lkml.org 
[lkml]   [2020]   [May]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v5 29/38] drm: rcar-du: fix common struct sg_table related issues
    Hi Marek,

    Thank you for the patch.

    On Wed, May 13, 2020 at 03:32:36PM +0200, Marek Szyprowski wrote:
    > The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
    > returns the number of the created entries in the DMA address space.
    > However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
    > dma_unmap_sg must be called with the original number of the entries
    > passed to the dma_map_sg().
    >
    > struct sg_table is a common structure used for describing a non-contiguous
    > memory buffer, used commonly in the DRM and graphics subsystems. It
    > consists of a scatterlist with memory pages and DMA addresses (sgl entry),
    > as well as the number of scatterlist entries: CPU pages (orig_nents entry)
    > and DMA mapped pages (nents entry).
    >
    > It turned out that it was a common mistake to misuse nents and orig_nents
    > entries, calling DMA-mapping functions with a wrong number of entries or
    > ignoring the number of mapped entries returned by the dma_map_sg()
    > function.
    >
    > To avoid such issues, lets use a common dma-mapping wrappers operating
    > directly on the struct sg_table objects and use scatterlist page
    > iterators where possible. This, almost always, hides references to the
    > nents and orig_nents entries, making the code robust, easier to follow
    > and copy/paste safe.
    >
    > dma_map_sgtable() function returns zero or an error code, so adjust the
    > return value check for the vsp1_du_map_sg() function.
    >
    > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

    This is a very nice simplification, I've always foudn the dma_map_sg API
    cumbersome to use.

    Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

    I assume you will get the whole series merged in one go. If I need to
    pick the patch up at any point, please let me know. Otherwise I'll wait
    until I see it upstream, no reply needed :-)

    > ---
    > For more information, see '[PATCH v5 00/38] DRM: fix struct sg_table nents
    > vs. orig_nents misuse' thread:
    > https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/
    > ---
    > drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 3 +--
    > drivers/media/platform/vsp1/vsp1_drm.c | 8 ++++----
    > 2 files changed, 5 insertions(+), 6 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
    > index 5e4faf2..2fc1816 100644
    > --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
    > +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
    > @@ -197,9 +197,8 @@ int rcar_du_vsp_map_fb(struct rcar_du_vsp *vsp, struct drm_framebuffer *fb,
    > goto fail;
    >
    > ret = vsp1_du_map_sg(vsp->vsp, sgt);
    > - if (!ret) {
    > + if (ret) {
    > sg_free_table(sgt);
    > - ret = -ENOMEM;
    > goto fail;
    > }
    > }
    > diff --git a/drivers/media/platform/vsp1/vsp1_drm.c b/drivers/media/platform/vsp1/vsp1_drm.c
    > index a4a45d6..86d5e3f 100644
    > --- a/drivers/media/platform/vsp1/vsp1_drm.c
    > +++ b/drivers/media/platform/vsp1/vsp1_drm.c
    > @@ -912,8 +912,8 @@ int vsp1_du_map_sg(struct device *dev, struct sg_table *sgt)
    > * skip cache sync. This will need to be revisited when support for
    > * non-coherent buffers will be added to the DU driver.
    > */
    > - return dma_map_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
    > - DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
    > + return dma_map_sgtable(vsp1->bus_master, sgt, DMA_TO_DEVICE,
    > + DMA_ATTR_SKIP_CPU_SYNC);
    > }
    > EXPORT_SYMBOL_GPL(vsp1_du_map_sg);
    >
    > @@ -921,8 +921,8 @@ void vsp1_du_unmap_sg(struct device *dev, struct sg_table *sgt)
    > {
    > struct vsp1_device *vsp1 = dev_get_drvdata(dev);
    >
    > - dma_unmap_sg_attrs(vsp1->bus_master, sgt->sgl, sgt->nents,
    > - DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
    > + dma_unmap_sgtable(vsp1->bus_master, sgt, DMA_TO_DEVICE,
    > + DMA_ATTR_SKIP_CPU_SYNC);
    > }
    > EXPORT_SYMBOL_GPL(vsp1_du_unmap_sg);
    >

    --
    Regards,

    Laurent Pinchart

    \
     
     \ /
      Last update: 2020-05-13 16:23    [W:4.034 / U:0.024 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site