linux-kernel - Re: [PATCH/RFC] hwmon: Add support for W83667HG-B

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Date:	Fri, 2 Jul 2010 11:49:49 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Guenter Roeck <guenter.roeck@...csson.com>
Cc:	Jim Cromie <jim.cromie@...il.com>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ethan Lawrence <e.law87@...oo.com>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"lars4910@...mail.com" <lars4910@...mail.com>,
	"birdie@...monline.ru" <birdie@...monline.ru>,
	"jadcock@....net" <jadcock@....net>
Subject: Re: [PATCH/RFC] hwmon: Add support for W83667HG-B

Hi Guenter,

On Fri, 2 Jul 2010 01:25:30 -0700, Guenter Roeck wrote:
> On Fri, Jul 02, 2010 at 03:20:11AM -0400, Jean Delvare wrote:
> > On Thu, 1 Jul 2010 15:02:15 -0700, Guenter Roeck wrote:
> > > -static const u8 W83627EHF_REG_FAN_MAX_OUTPUT[] = { 0xff, 0x67, 0xff, 0x69 };
> > > -static const u8 W83627EHF_REG_FAN_STEP_OUTPUT[] = { 0xff, 0x68, 0xff, 0x6a };
> > > +
> > > +static const u8 *W83627EHF_REG_FAN_MAX_OUTPUT;
> > > +static const u8 *W83627EHF_REG_FAN_STEP_OUTPUT;
> > > +
> > > +static const u8 W83627EHF_REG_FAN_MAX_OUTPUT_COMMON[]
> > > +						= { 0xff, 0x67, 0xff, 0x69 };
> > > +static const u8 W83627EHF_REG_FAN_STEP_OUTPUT_COMMON[]
> > > +						= { 0xff, 0x68, 0xff, 0x6a };
> > > +
> > > +static const u8 W83627EHF_REG_FAN_MAX_OUTPUT_W83667_B[] = { 0x67, 0x69, 0x6b };
> > > +static const u8 W83627EHF_REG_FAN_STEP_OUTPUT_W83667_B[] = { 0x68, 0x6a, 0x6c };
> > 
> > Is it just me or these arrays aren't used anywhere?
> > 
> > I think I would just drop them. The "0xff" are suspicious in the
> > original arrays, and the size difference between the common and
> > W83667HG-B cases is tricky. Anyone willing to add support for this
> > feature will need to read the datasheets anyway, so you don't add any
> > value by including the register addresses here.
> 
> After removing the defines and trying to compile I remembered.
> I _knew_ there was a reason for not removing them.
> Guess it's too late (or early) here to do serious work.
> 
> The defines _are_ used, in:
> 
> fan_functions(fan_max_output, FAN_MAX_OUTPUT)
> fan_functions(fan_step_output, FAN_STEP_OUTPUT)
> 
> which expands to W83627EHF_REG_FAN_MAX_OUTPUT and W83627EHF_REG_FAN_STEP_OUTPUT.
> 
> Tricky ... and that was also the reason why I retained the original 
> global variables.

Tricky indeed. We normally don't accept code like this in the kernel.

> I'll move the pointers into per-device code as you suggested, but I'll
> have to think about how to do that w/o having to change a lot of code.

If code changes are desirable, let's just do them. You can do that in a
preliminary patch, and then your patch adding support for the
W83667HG-B goes on top of it.

> As for the 0xff - that pretty much applies to all chips supported by this driver. 
> I guess it is supposed to mean "not supported", and as a result the code will
> write to a non-existing register. I don't really want to touch that.

I want you to touch that. Writing to non-existing registers is a bad
idea. You never know what actually happens when you do that.

> The size difference (3 entries vs. 4) doesn't matter, since the chips are both 
> configured to have only three pwm fan controllers (even though the W83667HG
> is supposed to have four per its datasheet). So the 4th element of the arrays
> will not be accessed by the code if W83667HG(-B) is detected.

OK.

-- 
Jean Delvare
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