On Thu, Sep 25, 2008 at 10:31 AM, Jan Stary <[EMAIL PROTECTED]> wrote: > on 4.3 GENERIC.MP (dmesg bellow), this is my disk: > > wd0 at pciide1 channel 0 drive 0: <WDC WD2500YS-01SHB1> > wd0: 16-sector PIO, LBA48, 239371MB, 490232639 sectors > wd0(pciide1:0:0): using PIO mode 4, Ultra-DMA mode 5 > > Now, atactl tells me that the disk can do ATA-7 (aka UDMA6): > > # atactl wd0 identify > [...] > Device supports the following standards: > ATA-1 ATA-2 ATA-3 ATA-4 ATA-5 ATA-6 ATA-7 > [...] > > The flags for the wd device are 0x0 in the kernel, which > (as man wd says) means > > The special setting 0x0000 means ``use whatever the drive > claims to support''. > > Hence my first question: why does wd0 only use Ultra-DMA mode 5 > (as per dmesg) when it is capable of Ulra-DMA mode 6 (as per atactl)? > > Also, if I set the wd flags explicitly to 0x0eac (= 1110 1010 1100), > it still user only Ultra-DMA mode 5 (instead ow 110 = 6 as specified). > Why is that? > > Also, how do people specify Ultra-DMA mode 7? The setting of 0x1111 > has the special meaning of disabling Ultra-DMA altogether (man wd says).
The entirely unhelpful answer is "does it really matter?". I think practical differences for udma stopped somewhere around 3 or 4. It's also possible that your controller is limited by the pciide driver to a certain mode. You can check the source, but it's nobody's favorite driver for a reason.
