[PATCH v4] powerpc/5200: Add mpc5200-spi (non-PSC) device driver

[Grant Likely]

On Tue, Jun 23, 2009 at 8:40 AM, Kári Davíðsson<kari.davidsson at marel.com> wrote:
> Hi,
>
> I have been testing this driver a little bit (on 2.6.29.3)
>
> What happens for me is that the driver starves the system while sending
> data over the SPI interface.
>
> I think the problem is in the function (interrupt handler)
> mpc52xx_spi_irq() that calls the function mpc52xx_spi_fsm_process()
> which again is an loop that iterates over the whole data to be sent.

Hmmm, the state machine is supposed to yield after each byte sent, but
on fast transfers I could see it becoming ready to run again
immediately.

Unfortunately it is not an easy problem.  The SPI device can only
handle 1 byte at a time.  Maybe it would be better for CPU fairness if
all the work was done in a thread.  I didn't originally because I
didn't want to introduce a huge amount of scheduling overhead every
time a byte was transfered, and I wanted to keep transfers fast.  I
need to think about this some more.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.