[PATCH v2 1/3] spi: implemented driver for Cirrus EP93xx SPI controller

[Mika Westerberg]

On Thu, Apr 01, 2010 at 01:15:20AM +0100, Martin Guy wrote:
> On 3/25/10, Mika Westerberg <mika.westerberg at iki.fi> wrote:
> >  > > This patch adds an SPI master driver for the Cirrus EP93xx SPI controller found
> >  > >  in EP93xx chips (EP9301, EP9302, EP9307, EP9312 and EP9315).
> >  > >
> >  > >  Driver currently supports only interrupt driven mode but in future we may add
> >  > >  polling mode support as well.
> 
> I've been staring more at this again and it looks (2 clock
> strangenesses and extensive control reg setting apart) like good code.
> I have another question: like the Cirrus driver, this takes 100% CPU
> doing busy wait for the current transfer to complete.

Hi,

I tried to find out whether the driver did something wrong to get
into busylooping but couldn't find anything. In case of MMC/SD
cards, through mmc_spi, transfer sizes are >= 512 bytes at a time
and FIFO size is only 8 bytes (or words) so the CPU is expected to
be pretty busy serving interrupts from the SSP.

I'm about to post updated series with your comments addressed. I
also added support for polling transfers.

> Given that this driver is interrupt-based, is there any reason why it
> can't do something else in the meanwhile?
> Not that that's a reason not to include it in 2.6.35 - it works well
> and we can think whether to make it more efficient in N+1...