linux-kernel - Re: [PATCH v6 2/2] staging: ion: create one device entry per heap

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Date:   Thu, 2 Nov 2017 11:10:19 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        sumit.semwal@...aro.org, arve@...roid.com, riandrews@...roid.com,
        dan.carpenter@...cle.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v6 2/2] staging: ion: create one device entry per heap

On Thu, Nov 02, 2017 at 11:44:07AM +0100, Greg KH wrote:
> On Tue, Oct 31, 2017 at 07:11:53PM +0000, Mark Brown wrote:

> > There was a discussion a while ago in the context of I2C/SPI MFDs
> > which concluded that if you need a bus and it's going to be effectively
> > noop then you should just use the platform bus as anything else will
> > consist almost entirely of cut'n'paste from the platform bus with some
> > light sed usage and code duplication is bad.  It's not super lovely as
> > it's not actually a memory mapped device but it's the best idea we've
> > got.

> Ugh, I hate that.  What's wrong with using a "virtual" device instead?

It was the duplication, initially everyone was making buses.  

> I can create a "virtual" bus for things like this if they really want a
> "simple" bus, abusing platform for this is the major reason I hate the
> platform bus code...

In the MFD case they're physical devices, they're just usually on the
wrong side of an I2C or SPI link.  Plus MFD already handles platform
devices for things that are memory mapped so it's a bit of a more
natural fit there.

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