Re: [PATCH 0/9] misc AHCI cleanups

[Niklas Cassel <Niklas.Cassel@wdc.com>]

On Wed, May 17, 2023 at 01:06:06PM -0400, John Snow wrote:
> On Fri, Apr 28, 2023 at 9:22 AM Niklas Cassel <nks@flawful.org> wrote:
> >
> > From: Niklas Cassel <niklas.cassel@wdc.com>
> >
> > Hello John,
> >
> 
> Hi Niklas!
> 
> I haven't been actively involved with AHCI for a while, so I am not
> sure I can find the time to give this a deep scrub. I'm going to
> assume based on '@wdc.com` that you probably know a thing or two more
> about AHCI than I do, though. Can you tell me what testing you've
> performed on this? As long as it doesn't cause any obvious
> regressions, we might be able to push it through, but it might not be
> up to me anymore. I can give it a review on technical merit, but with
> regards to "correctness" I have to admit I am flying blind.

Hello John,

The testing is mostly using linux and injecting NCQ errors using some
additional QEMU patches that are not part of this series.

> 
> (I haven't looked at the patches yet, but if in your commit messages
> you can point to the relevant sections of the relevant specifications,
> that'd help immensely.)
> 
> > Here comes some misc AHCI cleanups.
> >
> > Most are related to error handling.
> 
> I've always found this the most difficult part to verify. In a real
> system, the registers between AHCI and the actual hard disk are
> *physically separate*, and they update at specific times based on the
> transmission of the FIS packets. The model in QEMU doesn't bother with
> a perfect reproduction of that, and so it's been a little tough to
> verify correctness. I tried to improve it a bit back in the day, but
> my understanding has always been a bit limited :)
> 
> Are there any vendor tools you're aware of that have test suites we
> could use to verify behavior?

Unfortunately, I don't know of any good test suite.

> A question for you: is it worth solidifying which ATA specification we
> conform to? I don't believe we adhere to any one specific model,
> because a lot of the code is shared between PATA and SATA, and we "in
> theory" support IDE hard drives for fairly old guest operating systems
> that may or may not predate the DMA extensions. As a result, the
> actual device emulation is kind of a mish-mash of different ATA
> specifications, generally whichever version provided the
> least-abstracted detail and was easy to implement.
> 
> If you're adding the logging features, that seems to push us towards
> the newer end of the spectrum, but I'm not sure if this causes any
> problems for guest operating systems doing probing to guess what kind
> of device they're talking to.
> 
> Any input?

I agree.

In my next series, after we have General Purpose Logging support,
I intend to bump the major version to indicate ACS-5 support.
I will need to verify that we are not missing any other major
feature from ACS-5 first though (other than GPL).


Kind regards,
Niklas