linux-kernel - Re: [PATCH v6 0/8] mfd: introduce a driver for LPSS devices on SPT

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Date:	Mon, 27 Jul 2015 23:48:54 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	mturquette@...libre.com, sboyd@...eaurora.org
Subject: Re: [PATCH v6 0/8] mfd: introduce a driver for LPSS devices on SPT

On Monday, July 27, 2015 05:24:13 PM Lee Jones wrote:
> On Mon, 27 Jul 2015, Mika Westerberg wrote:
> 
> > On Mon, Jul 27, 2015 at 04:27:33PM +0100, Lee Jones wrote:
> > > FAO Stephen Boyd,
> > > 
> > > > Stephen, can you, please, have a look into patch 8 regarding to clock name
> > > > matching and other stuff Lee asked?
> > > 
> > > Patch 8:
> > > 
> > >       "Can you review the clock implementation please?  It looks
> > >       fragile to me as it relies heavily on device names constructed
> > >       of MFD cell names and IDA numbers cat'ed together!"
> > 
> > Lee, can you suggest an alternative then?
> > 
> > Why we are doing it like this is that number of different LPSS devices
> > changes from SoC to SoC. In addition to that the device (called "slice")
> > might have iDMA block or not.
> > 
> > Since the drivers in question (pxa2xx-spi, i2c-designware and 8250_dw)
> > use standard clk framework to request their clocks the Linux device must
> > have clock registered which matches the device in advance.
> > 
> > Because we add the host controller device dynamically (from the MFD
> > driver) based on how many devices are actually present, we need somehow
> > predict what would be the correct name and instance number for that
> > device to get the clock for it. That's the reason we use IDA here along
> > with the cell name (or driver name).
> 
> I'm sure there are perfectly viable reasons for you doing this.  And I
> don't know the CCF well enough to know whether it's the best idea or
> not, or else I would have made a suggestion rather than waiting all
> this time.
> 
> It's for this reason that I needed Mike (now Stephen) to take a look
> and give me either an Ack, to say it's the best solution, or to
> provide a better alternative.
> 
> Until that happens, I'm stuck!

Well, what if we had no one at hand to review that code?  Would that mean it
would not be applicable forever?

Thanks,
Rafael

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