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    SubjectRe: [PATCH] firewire: fw-ohci: sync AT dma buffer before use
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    On Wed, 2008-03-12 at 17:43 -0400, Jarod Wilson wrote:
    > diff --git a/drivers/firewire/fw-ohci.c b/drivers/firewire/fw-ohci.c
    > index 081a434..fc45868 100644
    > --- a/drivers/firewire/fw-ohci.c
    > +++ b/drivers/firewire/fw-ohci.c
    > @@ -780,6 +780,10 @@ at_context_queue_packet(struct context *ctx, struct fw_packet *packet)
    >
    > context_append(ctx, d, z, 4 - z);
    >
    > + /* Sync the DMA buffer up for the device to read from */
    > + dma_sync_single_for_device(ohci->card.device, payload_bus,
    > + packet->payload_length, DMA_TO_DEVICE);
    > +
    > /* If the context isn't already running, start it up. */
    > reg = reg_read(ctx->ohci, CONTROL_SET(ctx->regs));
    > if ((reg & CONTEXT_RUN) == 0)
    >

    Two things:

    1. The dma_sync should probably be done before the context_append
    because the controller could in theory start reading the data as soon as
    context_append is called right?

    2. As an optimization, we should attempt to allocate the payload in the
    lower 32-bits of physical memory, to prevent extra memcopies on x86_64.
    I think this can be done by adding GFP_DMA32 to kmalloc where the
    payload was allocated in fw-cdev.c. There might be other places where
    we would benefit from GFP_DMA32 also. Of course, these optimizations
    are probably better saved for another patch.

    -David



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