From mboxrd@z Thu Jan  1 00:00:00 1970
From: benh@kernel.crashing.org (Benjamin Herrenschmidt)
Date: Thu, 08 Aug 2013 08:42:24 +1000
Subject: [PATCHv7 07/13] irqdomain: add function to find a MSI irq_domain
In-Reply-To: <1375914665.12551.5.camel@pasglop>
References: <1375867954-2320-1-git-send-email-thomas.petazzoni@free-electrons.com>
 <1375867954-2320-8-git-send-email-thomas.petazzoni@free-electrons.com>
 <1375908620.9300.3.camel@pasglop> <20130808000443.17f57875@skate>
 <1375914665.12551.5.camel@pasglop>
Message-ID: <1375915344.12551.6.camel@pasglop>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, 2013-08-08 at 08:31 +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2013-08-08 at 00:04 +0200, Thomas Petazzoni wrote:
> > Again, this has been discussed at lengths in the previous iterations,
> > for which I already gave you all the links, as you requested in a
> > private e-mail. It'd be great if this discussion was read seriously,
> > because I really have the feeling we are restarting from zero on this
> > whole MSI thing...
> 
> Well, two things here:
> 
>  - You don't need my ack since I am not the maintainer of the irqdomain
> code anymore, Grant is :-)

Hrm, I'm being told Grant isn't anymore... I can step in and take it all
back but you might not like the result ....

Ben.

>  - I still don't like it. I find that it's looking more and more like
> over engineering. I don't like having any kind of infrastructure
> relationship between MSI stuff and irqdomain, ie, a PCI/PCIe specific
> construct and a generic interrupt remapper.
> 
> Trying to use irqdomain for HW number allocation seems to be pushing it
> where it wasn't designed to go. Are those interrupts really different
> domains ? Do they have separate number spaces, separate DT encodings and
> overall characteristics ?
> 
> What's wrong with the bitmap allocator in the PIC driver ? It's simple,
> and does the job just fine. If anything, take it from powerpc and sparc
> and move it to generic. It's already a "generic" (ie shared)
> infrastructure in powerpc.
> 
> Let's ask somebody of well known taste ... Thomas ! :-) (Yes, you tglx,
> I know you are lurking ...). What do you reckon ?
> 
> That series makes me feel nervous, it feels like a hack. I really don't
> like creating that relationship between msi_chip and irqdomain. In fact,
> I think it makes it harder to understand what's happening in the code
> and following things.
> 
> It's a LOT clearer to me to have an irq domain for the PIC and an
> explicit bitmap allocation for MSIs, I see where things come from, I can
> follow the code path etc... much more easily.
> 
> I suspect we have a case of over-abstracting happening here. This is a
> dangerous illness and can be contagious :-)
> 
> Cheers,
> Ben.
>