(lock); > >> + return ERR_PTR(-EIO); > >> + } > >> + > >> + attach->dir = dir; > >> + > >> + mutex_unlock(lock); > >> + > >> + return sgt; > >> +}
diff --git a/drivers/media/video/videobuf2-dma-contig.c b/drivers/media/video/videobuf2-dma-contig.c index 7fc71a0..bb2b4ac8 100644 --- a/drivers/media/video/videobuf2-dma-contig.c +++ b/drivers/media/video/videobuf2-dma-contig.c @@ -36,6 +36,7 @@ struct vb2_dc_buf { /* MMAP related */ struct vb2_vmarea_handler handler; atomic_t refcount; + struct sg_table *sgt_base; /* USERPTR related */ struct vm_area_struct *vma; @@ -142,6 +143,10 @@ static void vb2_dc_put(void *buf_priv) if (!atomic_dec_and_test(&buf->refcount)) return; + if (buf->sgt_base) { + sg_free_table(buf->sgt_base); + kfree(buf->sgt_base); + } dma_free_coherent(buf->dev, buf->size, buf->vaddr, buf->dma_addr); kfree(buf); } @@ -213,6 +218,204 @@ static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma) } /*********************************************/ +/* DMABUF ops for exporters */ +/*********************************************/ + +struct vb2_dc_attachment { + struct sg_table sgt; + enum dma_data_direction dir; +}; + +static int vb2_dc_dmabuf_ops_attach(struct dma_buf *dbuf, struct device *dev, + struct dma_buf_attachment *dbuf_attach) +{ + struct vb2_dc_attachment *attach; + unsigned int i; + struct scatterlist *rd, *wr; + struct sg_table *sgt; + struct vb2_dc_buf *buf = dbuf->priv; + int ret; + + attach = kzalloc(sizeof(*attach), GFP_KERNEL); + if (!attach) + return -ENOMEM; + + sgt = &attach->sgt; + /* Copy the buf->base_sgt scatter list to the attachment, as we can't + * map the same scatter list to multiple attachments at the same time. + */ + ret = sg_alloc_table(sgt, buf->sgt_base->orig_nents, GFP_KERNEL); + if (ret) { + kfree(attach); + return -ENOMEM; + } + + rd = buf->sgt_base->sgl; + wr = sgt->sgl; + for (i = 0; i < sgt->orig_nents; ++i) { + sg_set_page(wr, sg_page(rd), rd->length, rd->offset); + rd = sg_next(rd); + wr = sg_next(wr); + } + + attach->dir = DMA_NONE; + dbuf_attach->priv = attach; + + return 0; +} + +static void vb2_dc_dmabuf_ops_detach(struct dma_buf *dbuf, + struct dma_buf_attachment *db_attach) +{ + struct vb2_dc_attachment *attach = db_attach->priv; + struct sg_table *sgt; + + if (!attach) + return; + + sgt = &attach->sgt; + + /* release the scatterlist cache */ + if (attach->dir != DMA_NONE) + dma_unmap_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, + attach->dir); + sg_free_table(sgt); + kfree(attach); + db_attach->priv = NULL; +} + +static struct sg_table *vb2_dc_dmabuf_ops_map( + struct dma_buf_attachment *db_attach, enum dma_data_direction dir) +{ + struct vb2_dc_attachment *attach = db_attach->priv; + /* stealing dmabuf mutex to serialize map/unmap operations */ + struct mutex *lock = &db_attach->dmabuf->lock; + struct sg_table *sgt; + int ret; + + mutex_lock(lock); + + sgt = &attach->sgt; + /* return previously mapped sg table */ + if (attach->dir == dir) { + mutex_unlock(lock); + return sgt; + } + + /* release any