On Mon, 14 Dec 2009 09:57:55 -0500 Valdis.Kletnieks@xxxxxx wrote: > On Mon, 14 Dec 2009 07:58:01 GMT, tip-bot for FUJITA Tomonori said: > > Commit-ID: 06f8bda8324fa8bf39eed81d8b3df08063a37696 > > > x86: Remove usedac in feature-removal-schedule.txt > > > The usedac option enables us to stop via_no_dac() setting > > forbid_dac to 1. That is, someone who uses VIA bridges can use > > DAC with this option even if some of VIA bridges seem to be > > broken about DAC. > > Does there exist real hardware where this makes sense? If the chipset > detects as "broken-DAC", is it in fact safe to use? Not safe. Probably, you would see data corruption. arch/x86/kernel/pci-dma.c says: /* Many VIA bridges seem to corrupt data for DAC. Disable it here */ Seems that some of VIA bridges were fine. So this option made sense with some hardware. I'm not sure if there are still users of this option now. > Or is it similar to > the 'force-enable HPET' code for some older boxes, where the HPET was in > fact there but simply not advertised, so going ahead and using it was > in fact perfectly safe? Allowing the use of "working but not advertised" > is probably a good thing, allowing the use of known-broken probably isn't. > > If it's just unadvertised, I wonder if if there's a way to write a quirk > for VIA systems that will detect the situation and enable the support? I guess that we could however it doesn't worth adding tricks for old hardware. -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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