From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Wed, 7 Aug 2013 02:52:14 +0100 Subject: [Ksummit-2013-discuss] [ARM ATTEND] Describing complex, non-probable system topologies In-Reply-To: References: <20130801183531.GB29831@mudshark.cambridge.arm.com> <20130801192730.GC9174@kroah.com> <20130802115334.GN2465@mudshark.cambridge.arm.com> <20130802142010.GC7533@kroah.com> <20130802160932.GG5292@mudshark.cambridge.arm.com> <20130802223247.GC28831@kroah.com> Message-ID: <20130807015214.GH15579@mudshark.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sat, Aug 03, 2013 at 06:16:57AM +0100, Olof Johansson wrote: > On Fri, Aug 2, 2013 at 3:32 PM, Greg KH wrote: > > I don't scale if I'm forced to review every driver to ensure that they > > shouldn't be using platform device and should be creating their own bus > > type. You can do that, along with the other ARM developers reviewing > > these new subsystems and code being added. > > For most new platforms, using basic platform_bus devices makes sense > when the setup is simple and just has a few devices. It's only when > they need to add support for {S,IO}MMUs and get the more advanced > functionality going that things get messy and platform_bus stops > working. Right, but being more forward-looking, we will need to know this kind of topological information to do simple things like (coherent) DMA or even just to generate/route an interrupt. > So, we have the option of having someone care about the {S,IO}MMU > pieces, and when they spot the attempts to make that work, push them > towards a proper bus architecture. Until then, the simpler solution is > probably a reasonable idea compared to having newcomers worry about > defining new bus architectures and raising the bar for what it takes > to sort out the initial contributions and getting engaged upstream. I take your point, but at the same time we don't want to find ourselves suddenly landed with having to convert a bunch of drivers to sit on different buses as an afterthought. There's likely some middle-ground that is difficult to envisage up-front. Will