Message-ID: <1327440010.2649.204.camel@groeck-laptop>
Date:	Tue, 24 Jan 2012 13:20:10 -0800
From:	Guenter Roeck <guenter.roeck@...csson.com>
To:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
CC:	"khali@...ux-fr.org" <khali@...ux-fr.org>,
	"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>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>
Subject: Re: [PATCH] x86/platform: (TS-5500) revised ADC driver

On Tue, 2012-01-24 at 15:16 -0500, Vivien Didelot wrote:
> Le Mon, 23 Jan 2012 16:41:38 -0800,
> Guenter Roeck <guenter.roeck@...csson.com> a écrit :
> 
> > On Mon, Jan 23, 2012 at 05:35:51PM -0500, Vivien Didelot wrote:
> > > On Mon, 23 Jan 2012 15:54:08 -0500,
> > > Vivien Didelot <vivien.didelot@...oirfairelinux.com> wrote:
> > > 
> > > > 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? 
> > > 
> > Sounds like a plan to me.
> > 
> > > Sorry for the duplicate :)
> > > 
> > > BTW, I've added Jean Delvare and the lm-sensors mailing list in Cc,
> > > in case they have an opinion on this.
> > > 
> > 
> > Thanks,
> > Guenter
> 
> Hi Guenter,
> 
> There's another disadvantage with the generic driver.
> Usually, the MAX197 is memory mapped, but on the TS-5500, the CPLD is
> port mapped, so even the write function would be different.
> It sounds like the amount of reusable lines of code is not that
> significant.
> 
> Do you think it is still worthwhile?

Points to a platform specific access function, as I had suggested
earlier. The access function is just a small part of the driver; the
entire hwmon/sysfs code is generic. Yes, I think it is worthwhile.

Guenter


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