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 17:24:13 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	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 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!

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