linux-kernel - Re: [PATCH v2 3/7] mfd: pm8921: Migrate to irqdomains

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Message-ID: <20140108081452.GC19974@lee--X1>
Date:	Wed, 8 Jan 2014 08:14:52 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/7] mfd: pm8921: Migrate to irqdomains

On Tue, 07 Jan 2014, Stephen Boyd wrote:

> On 01/07, Lee Jones wrote:
> > > >> +	return of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);
> > > >> +}
> > > > Can't you use the MFD core instead?
> > > >
> > > 
> > > Are you suggesting using mfd_add_devices()? At first glance it looks
> > > like that would require an array of mfd_cell structures that do nothing
> > > besides match compatible strings in the DT. Using of_platform_populate()
> > > achieves the same goal and doesn't require an array of mfd_cell
> > > structures for each different pm8xxx chip that comes along, meaning
> > > simpler code.
> > 
> > I'm inclined to agree, but playing Devil's advocate here, as a device
> > using the MFD subsystem it's often clearer to readers and other people
> > looking for examples if the MFD core functionality is used. For
> > instance, I now have no idea what devices the PM8xxx encompasses
> > without looking at the DTS file. A small cell structure is a small
> > price to pay for code clarity IMHO.
> > 
> 
> Why not just put that information in the binding document? And
> how is this different from adding a bunch of C files to match a
> set of compatible strings that a dts file has just so that we can
> add all the devices on a board (think board files for an SoC).
> Sure it documents the devices on a board, but we've been moving
> away from that by using of_platform_populate().
> 
> IMHO the code is clear. I want to add all subnodes of this
> device's node as children struct devices. Using
> of_platform_populate() says that, whereas mfd_add_devices() says
> I want to add these specific subnodes of this device's node.
> 
> Also, as more drivers are written and more bindings are ratified
> this platform driver will need to be updated with more cells and
> more compatible strings, causing more inter-tree dependencies and
> more patches. Please, let's avoid this if we can.

Okay, that's fine. There are a few discussions floating around about
this. If I find some time, I'll have to have a think about the pros
and cons of either approach. This is okay for now.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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