Re: [PATCH] libata: add enclosure management support

[Kristen Carlson Accardi <kristen.c.accardi@intel.com>]

On Thu, 17 Jan 2008 16:50:42 -0600
James Bottomley <James.Bottomley@HansenPartnership.com> wrote:

> On Tue, 2008-01-15 at 16:44 -0800, Kristen Carlson Accardi wrote:
> > Add Enclosure Management support to libata and ahci.
> > 
> > This patch adds support for the LED protocol, as defined in the
> > AHCI spec. It adds a generic em_message and em_type sysfs entry per
> > host.  It also adds a sw_activity field per existing drive.
> > 
> > The em_message field can be used by the driver to take enclosure
> > management commands from userspace.  In the case of the LED
> > protocol, writes and reads from em_message correspond to the LED
> > message format as defined in the AHCI spec.
> > 
> > em_message type is a read only file that displays the current
> > enclosure management protocol that is used by the driver.
> > 
> > sw_activity is used by drivers which support software controlled
> > activity LEDs. It has the following valid values:
> > 
> > 0	OFF - the LED is not activated on activity
> > 1	BLINK_ON - the LED blinks on every 10ms when activity is
> > detected. 2	BLINK_OFF - the LED is on when idle, and blinks
> > off every 10ms when activity is detected.
> > 
> > It's important to note that the user must turn sw_activity OFF it
> > they wish to control the activity LED via the em_message file.
> 
> One of the things we really need to do is to get some type of generic
> enclosure support.  I note that ahci support three standard eclosure
> management protocols (SAF-TE, SES-2, SFF-8485 SGPIO) as well as the
> one proprietary one you've chosen to implement.  Is that because
> no-one in the field has actually connected AHCI up to anything
> supporting one of the standard protocols?
> 
> I'm looking at this from slightly the other way around:  the SAS
> protocol is virtually mandating SFF-8485 as the enclosure protocol to
> the point that it's actually built into the sas management
> protocol ... I was starting to wonder how we should be taking
> advantage of this.
> 
> The implementation probably should be generic (above SCSI or IDE or
> ATA) but it would obviously need to tap into the
> subsytem/transport/device specific pieces, so possibly block looks to
> be the right place to start?
> 
> James
> 
> 

I originally thought to try to make a generic enclosure management
framework that we could hook individual EM protocols into.  Then I
started to wonder why we needed to add knowledge of these protocols
into the kernel.  At least the AHCI hardware which I'm familiar with,
has no need to know anything about the protocol.  It abstracts
everything into just a message.  So, the design that I did in this
patch does the same thing.  You export the type of protocol the driver
is configured to accept, then the message buffer and leave it up to
user space to understand the individual protocol.  This works for all
supported EM protocols.  As far as I can see, most of these management
protocols are better suited to being implemented in user space
anyway. 

As far as block, I'm not sure that makes sense, but maybe I'm
misunderstanding what you want. The em message needs to be associated
with the controller, not with individual devices.  The reason for this
is that the user may wish to locate a drive bay that has no disk in
it, so they need to be able to send enclosure messages regardless of
whether there's a block device associated with it. 

Kristen