On Mon, Jun 14, 2004, David Brownell <[EMAIL PROTECTED]> wrote: > Alan Cox wrote: > >On Llu, 2004-06-14 at 17:11, Alan Stern wrote: > > > >>The computers you mentioned use PPC processors. Do you know if these > >>cache-line effects are equally important for Intel x86 machines? > > > > > >x86 systems are supposed to be cache coherent in this situation. The > >bridge will untangle the mess as neccessary. The PC is the unusual one > >here - most other platforms (eg mips) behave like the PPC > > Seems like the dma_alloc_coherent() API spec can't be > implemented on such machines then, since it's defined > to return memory(*) such that: > > ... a write by either the device or the processor > can immediately be read by the processor or device > without having to worry about caching effects. > > Seems like the documentation should change to explain > under what circumstances "coherent" memory will exhibit > cache-incoherent behavior, and how to cope with that. > (Then lots of drivers would need to change.) > > OR ... maybe the bug is just that those PPC processors > can't/shouldn't claim to implement that API. At which > point all drivers relying on that API (including all > the USB HCDs and many of the USB drivers) stop working. > > (*) DMA-API.txt uses two terms for this: "coherent" and "consistent". > DMA-mapping.txt only uses "consistent".
I'm having trouble understanding exactly what the problem is. Is the problem that the device (or maybe PCI bridge) is caching data and then overwriting stale data to the software portion of the QH descriptor? JE ------------------------------------------------------- This SF.Net email is sponsored by The 2004 JavaOne(SM) Conference Learn from the experts at JavaOne(SM), Sun's Worldwide Java Developer Conference, June 28 - July 1 at the Moscone Center in San Francisco, CA REGISTER AND SAVE! http://java.sun.com/javaone/sf Priority Code NWMGYKND _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
