linux-kernel - Re: [PATCH v2 03/10] RapidIO: Use stored ingress port number instead of register read

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Date:	Mon, 20 Sep 2010 22:40:56 +0200
From:	Micha Nelissen <micha@...i.hopto.org>
To:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Thomas Moll <thomas.moll@...go.com>,
	Matt Porter <mporter@...nel.crashing.org>,
	Li Yang <leoli@...escale.com>,
	Kumar Gala <galak@...nel.crashing.org>
Subject: Re: [PATCH v2 03/10] RapidIO: Use stored ingress port number instead
 of register read

Hi Alex,

Bounine, Alexandre wrote:
> struct rio_dev {
>     struct list_head global_list;
>     struct list_head net_list;
>     .....
>     ..... rest of rio_dev
>     .....
>     struct rio_switch switch[0];
> }

It makes sense to let rio_dev structures point to the switch they are 
attached to. That can be useful in various situations, but is not 
possible with this setup.

If a rio_dev is a switch then rdev->rswitch->rdev == rdev holds.

> This will remove extra memory allocation, remove overlapping structure
> members and clean code sections like one shown below:
> 
> 	u8 hopcount = 0xff;
> 	u16 destid = rdev->destid;
> 
> 	if (rdev->rswitch) {
> 		destid = rdev->rswitch->destid;
> 		hopcount = rdev->rswitch->hopcount;
> 	}    

Note that it is possible for rdev->destid to differ from 
rdev->rswitch->destid even if rswitch->rdev == rdev (for non-hosts i.e. 
agents). rswitch->destid is the destid by which we discovered the switch 
(and can reach it) but rdev->destid is the actual id given to the switch.

Micha
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