Messages in this thread | | | Date | Fri, 19 Mar 2004 19:14:53 -0500 | From | Jeff Garzik <> | Subject | Re: [PATCH] barrier patch set |
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Bartlomiej Zolnierkiewicz wrote: > The fact that spec says "supported" not "enabled" in description of word86 > makes me wonder - can they be disabled? (FLUSH CACHE is mandatory for General > feature set and FLUSH CACHE EXT is mandatory if 48-bit LBA is supported)
Yes, that's why there are separate 'supported' and 'enabled' bits for each feature.
Words 82-84 are 'supported' bits. Words 85-87 are 'enabled' bits. These bits mirror each other, i.e. Word 83 and Word 86 have basically the same bits, except that Word 86 definitions change _slightly_ since the only bits that are relevant are the ones for features that can be disabled/enabled.
You use set-features command to enable and disable these features, and then the result shows up in subsequent identify-device command output.
If the driver is testing for a capability but does not enable it, then always use the 'enabled' set of bits, not the 'supported' set of bits.
> Jeff, please note that these bits were introduced by ATA-6 spec > and take a look at ATA-5 spec: > > ... > FLUSH CACHE > General feature set > - Mandatory for all devices > ... > > and ATA-4 spec: > > ... > FLUSH CACHE > General feature set > - Optional for all devices > ... > > IMO to test if FLUSH CACHE works we should just issue it during disk setup > and check result. This way we can use FLUSH CACHE also on < ATA-6 devices > (there is a lot of them).
I disagree. "just issue it" is how those LG cdrom drives got cooked.
LG cdrom drives indicated in their identify-packet-device page that flush-cache was not supported... and then re-used the flush-cache ATA opcode for their vendor-specific download-firmware command. Combine that with a Linux patch that didn't properly check for flush-cache support. Result: brick.
All drives that support flush-cache list the relevant bits in identify-device, even on pre-ATA-6 devices. Whether the feature was optional or mandantory, we can check the feature bits.
Jeff
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