On Thu, Jul 18, 2013 at 14:30 -0700, Peter LaDow wrote: > > We are still stumped on this one, but during a review of the system > setup one thing came up that we aren't sure about is the device tree > and the DMA engine. > > It does seem that for incoming PCI transactions the Freescale DMA > engine is not used. And in our device tree we have the DMA engine > commented out. That is, the "fsl,mpc8349-dma" and "fsl,elo-dma" > compatible items are not present in the FDT. > > I don't suppose this could be a problem?
Can't tell whether it helps or whether I'm telling you what's already known, but here we go: Some Freescale SoC's don't have "_the_ DMA", but instead several of them. Many peripherals have a DMA engine of their own, which you won't notice as a separate entity from the software POV (typically ethernet, USB, PCI, partially video in and out, even coprocessor may have dedicated DMA engines which they might take care of themselves). The thing that you do see (in the device tree, as a software controllable entity) is the "general purpose DMA" with user servicable channels. This one is may be used for serial communication via UART or SPI, or SDHC/MMC, or peripherals attached to the EMB. Sometimes it's called "DMA2" to reflect that there are others as well. So: No, not having to fiddle with DMA stuff when doing PCI need not be a problem, it's actually expected. But since a DMA engine might be involved (that's just not under your command), the accompanying problems may arise. You may need to flush CPU provided data upon write before telling an external entity to access it, and may need to invalidate caches (to have data re-fetched) before the CPU accesses what an external entity did manipulate. And this applies to both payload data as well as management data (descriptors) if the latter apply to the former. HTH virtually yours Gerhard Sittig -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr. 5, D-82194 Groebenzell, Germany Phone: +49-8142-66989-0 Fax: +49-8142-66989-80 Email: off...@denx.de _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
