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 07:31:22 -0700
From:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	<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>,
	"Micha Nelissen" <micha@...i.hopto.org>
Subject: RE: [PATCH v2 03/10] RapidIO: Use stored ingress port number instead of register read

Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > @@ -219,6 +219,7 @@ struct rio_net {
> >  /**
> >   * struct rio_switch - RIO switch info
> >   * @node: Node in global list of switches
> > + * @rdev: Associated RIO device structure
> >   * @switchid: Switch ID that is unique across a network
> >   * @hopcount: Hopcount to this switch
> >   * @destid: Associated destid in the path
> > @@ -234,6 +235,7 @@ struct rio_net {
> >   */
> >  struct rio_switch {
> >  	struct list_head node;
> > +	struct rio_dev *rdev;
> >  	u16 switchid;
> >  	u16 hopcount;
> >  	u16 destid;
> 
> What is the locking for rdev?

This question prompted me consider the following change:

Because the rio_switch structure (in current implementation) is a
dynamically allocated part of rio_dev, I think it may be simpler to
combine them into single allocation by using zero length array
declaration:

struct rio_dev {
    struct list_head global_list;
    struct list_head net_list;
    .....
    ..... rest of rio_dev
    .....
    struct rio_switch switch[0];
}

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;
	}    

And this looks better aligned with RapidIO definitions - both: endpoints
and switches are RIO devices. The current implementation of rio_dev
somewhat separates rio_switch from its common part (this is why I have
added that link into rio_switch). We may keep using the pointer to
associated rio_dev, but reworking the rio_dev structure seems better way
to me.

Please, let me know what do you think about this conversion. And if
there are no objections I will make a patch.

Alex.
     
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