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    SubjectRe: [PATCH 01/16] Blackfin SPI Driver: ensure cache coherency before doing DMA
    On Thu, Nov 20, 2008 at 16:47, David Brownell wrote:
    > On Thursday 20 November 2008, Mike Frysinger wrote:
    >> On Thu, Nov 20, 2008 at 15:24, David Brownell wrote:
    >> > On Monday 17 November 2008, Bryan Wu wrote:
    >> >> /* set transfer mode, and enable SPI */
    >> >> dev_dbg(&drv_data->pdev->dev, "doing DMA in.\n");
    >> >>
    >> >> + /* invalidate caches, if needed */
    >> >> + if (bfin_addr_dcachable((unsigned long) drv_data->rx))
    >> >> + invalidate_dcache_range((unsigned long) drv_data->rx,
    >> >> + (unsigned long) (drv_data->rx +
    >> >> + drv_data->len));
    >> >
    >> > As a rule, you should use the standard kernel interfaces
    >> > for such stuff instead of platform-specific calls like
    >> > those two. There are a LOT more developers who can find
    >> > and fix bugs that way.
    >>
    >> could you elaborate on the common calls that would replace these ?
    >
    > See Documentation/DMA-(mapping,API}.txt ... the "mapping"
    > document's section on what memory may be used for DMA is
    > not otherwise replicated in the description of the "generic"
    > versions of those API calls.
    >
    > Basically, dma_map_single(), dma_unmap_single() ... and
    > remember that the caller may have done the mappings for
    > you already.

    these arent required to provide coherent memory right ? if that's the
    case, i can take a look at getting things updated.

    >> > Also, this patch affects the "not full duplex" branch of
    >> > this routine. DMA here seems unusually convoluted ... but
    >> > if you didn't invalidate the cache (RX path) before
    >> > flushing it (TX path) and instead did it the other way
    >> > aroound, would you actually *need* separate branches?
    >>
    >> it's convoluted because the hardware sucks. it cant do full duplex
    >> with DMA. full duplex only works in the non-DMA case.
    >
    > Ah, ok. Sucky hardware -- been there, done that, still doing. ;)
    >
    > It'd be nice if one of patches snuck in a comment on that
    > point: "Full duplex only works for non-DMA transfers."
    > Same rationale: you may know this hardware inside out,
    > but the next person won't.

    well, hopefully if they dont know they wont be touching the driver ;).
    i'll add a comment in this code chunk. thanks for the feedback.
    -mike


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