Message-ID: <20120123155408.7d52e4da@v0nbox>
Date:	Mon, 23 Jan 2012 15:54:08 -0500
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	"x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/platform: (TS-5500) revised ADC driver

On Sun, 22 Jan 2012 20:36:46 -0800,
Guenter Roeck <guenter.roeck@...csson.com> wrote: 
> > > Regarding the location, I'd really like to know from the
> > > powers-that-be if arch/x86/platform/ts5500/
> > > or
> > > 	drivers/platform/x86
> > > or
> > > 	drivers/hwmon
> > > 
> > > would be the appropriate location for a driver like this. As
> > > mentioned before, my strong preference is drivers/hwmon, but I
> > > would like to hear from others.
> > 
> > We should either split every driver into corresponding
> > subdirectories, or put everything in a common platform directory.
> > My first RFC patches set has every driver separated. As they are
> > really specific to the platform, people seem to agree with grouping
> > them, mainly because they won't be shared. I changed that in the
> > following patches sets, and X86 maintainers seemed to be ok with
> > that.
> > 
> > I'm ok with both solutions, but we should all agree on one.
> > Maybe we should have other maintainers view on this?
> > 
> That is what I had asked for. I thought the whole point of per-module 
> directories was to have all drivers there. If that is no longer true,
> fine with me; who am I to argue about something like that.
> I'd just like to know.
> 
> > > Also, I am not sure if the current approach is appropriate to
> > > start with. Looking at the datasheet as well as into existing
> > > kernel code, it appears quite likely that some kind of more or
> > > less generic MAX197 driver exists somewhere. The existence of
> > > is_max197_installed() - without any calling code - is a strong
> > > indication that this is the case, as well as the "static"
> > > platform data in your original patch. It might be more
> > > appropriate to take this more or less generic driver, move it to
> > > drivers/hwmon, and provide - for example through platform data -
> > > a means to read from and write to the chip on a per-platform
> > > basis, ie with per-platform access functions.
> > 
> > You're right, it should be possible to create a generic max197
> > driver and provide read/write functions through platform data. But
> > we don't have a max197 right now... So it can stay as a compact
> > TS-5500 ADC driver for the moment, and maybe we will split later.
> > What do you think?
> > 
> I am lost. If you don't have a TS-5500 with max197, how do you test
> the driver ?

Sorry, I wasn't clear. I meant the only max197 I have is the one
behind the TS-5500 CPLD, I don't have any others to test independently.

> I had another look into the MAX197 and TS-5500 data sheets. In my
> opinion, a generic MAX197 driver in drivers/hwmon combined with a
> platform driver in the current location would be the way to go. That
> driver would then also work for the other TS-5x00 systems. All you
> need is a single chip access function in the platform code, since the
> chip is always accessed with a write followed by a read.

I took a deeper look at the datasheets, and you're right, a MAX197
driver seems to be a good choice. However, there are a number of
differences between a direct usage of a MAX197 and the TS-5500 mapped
MAX197.

To start a conversion of a channel for a given range and polarity, it
consists on both sides of a u8 outb() call on pins 7-14 (i.e. bits
D7-D0). To be notified when the result is ready, we can either set an
IRQ on INT pin (falling edge), or poll it.
Then on the MAX197, you read the pins 7-14, set pin HBEN to 1, and
read the same pins again to get the 4 remaining bits. On the TS-5500,
only polling is available, and the 12 bits are mapped on 2 registers.

I propose to write a max197 driver with default read and write
functions. A platform_data will be used to specify the base address
(pins 7-14), and eventually a custom read function pointer, which will
be used instead of the default one if it is different of NULL.

What do you think?

I will write a max197 driver with default read and write functions. A
platform_data will be used to specify the base address (pins 7-14), and
eventually a custom read function pointer, which will be used instead
of the default, if it is not NULL.

What do you think? 


-- 
Vivien Didelot
Savoir-faire Linux Inc.
Tel: (514) 276-5468 #149
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