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> On Sat, 15 Feb 2003, Roger Luethi wrote: > > > > Thanks for raising that issue. It is my understanding that PIO ops are > > synchronous (on IA-32). If that is correct, problems should only occur if > > the driver is built with MMIO support, no? > > No, even PIO ops are asynchronous. They are _more_ synchronous than the > MMIO ones (I think the CPU waits until they hit the bus, and most bridges Hmmm... A recent thread on PCI write posting seemed to confirm my view [1]. What am I missing here? ------------------------------ cut here ----------------------------------- From: Alan Cox <alan@lxorguk.ukuu.org.uk> Subject: Re: Linux 2.4.21-pre3-ac4 Date: 12 Jan 2003 20:40:54 +0000 On Sun, 2003-01-12 at 19:51, Benjamin Herrenschmidt wrote: > What about PCI write posting ? How can we enforce the 400ns delay here ? For i/o space it is ok as in*/out* are synchronous. For mmio right now I don't know. I need to talk to Andre about that for SATA. I guess for the PPC its going to be fun [...] ------------------------------ cut here ----------------------------------- > don't need a IO read to force it out. But considering the wide variety of > PCI bridges out there I bet there are some that will post even PIO writes > and might hold on to them for some time, especially if other activity like > DMA keeps the bus busy. There was some talking about hwif->IOSYNC() (for IDE). That might be interesting for other devices, too. It could resolve to a nop for synchronous operations, and say a read* for MMIO. IMHO it shouldn't be up to a driver maintainer to figure out what sync op some arch the driver may run on needs. What a maintainer typically _can_ provide is type of operation (MMIO/PIO) and a register that is considered safe for a sync read. Roger [1] http://marc.theaimsgroup.com/?l=linux-kernel&m=104240180906935&w=4 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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