Accessing flash directly from User Space

[Jonathan Haws]

> On Tue, 2009-10-27 at 16:52 -0600, Jonathan Haws wrote:
> > > Jonathan Haws wrote:
> > > > I had thought about using MTD, but decided against it because
> with
> > > > previous benchmarking that we did with MTD and our custom
> driver,
> > > we
> > > > found that our custom driver was about 10x faster.
> > >
> > > Ouch.  Any idea where the slowdown is coming from?
> >
> > From what I remember (I would have to dig up notes to make sure)
> it is something to do with MTD looking for a signal to go high that
> is processed a bunch before MTD even sees it.  Our flash produces a
> hardware ready signal that we are triggering off of to move on.  MTD
> took much longer to report to us that the hardware was ready.
> >
> > Thanks
> >
> 
> It would be interesting to know in more detail what is was. If we
> have a
> 10x performance increase hiding from for us I would be very
> interested
> in knowing where it is.
> 
> Are you using some custom command to the flash that the generic chip
> drivers in Linux is not yet supporting ?

Looking through our notes and talking with the engineer who was performing the tests, it was exactly that - MTD was waiting for a signal that was produced differently than the hardware ready signal.  By simply polling the flash until the hardware ready signal toggled we were able to get a much faster read and write speed.  Granted, most of our signals are being sent through a CPLD, so that may be why MTD did not work as well.