Messages in this thread | | | Date | Thu, 20 Nov 2008 16:57:12 -0500 | From | "Mike Frysinger" <> | Subject | Re: [PATCH 01/16] Blackfin SPI Driver: ensure cache coherency before doing DMA |
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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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