Re: [PATCH 01/16] Blackfin SPI Driver: ensure cache coherency before doing DMA

Mike Frysinger
2008-11-20T21:01:37Z

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));
>
> Could you explain why you're not using dma_map_*() calls
> or the rx_dma (and tx_dma) addresses the caller may pass?

i'm not familiar with said API. i worked with what was there already.

> 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 ?

> 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.
-mike