Re: [RFC] i.MX25/35/SDHCI: switch off DMA usage

From: Juergen Borleis
Date: Tue Apr 14 2015 - 05:39:53 EST


On Friday 27 March 2015 12:44:03 Dong Aisheng wrote:
> On Fri, Mar 27, 2015 at 11:52:04AM +0100, Juergen Borleis wrote:
> > DMA and the required overhead on very small data blocks seems an
> > expensive operation. Due to erratum ENGCM07207 for i.MX25 and i.MX35 SoCs
> > the support for multiblock transfers is disabled which results into a
> > huge amount of single 512 byte sector transfers and interrupts. This
> > slows down the transmission speed to below 500 kiB/s (even at 50 MHz SD
> > card clock). Using PIO instead of DMA to avoid ENGCM07207 happens and
> > re-enabling multiblock transfers again improve the transmission
> > capability up to about 2.5 MiB/s.
> >
> > I'm still not sure if ENGCM07207 is related to DMA only and can not
> > happen when PIO is used instead. Someone out there with experience
> > regarding this topic?
> The errata does not state it's related to DMA only.
> I could double check with our IC guys to confirm it.

Gentle ping.


Pengutronix e.K.                              | Juergen Borleis             |
Industrial Linux Solutions      | |
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