[PATCH] i2c: mxs: remove broken PIOQUEUE support

Wolfram Sang w.sang at pengutronix.de
Thu Nov 1 12:08:28 EDT 2012

On Thu, Nov 01, 2012 at 03:28:17PM +0100, Marek Vasut wrote:
> Dear Wolfram Sang,
> > This I2C master can do DMA and PIOQUEUE (PIO with FIFO). Originally,
> > only PIOQEUE

Yup, right!

> > was supported, then DMA support was added. The original
> > intention was to keep PIOQUEUE since it has less overhead what is nice
> > for small transfers. However, runtime switching between PIOQEUE and DMA
> > depending on the transfer size never worked despite a lot of trying.
> > Since PIOQUEUE mode itself was flaky (polling at places where interrupts
> > failed to work) and the implementation also imposed a size limit for
> > transfers, it is best to remove the support altogether which makes the
> > driver a lot cleaner and more robust. If somebody really wants less
> > overhead, plain PIO mode could still be implemented with the addidtional
> > advantage that this mode is also available on MX23, too.
> Yes, looks to be the way to go.
> Reviewed-by: Marek Vasut <marex at denx.de>


BTW have you tried combining all i2c-messages (msgs[]) of the transfer
into one DMA chain? That would reduce overhead, too, no?



Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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