Messages in this thread | | | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: [PATCH] barrier patch set | Date | Sat, 20 Mar 2004 01:40:59 +0100 |
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On Saturday 20 of March 2004 01:14, Jeff Garzik wrote: > 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.
This is quite obvious but I am talking about confusing wording in description of word86 - for some features 'enabled' is used and for others 'supported'
> > 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.
I'm aware of LG fun. Jens already stated that current barrier implementation is disk-only and I'm talking about disks only.
If anybody reused CACHE FLUSH opcode for disk drive he/she deserves to loose. 8)
> 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.
Hm. so this is undocumented in the spec?
Bartlomiej
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