Re: Spinlock vs mutexes for spi network driver

[Amit Uttamchandani <amit.uttam-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Thu, Mar 18, 2010 at 06:11:00PM -0400, Ned Forrester wrote:

[...]

> 
> I'm not familiar with spi_read and spi_write.  I guess those may be part
> of the user space driver: spidev?  (I wrote a dedicated protocol driver
> for my device.)

Looking at spi.c, spi_read and spi_write both use spi_sync, so both are
blocking.

> 
> It could be a lot of places, from bug in your code to bug in the
> controller driver.  I'm not sure how much testing omap2_mcspi.c has
> received.  When I first started using pxa2xx_spi.c, less than a year
> after it appeared in the kernel, I found a variety of bugs.  I then
> spent about 6 months re-writing the driver to handle a high data-rate
> read-only master.  It was much harder for me than I expected.

You're right. In our case, a lot of the problems where from the FPGA
side of things. We implemented the open cores ethmac controller in our
FPGA. Then wrote a SPI to wishbone protocol communication controller. I
am sure there are bugs in there too.

> 
> > Could I be using SPI with dma to improve speed and maybe have access to
> > more resource in system memory?
> 
> Way too short a question, with way too many unspecified variables.  I
> really can't help you with that, because I know nothing about omap.  DMA
> is useful if you are transmitting/receiving lots of data.  If your
> device requires short exchanges (bytes, not Kbytes or Mbytes) with
> decision making in between, then DMA might not help.  Many of the
> controller drivers have DMA built-in, and it is not hard to enable it,
> but I don't know about omap2_mcspi.c.
> 

I guess I won't be needing DMA as our transfers and quite small. Thanks
for the explanation.

Thank you again for your help.

Amit


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