Re: [PATCH 1/4] sas: add flag for locally attached PHYs

Luben Tuikov
2005-10-20T16:08:29Z

On 10/20/05 11:49, Christoph Hellwig wrote:
> <lots of useless rants snipped>

Hi Christoph,

For some reason I thought that I was quoting specs
and showing constructive ideas (i.e. things you can sit down
and start coding).

I'm sorry that you feel that it is "useless rants".

On a topic note: It appears that the "sas transport attributes" are
nothing more than SDI/CSMI.

> Yes, we have two cases, local phy and phy on an expander. The proper
> way to support remote phys is via smp passthru as we hopefully agree.
> Right now the sas transport class doesn't do smp passthru (although
> I'm working on it) so we only implement local link stats.

You are so much better off implementing SDI/CSMI as per the spec.

Normally, at companies, projects have a "specificaion" and "required
functionality". What is the "specificaion" and "required functionality"
at hand?

Note that there are LSI/HP customers who are completely _happy_
to use CSMI as provided by LSI and they are not interested in
what-have-you-not.

The easiest way to make those customers happy and keep them happy is
to provide general SDI/CSMI facitliy and _you have a spec on that_.

> Once we have
> smp passthru we can support link stats, in one of two ways:
>
> - do it in userland as in your example program. in that case we don't
> need to do anything in kernel land and need the local_attached flag
> to disable this functionality for expander phys.
> - do it in kernel, in which case the transport class must call the smp
> passthru entry point of the driver to query link stats, so it needs
> the local_attached flag aswell for that.
>
> What's your problem with the flag now?

It is ugly, it is a (brown) paper bag solution, it is a work around.

Take a look at the phy attributes as per the SAS spec. Then take
a look at struct sas_phy in include/scsi/sas/sas_class.h. Do you
see such a flag in either reference?

Luben
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