Understanding SAS

Understanding SAS

[Madhukar G]

Hi All,

I'm new to SAS architecture. I have sas1r10.pdf with me for
understanding the protocol. I'm looking at the sources available at
scsi/libsas.

I was looking at task management function sequence and non-data
command sequence for SSP frames in the specification. But i could not
map the same in source code. Can some help me understand in which
functions these sequences of SSP frames are handled.

Any help is much appreciated.

Thank You.

Regards,
Madhukar

Re: Understanding SAS

[Madhukar G]

Thanks for the info. Where can i download the mvsas patch. Currently
i'm using 2.6.28 kernel.

Regards,
Madhukar

2009/3/26 Ying Chu <jasonchu@marvell.com>:
> You can consult the new mvsas patch set pending to kernel.
>
>
> -----Original Message-----
> From: linux-scsi-owner@vger.kernel.org [mailto:linux-scsi-owner@vger.kernel.org] On Behalf Of Madhukar G
> Sent: 2009年3月24日 20:35
> To: linux-scsi@vger.kernel.org
> Subject: Understanding SAS
>
> Hi All,
>
> I'm new to SAS architecture. I have sas1r10.pdf with me for understanding the protocol. I'm looking at the sources available at scsi/libsas.
>
> I was looking at task management function sequence and non-data command sequence for SSP frames in the specification. But i could not map the same in source code. Can some help me understand in which functions these sequences of SSP frames are handled.
>
> Any help is much appreciated.
>
> Thank You.
>
> Regards,
> Madhukar
> --
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Understanding SAS

[Madhukar G]

Hi All,

I'm understanding SAS architecture for adaptec controller. I'm using
the source adp94xx for the same. I was able to understand all the
infomation unit flow but i'm stuck with one problem. I was not able to
trace when task management IU shall be invoked.
Do i need any special app to test task management IU?
Is SCSI layer responsible for invoking task management IU?

Thanks.
madhukar

Re: Understanding SAS

[James Bottomley]

On Fri, 2009-07-31 at 17:26 +0530, Madhukar G wrote:
> I'm understanding SAS architecture for adaptec controller. I'm using
> the source adp94xx for the same. I was able to understand all the
> infomation unit flow but i'm stuck with one problem. I was not able to
> trace when task management IU shall be invoked.
> Do i need any special app to test task management IU?
> Is SCSI layer responsible for invoking task management IU?

I don't understand what you mean by IU:  SAS tends to think in terms of
frames (at the transport layer).  Information Units as used by the SAS
protocol means specific SSP frames.  Task Management in SAS has to
include SMP, STP and SATA as well.

However, SAM task management functions all map to the callbacks in
struct sas_domain_function_template which are called by libsas.  These
callbacks are also used for all other frame error handling.

James

Re: Understanding SAS

[Madhukar G]

> However, SAM task management functions all map to the callbacks in
> struct sas_domain_function_template which are called by libsas.  These
> callbacks are also used for all other frame error handling.
>

I understand the callbacks used for error handling. For which types of
errors these callbacks invoked? When do these error occur? Which layer
is responsible for invoking these callback.. Is it SCSI layer/ File
System or Application Client?

Pardon me if these questions sounds silly. but i'm in process of
understading the sequence.

I tried copying data to and from SAS controller and aborted in
between. But i donot see any error handlers being invoked.

Thanks and Regards,
madhukar
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Re: Re: Understanding SAS

[Madhukar G]

> If you look into the libsas source you will find that lldd_abort_task will
> be
> called when task flag is set to SAS_TASK_STATE_ABORTED ,that means the
> task is timeout by sas layer, then sas layer will abort it. other other case
> are
> during error recovery, when scsi ml scsi_error_handler is scheduled to run.
>

Thank you for the reply. Is there any way i can test this sequence. I
would like to explicitly set SAS_TASK_STATE_ABORTED and further
invoking error handlers.

Thanks and Regards,
madhukar

Re: Re: Understanding SAS

[Madhukar G]

> Thank you for the reply. Is there any way i can test this sequence. I
> would like to explicitly set SAS_TASK_STATE_ABORTED and further
> invoking error handlers.
>

Does this mean that i do not require any application to invoke error
handlers (task frames / task IU).

Thanks.
madhukar