previous cache */ + if (attach->dir != DMA_NONE) { + dma_unmap_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, + attach->dir); + attach->dir = DMA_NONE; + } + + /* mapping to the client with new direction */ + ret = dma_map_sg(db_attach->dev, sgt->sgl, sgt->orig_nents, dir); + if (ret <= 0) { + pr_err("failed to map scatterlist\n"); + mutex_unlock(lock); + return ERR_PTR(-EIO); + } + + attach->dir = dir; + + mutex_unlock(lock); + + return sgt; +} + +static void vb2_dc_dmabuf_ops_unmap(struct dma_buf_attachment *db_attach, + struct sg_table *sgt, enum dma_data_direction dir) +{ + /* nothing to be done here */ +} + +static void vb2_dc_dmabuf_ops_release(struct dma_buf *dbuf) +{ + /* drop reference obtained in vb2_dc_get_dmabuf */ + vb2_dc_put(dbuf->priv); +} + +static void *vb2_dc_dmabuf_ops_kmap(struct dma_buf *dbuf, unsigned long pgnum) +{ + struct vb2_dc_buf *buf = dbuf->priv; + + return buf->vaddr + pgnum * PAGE_SIZE; +} + +static void *vb2_dc_dmabuf_ops_vmap(struct dma_buf *dbuf) +{ + struct vb2_dc_buf *buf = dbuf->priv; + + return buf->vaddr; +} + +static int vb2_dc_dmabuf_ops_mmap(struct dma_buf *dbuf, + struct vm_area_struct *vma) +{ + /* Dummy support for mmap */ + return -ENOTTY; +} + +static struct dma_buf_ops vb2_dc_dmabuf_ops = { + .attach = vb2_dc_dmabuf_ops_attach, + .detach = vb2_dc_dmabuf_ops_detach, + .map_dma_buf = vb2_dc_dmabuf_ops_map, + .unmap_dma_buf = vb2_dc_dmabuf_ops_unmap, + .kmap = vb2_dc_dmabuf_ops_kmap, + .kmap_atomic = vb2_dc_dmabuf_ops_kmap, + .vmap = vb2_dc_dmabuf_ops_vmap, + .mmap = vb2_dc_dmabuf_ops_mmap, + .release = vb2_dc_dmabuf_ops_release, +}; + +static struct sg_table *vb2_dc_get_base_sgt(struct vb2_dc_buf *buf) +{ + int ret; + struct sg_table *sgt; + + sgt = kmalloc(sizeof(*sgt), GFP_KERNEL); + if (!sgt) { + dev_err(buf->dev, "failed to alloc sg table\n"); + return ERR_PTR(-ENOMEM); + } + + ret = dma_get_sgtable(buf->dev, sgt, buf->vaddr, buf->dma_addr, + buf->size); + if (ret < 0) { + dev_err(buf->dev, "failed to get scatterlist from DMA API\n"); + kfree(sgt); + return ERR_PTR(ret); + } + + return sgt; +} + +static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv) +{ + struct vb2_dc_buf *buf = buf_priv; + struct dma_buf *dbuf; + struct sg_table *sgt = buf->sgt_base; + + if (!sgt) + sgt = vb2_dc_get_base_sgt(buf); + if (WARN_ON(IS_ERR(sgt))) + return NULL; + + /* cache base sgt for future use */ + buf->sgt_base = sgt; + + dbuf = dma_buf_export(buf, &vb2_dc_dmabuf_ops, buf->size, 0); + if (IS_ERR(dbuf)) + return NULL; + + /* dmabuf keeps reference to vb2 buffer */ + atomic_inc(&buf->refcount); + + return dbuf; +} + +/*********************************************/ /* callbacks for USERPTR buffers */ /*********************************************/ @@ -519,6 +722,7 @@ static void *vb2_dc_attach_dmabuf(void *alloc_ctx, struct dma_buf *dbuf, const struct vb2_mem_ops vb2_dma_contig_memops = { .alloc = vb2_dc_alloc, .put = vb2_dc_put, + .get_dmabuf = vb2_dc_get_dmabuf, .cookie = vb2_dc_cookie, .vaddr = vb2_dc_vaddr, .mmap = vb2_dc_mmap,