linux-kernel - RE: [PATCH -mm 0/2] RapidIO: Changes to handling of RIO switches

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Message-ID: <0CE8B6BE3C4AD74AB97D9D29BD24E55201445906@CORPEXCH1.na.ads.idt.com>
Date:	Fri, 22 Oct 2010 09:47:46 -0700
From:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
To:	"Micha Nelissen" <micha@...i.hopto.org>
Cc:	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<linuxppc-dev@...ts.ozlabs.org>,
	"Matt Porter" <mporter@...nel.crashing.org>,
	"Li Yang" <leoli@...escale.com>,
	"Kumar Gala" <galak@...nel.crashing.org>,
	"Thomas Moll" <thomas.moll@...go.com>
Subject: RE: [PATCH -mm 0/2] RapidIO: Changes to handling of RIO switches

Micha Nelissen <micha@...i.hopto.org> wrote:
> 
> Alexandre Bounine wrote:
> > 1. Using one storage location common for switches and endpoints
eliminates
> > unnecessary device type checks during maintenance access operations.
> > While destination IDs and hop counts have different meaning for
endpoints and
> > switches, this does not prevent us from storing them in the primary
RIO device
> > structure (rio_dev) for both types.
> 
> How can you say this? The two variables have different meanings, this
> logically implies you can't merge them. So how do you say 'this does
not
> prevent us from ...' without providing a reason?

Looks like I formulated it bad - better would be: they have different
interpretation by hardware but logically in RapidIO they have single
role - destid/hopcount are a device coordinates in the RIO network used
to access that device.

> > 2. Convert RIO switch device structures (rio_dev + rio_switch) into
single
> > allocation unit. This change is based on the fact that RIO switches
are using
> > common RIO device objects anyway. Allocating RIO switch objects as
RIO devices
> > with added space for switch information simplifies handling of RIO
switch device
> > objects.
> 
> I still don't think that's a good idea because the rdev->rswitch
pointer
> can be defined to point to the switch that a given rio_dev is
connected
> to. This is useful for quick lookups. How else can to know to which
> switch a given device is connected?

rdev->rswitch is not a pointer to the entire switch device object - it
is a pointer to the switch specific extension associated with given
rio_dev (if applicable). There is no other role for rdev->rswitch.

Why would you keep a pointer to device data extension instead of the
pointer to attached device object itself?

BTW, I have back and forward links added in previous patches and only
one link that may be added later is a forward link from mport to the
attached rio_dev (ptr to rio_switch will not work here because it can be
switchless connection). But this reference has to be added into
rio_mport.
 
Alex.

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