linux-kernel - RE: [PATCH 2/7] RapidIO: Add switch locking during discovery

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Date:	Thu, 25 Feb 2010 06:53:04 -0800
From:	"Bounine, Alexandre" <Alexandre.Bounine@....com>
To:	"Micha Nelissen" <micha@...i.hopto.org>
Cc:	<mporter@...nel.crashing.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<linux-kernel@...r.kernel.org>, <thomas.moll@...go.com>,
	<thomas.moll.ext@....com>, "Alexandre Bounine" <alexb@...dra.com>
Subject: RE: [PATCH 2/7] RapidIO: Add switch locking during discovery

Micha Nelissen wrote:
> 
> Alexandre Bounine wrote:
> > +				/* Attempt to acquire device lock */
> > +				rio_mport_write_config_32(port, destid,
> > +							  hopcount,
> > +
RIO_HOST_DID_LOCK_CSR,
> > +
port->host_deviceid);
> > +				rio_mport_read_config_32(port, destid,
hopcount,
> > +					RIO_HOST_DID_LOCK_CSR, &result);
> > +				while (result != port->host_deviceid) {
> 
> It's better to abstract the locking of a device into a new function,
> rio_lock_device / rio_unlock_device.
> 
> Then you can use those in rio_get_route_entry and rio_add_route_entry.

Agree. Plus, adding a "lock" parameter to
rio_get_route_entry/rio_add_route_entry to avoid excessive locking
requests when scanning entire table. I will do it in next version or as
additional patch: I have to address locking anyway for future changes.
    
> 
> > @@ -1027,6 +1090,13 @@ int __devinit rio_disc_mport(struct rio_
> > +
> > +		/* Read DestID assigned by enumerator */
> > +		rio_local_read_config_32(mport, RIO_DID_CSR,
> > +					 &mport->host_deviceid);
> > +		mport->host_deviceid = RIO_GET_DID(mport->sys_size,
> > +
mport->host_deviceid);
> > +
> 
> This fixes something else, should be a separate patch.

This sets an ID used for locking during discovery. On a startup only
enumerator's ID is set to the specified value. All discovering agents
have this ID set to -1. After enumeration is completed it is safe to
initialize host_deviceid for agents as well.

Alex.

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