On Sunday 25 February 2007, Tejun Heo wrote: > [cc'ing Mark, Bart and Sergei. Hi] > > Alan wrote: > >>> This makes unreliable cable detection even more unreliable. Please > >>> consider for -stable. Thanks. > > > > At minimum you also need to stop doing drive side detect for PATA_CBL_80 > > as many controllers don't do both so if you've got host side detect that > > is what you must trust. > > > > Fixed that in my internal tree and it seems happier > > It seems libata is wrong about device side cable detection. Device side > cable detection tries to detect host side capacitor connected to PDIAG-, > depends on the slave device releasing PDIAG- signal. > > According to Annex B of ATA/ATAPI-5, IDENTIFY should be issued to the > slave device first to ensure that it releases PDIAG- and then use the > cable detection result from the master device. As we IDENTIFY master > first right after reset, slave if present is driving PDIAG-, so the > master on IDENTIFY always thinks the capacitor is present and 40c limit > is always applied. > > IDE is better off because it doesn't reset before IDENTIFYing and it's > likely that BIOS has issued some commands to the slave device prior to > passing control to OS thus making it release PDIAG-. > > 1. Device side cable detection can only be used to limit speed because > if motherboard doesn't have capacitor attached to PDIAG-, the test > result always indicates 80c. > > 2. Host side detection involves issuing commands to attached devices > because it depends on the slave device releasing PDIAG-, so most > controllers do cable detection in BIOS and just put the result in PCI > config region or wherever. We dunno how BIOS does it exactly but many > of them probably consider device side detection result as well. > > So, considering #1 and #2, it might be best to just believe what the > controller (BIOS) says and not bother about device side detection. In > fact, we've been effectively ignoring device side detection result > before my "fix" for device side cable detection. > > What do you think? Why can't libata do the right thing and just send IDENTIFY command to the slave device first? Bart - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
