[PATCH 2/2] ARM: dts: imx28: Adjust i2c interrupt bindings

Marek Vasut marex at denx.de
Fri May 24 09:57:23 EDT 2013

Dear Lucas Stach,

> Am Donnerstag, den 23.05.2013, 19:51 +0200 schrieb Alexandre Belloni:
> > Hi,
> [...]
> > > So while we _might_ be able to get the PIO mode to work on the i.MX23
> > > there is nothing in the doc stating that it's even meant to work. Even
> > > while PIO and DMA mode use the same internal mechanisms, there's still
> > > plenty of opportunities of fail in there. After all PIO mode relies on
> > > reading a debug register in the course of normal operation.
> > > 
> > > Only more extensive experimentation could show if we are in fact able
> > > to make it work, a first shot of using PIO mode on MX23 failed, so it
> > > might as well be that Juergens quick fix is correct and we have to
> > > disable PIO mode on MX23 altogether. That said please stop slapping
> > > the word "hack" over this patch until proven otherwise.
> > 
> > Still, Fabio and I have been experiencing the one second delay on
> > i.mx28. From my experience, it appeared between 3.7 and 3.9, see:
> > http://www.spinics.net/lists/linux-i2c/msg11985.html. I still didn't
> > take the time to investigate more yet but it confirms that PIO mode is
> > working on i.mx28 though with an annoying delay.
> Just for the record: I know that PIO mode is functional on i.MX28
> because I have it working on one of our customer boards. I am rather
> much surprised it's still not working well for you, but haven't had a
> chance to investigate yet. The i.MX28 RM explicitly describes how to
> work with the PIO mode, so if it's not working this is bug somewhere.

I won't be surprised if there was more than one. The RM describes something , 
but has many flaws. I'm sure you noticed that yourself.

> This thread/patch is about a whole different problem, namely PIO mode
> being non-functional on i.MX23. As the i.MX23 RM doesn't describe the
> PIO mode, there is no indication that it's even meant to work on this
> chip.

I'm not against the patch per-se, but can we not get the best of this and 
instead try some more to fix the PIO on MX23 so the MX23 users won't suffer 
performance degradation on already weak CPU?

Best regards,
Marek Vasut

More information about the linux-arm-kernel mailing list