linux-kernel - Re: [PATCH 0/2] crypto: add new driver for Marvell CESA

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Date:	Fri, 17 Apr 2015 17:49:10 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Arnaud Ebalard <arno@...isbad.org>,
	Mark Rutland <mark.rutland@....com>,
	Thomas Petazzoni <info@...e-electrons.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Eran Ben-Avi <benavi@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>, devicetree@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>, Andrew Lunn <andrew@...n.ch>,
	linux-crypto@...r.kernel.org, Kumar Gala <galak@...eaurora.org>,
	Tawfik Bayouk <tawfik@...vell.com>,
	"David S. Miller" <davem@...emloft.net>,
	Lior Amsalem <alior@...vell.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 0/2] crypto: add new driver for Marvell CESA

On Fri, Apr 17, 2015 at 05:01:55PM +0200, Gregory CLEMENT wrote:
> On 17/04/2015 16:50, Maxime Ripard wrote:
> > On Fri, Apr 17, 2015 at 04:40:43PM +0200, Gregory CLEMENT wrote:
> >> Hi Maxime,
> >>
> >> On 17/04/2015 16:32, Maxime Ripard wrote:
> >>> On Fri, Apr 17, 2015 at 04:19:22PM +0200, Boris Brezillon wrote:
> >>>> Hi Gregory,
> >>>>
> >>>> On Fri, 17 Apr 2015 15:01:01 +0200
> >>>> Gregory CLEMENT <gregory.clement@...e-electrons.com> wrote:
> >>>>
> >>>>> Hi Boris,
> >>>>>
> >>>>> On 17/04/2015 10:39, Boris Brezillon wrote:
> >>>>>> On Fri, 17 Apr 2015 10:33:56 +0200
> >>>>>> Boris Brezillon <boris.brezillon@...e-electrons.com> wrote:
> >>>>>>
> >>>>>>> Hi Jason,
> >>>>>>>
> >>>>>>> On Mon, 13 Apr 2015 20:11:46 +0000
> >>>>>>> Jason Cooper <jason@...edaemon.net> wrote:
> >>>>>>>
> >>>>>>>>>
> >>>>>>>>>> I'd appreciate if we'd look into it.  I understand from on-list and
> >>>>>>>>>> off-list discussion that the rewrite was unavoidable.  So I'm willing to
> >>>>>>>>>> concede that.  Giving people time to migrate from old to new while still
> >>>>>>>>>> being able to update for other security fixes seems reasonable.
> >>>>>>>>>
> >>>>>>>>> Jason, what do you think of the approach above? 
> >>>>>>>>
> >>>>>>>> I say keep it simple.  We shouldn't use the DT changes to trigger one
> >>>>>>>> vice the other.  We need to be able to build both, but only load one at
> >>>>>>>> a time.  If that's anything other than simple to do, then we make it a
> >>>>>>>> Kconfig binary choice and move on.
> >>>>>>>
> >>>>>>> Actually I was planning to handle it with a Kconfig dependency rule
> >>>>>>> (NEW_DRIVER depends on !OLD_DRIVER and OLD_DRIVER depends
> >>>>>>> on !NEW_DRIVER).
> >>>>>>> I don't know how to make it a runtime check without adding new
> >>>>>>> compatible strings for the kirkwood, dove and orion platforms, and I'm
> >>>>>>> sure sure this is a good idea.
> >>>>>>   ^ not
> >>>>>>
> >>>>>>> Do you have any ideas ?
> >>>>>
> >>>>> You use devm_ioremap_resource() in the new driver, so if the old one
> >>>>> is already loaded the memory region will be already hold and the new
> >>>>> driver will simply fail during the probe. So for this part it is OK.
> >>>>
> >>>> I like the idea :-).
> >>>
> >>> Not really, how do you know which device is going to be probed? For
> >>> that matter, it's pretty much random, and you have no control over it.
> >>>
> >>> Why not just have a choice option, and select which one you want to
> >>> enable?
> >>
> >> Because you can't prevent an user to build a module, then modifying the
> >> configuration and building the other module.
> > 
> > Well, actually, you don't even know if it's going to be a module. You
> > might very well have both drivers compiled statically in the kernel
> > image, and this is where the trouble begins.
> 
> No it won't be possible, Boris already speak about this issue (see below):
> "Actually I was planning to handle it with a Kconfig dependency rule
> (NEW_DRIVER depends on !OLD_DRIVER and OLD_DRIVER depends
> on !NEW_DRIVER)."

Which is a circular dependency and won't work.

> >> So even if there is a choice at build time, and I think that it is
> >> something expected for the v2, we still need preventing having the
> >> both drivers trying accessing the same hardware in the same time.
> > 
> > Of course, but this is already there, and doesn't really address the
> > same issue.
> 
> This was the only issue remaining, (see below again):
> "I don't know how to make it a runtime check ". And my last emails
> was bout it.

Ok, my bad then :)

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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