ATA ACPI needs "Mr interpreter, would you please shut up?" flag

Hello, all.

During 2.6.24-rc1, libata enabled ATA-ACPI support by default and there have been a lot of regression reports stemming from it. I have patchset ready to fix most of the problems. With these patches applied, libata should be able to cope with most failures pretty well. There is one remaining issue tho.

libata caches the result of _GTM during controller for later use. The primary use is to peek at how BIOS configured the controller. Some controllers (pata_via and pata_amd) lack proper cable detection and BIOS configured values are used as reference. This caching is done before any other operation is performed on the port to avoid caching corrupted data.

Problem is that _GTM implementation on certain BIOSen crap themselves if invoked on empty channels. However, as written above, because initial _GTM caching is done before any actual operation is performed on the port, libata can't determine whether the port is occupied or not when trying to cache _GTM result. Unfortunately, VIA PATA is on both categories - it needs _GTM caching but can't cope with _GTM invocation on empty ports. Yay!

libata doesn't need _GTM to succeed. If the information can be acquired, it will use it. If not, it will do just fine without it and for pata_via, this works perfectly well because the information is available when actually needed (device present). The only problem is that _GTM evaluation failure will print ugly messages during boot.

We can twist ATA probing such that _GTM caching is done between device detection but before mode is reset to PIO0 but I don't think that's a good idea for two reasons. 1. That would require pushing PIO0 enforcement after reset. IMHO, it's wiser to put controller into PIO0 before initiating reset. 2. Presence detection sometimes requires actually issuing IDENTIFY DEVICE command which in turn needs PIO0 configuration.

So, I think the logical solution here is to tell ACPI interpreter that the _GTM evaluation may fail and there's no need to alert the user about that. Maybe printing with KERN_DEBUG is good enough. libata can print additional message after failure (again w/ KERN_DEBUG) telling the user that there's nothing to worry about.

Thanks.

tejun

I seem to have lost the thread/bug report where we decided that one board always choked on an empty channel. Maybe it's not that and it's just another case of the same issue where our resetting default timing values on the controller before calling _GTM would choke the _GTM method?

Robert Hancock      Saskatoon, SK, Canada
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Home Page: http://www.roberthancock.com/

Could be. Hans' machine on bug 9320 is the affected one (PATA on via CN700). I asked him to test the final version. If it indeed is caused by the same problem, there won't be evaluation failures.

Anyways, table-based implementations like the NVidia and VIA ones are bound to fail on certain conditions. libata reconfigures transfer mode aggressively under certain failure conditions and _GTM invocation will fail if the port is in a mode which is not on ACPI's mode table (which doesn't seem to be too comprehensive anyway). So, there's always possibility of _GTM failure for those boards, which in turn can fail _GTF evaluation.

As _GTM, _STM and _GTF aren't strictly necessary for operation anyway, I think it's better to print ATA ACPI evaluation failure messages using KERN_DEBUG.

Thanks.

tejun

I take it back. I found how to satisfy neurotic BIOSen.

Thanks.

tejun

..

Aaaa.. excellent!