Re: [Xen-devel] AHCI question

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Nov 22, 2010 at 12:07:58PM -0500, Kamala Narasimhan wrote:
> It is a bare minimal driver in Xen (under development) which is
> invoked upon a system crash to persist crash dump data to disk by
> issuing commands through the pre-programmed HBA registers.  Unlike a
> full fledged AHCI driver, we do not initialize the very many memory
> regions used to communicate between the device and the system software
> as in our case the dom0 would have already done all that.  We simply
> map those memory regions that dom0 has already setup and issue
> commands to copy data to disk.  And that issuing of command part is
> not succeeding as I would expect.

I think you are better of asking on the ahci-devel, and as well folks
on the kdump mailing list as they had to wrestle with these kinds of
issues already.

Thought .. why not use the kdump kernel?
> 
> Kamala
> 
> On Mon, Nov 22, 2010 at 11:42 AM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:
> > On Mon, Nov 22, 2010 at 09:51:26AM -0500, Kamala Narasimhan wrote:
> >> I am writing a polled mode Xen AHCI driver to collect some minimal
> >
> > What is a 'Xen AHCI' driver?
> >
> >> information after a system crash.  As dom0 would have initialized and
> >> used the HBA before we enter the crashing code path, I am not doing
> >> any kind of device initialization within the Xen AHCI driver.  I am
> >> also not setting up interrupts etc. as the driver is used in polled
> >> mode.  I simply map the abar and other memory regions associated with
> >> the device that dom0 has already setup and write to it/read from it as
> >> needed.
> >>
> >> After a crash, within the Xen AHCI driver I am able to get to the pci
> >> space for the device, get valid HBA registers, mapping etc. works but
> >> the HBA does not respond back after I issue a command for execution.
> >> In specific, after I set the port x command issue register (pxci) for
> >> the free slot, that slot is not getting cleared as it should after a
> >> command execution.
> >>
> >> As an experiment to see if anything at all works with respect to
> >> setting/resetting port registers, I simply decided to stop/start the
> >> HBA command engine by setting the ST bit in the command register
> >> (PxCMD) to 0 and then checking if CR, FR bit etc. in PxCMD are reset
> >> by HBA after a ST reset but they remain set.
> >>
> >> I am hoping someone with AHCI experience might be able to shed some
> >> light as to why the HBA is not responding as it should.  Thanks.
> >>
> >> Kamala
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-devel
> >
> 
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