Messages in this thread | | | Date | Mon, 20 Jan 2003 14:00:55 -0500 | From | Jeff Garzik <> | Subject | Re: pci_set_mwi() ... why isn't it used more? |
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On Mon, Jan 20, 2003 at 10:41:35AM -0800, David Brownell wrote: > I was looking at some new hardware and noticed that it's > got explicit support for the PCI Memory Write and Invalidate > command ... enabled (in part) under Linux by pci_set_mwi(). > > However, very few Linux drivers use that routine. Given > that it can lead to improved performance, and that devices > don't have to implement that enable bit, I'm curious what > the story is... > > - Just laziness or lack-of-education on the part of > driver writers? > > - Iffy upport in motherboard chipsets or CPUs? If so, > which ones? > > - Flakey support in PCI devices, so that enabling it > leads to trouble? > > - Something else? > > - Combination of all the above?
You missed the reason entirely ;-)
pci_set_mwi() is brand new, I just added it. Hasn't filtered down to drivers yet. The few drivers that cared prior to its addition, like drivers/net/acenic.c, just hand-coded the workarounds needed for proper MWI support on all chipsets.
pci_set_mwi() would not exist at all, were it not for the existing hardware quirks. (if hardware were sane, drivers would just individually twiddle the _INVALIDATE bit in PCI_COMMAND, and never call functions other than pci_{read,write}_config_word.
Jeff
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