Re: [PATCH v5] serial: spi: add spi-uart driver for Maxim 3110

[Feng Tang <feng.tang@intel.com>]

On Wed, 3 Mar 2010 12:51:58 +0800
David Brownell <david-b@pacbell.net> wrote:

> On Tuesday 02 March 2010, Feng Tang wrote:
> > + * 3. This driver doesn't support work with a spi cotnroller in
> > DMA mode, 
> 
> As Grant said:  That's a bug ... one that will randomly
> kick in based on whether the underlying SPI controller driver
> happens to use DMA for a given transaction.
> 
> 
>From this perspective, yes, it's a bug that this driver use non DMA-safe
IO buffer, which prevents it to be portable for all kinds of controllers,
and I can make it DMA safe. 

But I still don't think it's a good idea to use DMA for Max3110 for
performance reason, I know there is some spi controller who only works in
DMA mode. 

Here comes another idea, can we add a capability flag in struct spi_master
indicating the master supporting poll or dma or both. Also we add similar
bits in struct spi_transfer indicating the this transfer wants to be handled
in poll or dma mode. For spi controller driver, it can claim its
capability when registering as a spi_master, for a spi device driver, it can
select the working mode based on spi_master's capability and set the working
mode in struct spi_transfer. Then controller and device don't need to guess
what the other is capable, and make the info public. Any thoughts?

Thanks,
Feng