Re: [Xen-devel] AHCI question

[Kamala Narasimhan <kamala.narasimhan@xxxxxxxxx>]

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.

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
>>
>> _______________________________________________
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>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>

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