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    SubjectRe: [PATCH 1/5] ARM: add PrimeCell generic DMA to PL022 v9
    On Mon, Aug 16, 2010 at 10:48:34PM -0600, Grant Likely wrote:
    > > + /* Map DMA buffers */
    > > + sglen = dma_map_sg(&pl022->adev->dev, pl022->sgt_rx.sgl,
    > > + pl022->sgt_rx.nents, DMA_FROM_DEVICE);
    > > + if (sglen != pages)
    > > + goto err_rx_sgmap;
    > > +
    > > + sglen = dma_map_sg(&pl022->adev->dev, pl022->sgt_tx.sgl,
    > > + pl022->sgt_tx.nents, DMA_TO_DEVICE);
    > > + if (sglen != pages)
    > > + goto err_tx_sgmap;
    > > +
    > > + /* Synchronize the TX scatterlist, invalidate buffers, caches etc */
    > > + dma_sync_sg_for_device(&pl022->adev->dev,
    > > + pl022->sgt_tx.sgl,
    > > + pl022->sgt_tx.nents,
    > > + DMA_TO_DEVICE);

    This is wrong. Mapping a scatterlist already makes it available for
    the device to use. There's no point re-doing that work by using
    the sync API.

    Let's go over the DMA API one more time.

    CPU owns buffer, device must not access

    dma_map_xx buffer ownership transitions from CPU to device

    device owns buffer, CPU must not access

    dma_sync_xx_for_cpu buffer ownership transitions from device to CPU

    CPU owns buffer, device must not access

    dma_sync_xx_for_device buffer ownership transitions from CPU to device

    device owns buffer, CPU must not access

    dma_unmap_xx buffer ownership transitions from device to CPU

    CPU owns buffer, device must not access


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      Last update: 2010-08-17 10:59    [W:0.022 / U:124.440 seconds]
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