linux-kernel - Re: [PATCH v2] hwmon: Add driver for AMD family 15h processor power information

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Date:	Wed, 06 Apr 2011 09:14:07 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Guenter Roeck <guenter.roeck@...csson.com>,
	Andreas Herrmann <herrmann.der.user@...glemail.com>
CC:	Jean Delvare <khali@...ux-fr.org>,
	Thomas Renninger <trenn@...e.de>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] hwmon: Add driver for AMD family 15h processor power
 information

Guenter Roeck wrote:
> On Tue, Apr 05, 2011 at 10:45:36AM -0400, Andreas Herrmann wrote:
> > +static int __devinit f15h_power_is_internal_node0(struct pci_dev *f4)
> > +{
> > +	u32 val;
> > +	struct pci_dev *f3;
> > +
> > +	f3 = pci_get_slot(f4->bus, PCI_DEVFN(PCI_SLOT(f4->devfn), 3));
> > +	if (!f3) {
> > +		dev_err(&f4->dev, "no function 3 available on this slot\n");
> > +		return 0;
> 
> It is a common practice to return a negative value on errors. Why not here ?

Apparently, this function returns a boolean value.  Using "bool"/"true"/
"false" would have made this more obvious.

> Also, is this really an error which asks for an error message, or just a CPU
> or system which does not support the attribute ?

AFAICT all F15h CPUs are _known_ to have all these PCI functions; the
error should never occur in practice.

What I do in the k10temp driver in this situation is to trust the CPU to
be there, omitting the pci_get_slot/pci_dev_put and just replacing this:

> > +	pci_read_config_dword(f3, REG_NORTHBRIDGE_CAP, &val);
> > +	pci_dev_put(f3);

with the equivalent of:

  pci_bus_read_config_dword(f4->bus, PCI_DEVFN(PCI_SLOT(f4->devfn), 3),
                            REG_NORTHBRIDGE_CAP, &val);


BTW: The family 15h CPUs have the same temperature sensor registers
(D18F3xA4 and D18F3x64) as the earlier families, haven't they?


Regards,
Clemens
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