linux-kernel - RE: [PATCH 3/3] omap: add hwspinlock device

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Date:	Thu, 21 Oct 2010 07:26:25 -0500
From:	"Kanigeri, Hari" <h-kanigeri2@...com>
To:	"Kamoolkar, Mugdha" <mugdha@...com>,
	"'Ohad Ben-Cohen'" <ohad@...ery.com>,
	Kevin Hilman <khilman@...prootsystems.com>,
	"Krishnamoorthy, Balaji T" <balajitk@...com>,
	"Kamat, Nishant" <nskamat@...com>
CC:	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>, Tony Lindgren <tony@...mide.com>,
	"Cousson, Benoit" <b-cousson@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	"Anna, Suman" <s-anna@...com>, Simon Que <sque@...com>
Subject: RE: [PATCH 3/3] omap: add hwspinlock device

Mugdha,

> > >>
> > >> This does not require any smart IPC and it will allow us to get
> > rid of
> > >> the omap_hwspinlock_request_specific() API and its early-callers
> > >> requirement.
> > >
> > > Yes, that would indeed simplify things.
> >
> > Balaji, Nishant, are you OK with this ?
> >
> The problem with this approach is that the i2c driver would have to
> sync up on the shared memory location that it uses to share the
> information of the spinlock ID. What location would this be? How would
> the i2c driver on the m3 know about this location? Does this mean
> hard-coding of the shared memory address? If yes, then there would be
> an impact to users if they wanted to change their memory map. Any kind
> of hard-coding of this sort can be painful in such cases, especially
> if it happens in multiple drivers. On the other hand, hard-coding
> (reserving) spinlock IDs is a much safer option and does not impact
> anything else.
> 

We can avoid the hard-coding of shared memory location if I2C Driver maps using iommu some dynamic memory for shared memory location to M3 virtual address and shares this information to I2c driver counter-part on M3 using the IPC call. But this might not be trivial and this would be against what Ohad mentioned about not requiring any smart IPC :).
I prefer hard-coding of spinlock id to keep things simple.

Thank you,
Best regards,
Hari
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