On 6/4/26 02:42, Bobby Eshleman wrote: > From: Bobby Eshleman <[email protected]> > > get_sg_table() emitted one PAGE_SIZE sg entry per page even when the > underlying folio was larger. > > Instead, walk folios[] and emit one sg entry per folio. When folios > represent large pages (as is for MFD_HUGETLB), each sg entry is a large > page. Normal PAGE_SIZE sg tables are unchanged. > > Required by net/core/devmem to support rx-buf-size > PAGE_SIZE with > udmabuf.
That doesn't explain why this is required. Please note that accessing the pages/folio of an sg-table returned by DMA-buf is illegal and strictly forbidden! Regards, Christian. > Signed-off-by: Bobby Eshleman <[email protected]> > --- > drivers/dma-buf/udmabuf.c | 47 > ++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 42 insertions(+), 5 deletions(-) > > diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c > index 94b8ecb892bb..f28dd3788ada 100644 > --- a/drivers/dma-buf/udmabuf.c > +++ b/drivers/dma-buf/udmabuf.c > @@ -141,26 +141,63 @@ static void vunmap_udmabuf(struct dma_buf *buf, struct > iosys_map *map) > vm_unmap_ram(map->vaddr, ubuf->pagecount); > } > > +/* Return the number of contiguous pages backed by the folio at @i. > + * A udmabuf may map only part of a folio, or reference the same folio > + * in multiple non-contiguous runs, so folio_nr_pages() can't be used. > + */ > +static pgoff_t udmabuf_folio_nr_pages(struct udmabuf *ubuf, pgoff_t i) > +{ > + struct folio *f = ubuf->folios[i]; > + pgoff_t j; > + > + for (j = 1; i + j < ubuf->pagecount; j++) { > + if (ubuf->folios[i + j] != f) > + break; > + /* Same folio, but not a sequential offset within it. */ > + if (ubuf->offsets[i + j] != ubuf->offsets[i] + j * PAGE_SIZE) > + break; > + } > + return j; > +} > + > +/* Count the contiguous folio runs in @ubuf, one sg entry per run. */ > +static unsigned int udmabuf_sg_nents(struct udmabuf *ubuf) > +{ > + unsigned int nents = 0; > + pgoff_t i; > + > + for (i = 0; i < ubuf->pagecount; i += udmabuf_folio_nr_pages(ubuf, i)) > + nents++; > + return nents; > +} > + > static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf, > enum dma_data_direction direction) > { > struct udmabuf *ubuf = buf->priv; > - struct sg_table *sg; > struct scatterlist *sgl; > - unsigned int i = 0; > + struct sg_table *sg; > + pgoff_t i, run; > + unsigned int nents; > int ret; > > + nents = udmabuf_sg_nents(ubuf); > + > sg = kzalloc_obj(*sg); > if (!sg) > return ERR_PTR(-ENOMEM); > > - ret = sg_alloc_table(sg, ubuf->pagecount, GFP_KERNEL); > + ret = sg_alloc_table(sg, nents, GFP_KERNEL); > if (ret < 0) > goto err_alloc; > > - for_each_sg(sg->sgl, sgl, ubuf->pagecount, i) > - sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE, > + sgl = sg->sgl; > + for (i = 0; i < ubuf->pagecount; i += run) { > + run = udmabuf_folio_nr_pages(ubuf, i); > + sg_set_folio(sgl, ubuf->folios[i], run << PAGE_SHIFT, > ubuf->offsets[i]); > + sgl = sg_next(sgl); > + } > > ret = dma_map_sgtable(dev, sg, direction, 0); > if (ret < 0) > > -- > 2.53.0-Meta >
