Re: [PATCH v1 0/2] spi: dw-mid: fix simplex DMA transfers

[Andy Shevchenko <andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>]

On Wed, 2014-10-29 at 11:17 +0000, Mark Brown wrote:
> On Wed, Oct 29, 2014 at 12:37:56PM +0200, Andy Shevchenko wrote:
> > On Tue, 2014-10-28 at 22:41 +0000, Mark Brown wrote:
> 
> > >   Can you please also send a patch for Linus
> > > setting SPI_MASTER_MUST_RX and SPI_MASTER_MUST_TX - this is a bug which
> > > should be fixed in mainline but these seem a bit big for merge right
> > > now, those flags will cause the core to always ensure that both
> > > directions have data avoiding the issue?
> 
> > I'm sorry I didn't quite understand that bug.
> 
> > When those bits are set the core will always provide valid tx_buf and
> > rx_buf pointers. How would it help us? Currently driver relies on tx_dma
> > and rx_dma which are provided by clients if I understood correctly.
> 
> Uh, are you sure

There is a function in spi-dw.c called map_dma_buffers() which uses
tx_dma and rx_dma pointers. I don't see where they are initialized.

>  - how exactly has this been tested?  

I don't know how it was tested before, but, besides intel-mid-dma is
somehow broken (I won't spend time to patch it), I'm using patch I
already published which converts driver to use dw_dmac driver. With it I
run tests on a loop back.

> tx_dma and rx_dma
> *can* be provided by users but vanishingly few actually do so.  Drivers
> must not rely on the caller doing this, the feature will be going away
> apart from anything else.  If the driver is relying on this it probably
> needs to have the DMA support that's there removed as a fix and should
> be converted to use the core DMA mapping functionality in -next.

So, regarding to above what would you like me to do as next step?

-- 
Andy Shevchenko <andriy.shevchenko-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Intel Finland Oy

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