From mboxrd@z Thu Jan  1 00:00:00 1970
From: arnd@arndb.de (Arnd Bergmann)
Date: Mon, 16 Jun 2014 18:42:10 +0200
Subject: [PATCH RFC v1 1/2] documentation/iommu: Add description of
 Hisilicon System MMU binding
In-Reply-To: <20140616162653.GV16758@arm.com>
References: <1401975430-2648-1-git-send-email-thunder.leizhen@huawei.com>
 <20140606110652.GB4116@e103592.cambridge.arm.com>
 <20140616162653.GV16758@arm.com>
Message-ID: <5537408.I9tiuCA96J@wuerfel>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Monday 16 June 2014 17:26:53 Will Deacon wrote:
> On Fri, Jun 06, 2014 at 12:07:11PM +0100, Dave Martin wrote:
> > On Fri, Jun 06, 2014 at 08:48:26AM +0200, Arnd Bergmann wrote:
> > > On Thursday 05 June 2014 21:37:09 Zhen Lei wrote:
> > > 
> > > > +- smmu-masters  : A list of phandles to device nodes representing bus
> > > > +                  masters for which the SMMU can provide a translation
> > > > +                  and their corresponding StreamIDs (see example below).
> > > > 
> > > 
> > > We're currently in the process of defining a generic binding for IOMMUs.
> > > 
> > > While the smmu-masters property was copied from an existing binding,
> > > I think we will end up migrating away from that towards a common way
> > > to express those things, and we shouldn't add another one doing this
> > > in a nonstandard way. Please have a look at the latest discussion
> > > about the iommu binding using #iommu-cells and a reference from the
> > > master to the iommu and see if you can migrate your code to use that.
> > 
> > Thanks for making this point -- I was going to do so yesterday but then
> > hesitated due to uncertainty about whether this should really be a new
> > driver.
> > 
> > Either way, it would be very valuable at least to attempt to describe
> > the Hisilicon SMMU implemenation using the new proposals, since that is
> > a good test of how reusable the proposed generic binding actually is.
> 
> If this ends up being an addition to the existing ARM SMMU driver, I'm
> really not keen on using the new DT bindings. We're already stuck with
> the old bindings for that driver -- supporting both old and new in the
> same code only buys us maintenance headaches and pointless divergence
> within the driver.

We have to migrate the driver to the new binding anyway, it may be
a bit painful, but there are not really any users yet so there
is a chance we can remove the nonstandard code at some point,
perhaps in a few years.

	Arnd