[U-Boot] [PATCH 2/2] EXYNOS: SPI: Support SPI_PREAMBLE mode

[Vadim Bendebury]

On Mon, May 6, 2013 at 7:37 AM, Simon Glass <sjg at chromium.org> wrote:
>
> HI Vadim,
>
> On Thu, May 2, 2013 at 11:12 PM, Vadim Bendebury <vbendeb at chromium.org> wrote:
> > [the original patch removed, re-sending from a registered address]
> >
> > So, I spent some more time debugging a system which requires this
> > patch: a system, where on a SPI interface a response to a command
> > could come way later then the command data transmission completes.
> >
> > The original patch was trying to address many corner cases, but come
> > to think of it, in this situation the slave does not care about extra
> > data sent on the transmit interface, as otherwise there is no clock
> > and no data could be transferred from the slave.
> >
> > Then, for this SPI interface we do not need to set the counter of
> > clocks, and do not need to keep adding more clocks if the data has not
> > been received yet, the clocks could be just free running. And then the
> > patch becomes much simpler, what do you think:
>
> Does this deal with the performance problems that the old driver code
> had? There were a number of other patches sent upstream by Rajeshwari
> also. I wonder if it might be easier to do your improvement as a
> separate patch on top of those instead. Then it can be considered on
> its merits.
>

Hi Simon,

what performance problems are there? Do you mean that u-boot is not
fast enough when polling the SPI interface? I thought about this -
even when clocking at 50MHz (resulting in 6.125 MB/s transfer rate)
with 64 byte FIFOs there should be no problem when serving the
interface, especially when receive and transmit flows are split in
time.

Have there been any evidence of performance problems?  Also, I noticed
that the driver does not pay any respect to error conditions. I am
planning to add error monitoring/processing code, as this would be a
good way to know if there indeed are performance problems.

cheers, --vb


> Regards,
> Simon