linux-kernel - Re: [PATCH] hwmon, fam15h_power: Add support for two more processors

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Date:	Wed, 10 Sep 2014 13:37:19 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
Cc:	herrmann.der.user@...glemail.com, jdelvare@...e.de,
	lm-sensors@...sensors.org, linux-kernel@...r.kernel.org,
	Boris Ostrovsky <boris.ostrovsky@....com>
Subject: Re: [PATCH] hwmon, fam15h_power: Add support for two more processors

On Wed, Sep 10, 2014 at 03:01:36PM -0500, Aravind Gopalakrishnan wrote:
> On 9/10/2014 12:53 PM, Guenter Roeck wrote:
> >On Wed, Sep 10, 2014 at 12:02:08PM -0500, Aravind Gopalakrishnan wrote:
> >>Fam16h,M30h(Mullins) and Fam15hM30h(Kaveri) processors can
> >>report 'power_crit' value. So, adding their respective device ids.
> >>
> >>Also, according to BKDGs, the 'TdpRunAvgAccCap' that show_power()
> >>uses is valid only on Fam15h, Models 0x0-0xF. On all other processors
> >>the field is 'Reserved'. So, return error if we are on any other family/model.
> >>
> >>Impact on lm-sensors is minimal. On such families, instead of reporting
> >>Current power value as '0', we now have:
> >>power1:           N/A
> >>
> >It will result in people complaining to us about it.
> >
> >It would be more appropriate to not create the attribute the first place
> >if it is not supported. Sure, that is a bit more code, but it isn't that bad.
> >You can simply return -ENODEV for unsupported CPUs from the probe function.
> >
> >
> >>Signed-off-by: Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
> >>---
> >>  drivers/hwmon/fam15h_power.c | 6 ++++++
> >>  1 file changed, 6 insertions(+)
> >>
> >>diff --git a/drivers/hwmon/fam15h_power.c b/drivers/hwmon/fam15h_power.c
> >>index 4a7cbfa..b69bf7d 100644
> >>--- a/drivers/hwmon/fam15h_power.c
> >>+++ b/drivers/hwmon/fam15h_power.c
> >>@@ -57,6 +57,10 @@ static ssize_t show_power(struct device *dev,
> >>  	struct fam15h_power_data *data = dev_get_drvdata(dev);
> >>  	struct pci_dev *f4 = data->pdev;
> >>+	/* The value TdpRunAvgAccCap is valid only on F15h, Models 0x0-0xF */
> >>+	if (boot_cpu_data.x86 != 0x15 || boot_cpu_data.x86_model > 0x0)
> >The comment does not match the code. The comment talks about accepting models
> >F15h, models 0x0-0xF, but the code rejects anything but F15h model 0x0.
> 
> Ah. Yes, The condition should have been (..boot_cpu_data.x86_model > 0xf)
> 
> >Now it may well be that the above describes identifies all F15h and F16h CPUs,
> >but this is not clear from the comment. It rather looks as if anything but F15h,
> >model 0x0 is rejected, including all F16h CPUs. But then why accept F16h CPUs
> >in the first place ?
> 
> Yes, we want to reject anything but F15h, Models 00h-0fh.
> The reason I included the newer processor IDs, (and let
> PCI_DEVICE_ID_AMD_16H_NB_F4) remain
> is because we can still obtain 'critical power value'. It is only
> the 'current power' that is not exposed.
> 
That is a behavioral change, though; previously the current power was
reported for F16h chips with PCI ID PCI_DEVICE_ID_AMD_16H_NB_F4.
Is this a bug, ie should the power value not have been reported
for the F16h chips ?

> If we return -ENODEV in the probe function (or we can just remove
> the listed PCI_DEVICE_ID), then we'd not get the critical power
> values too.
> 
If you want to make the actual power reporting conditional, you should
introduce an is_visible function to the attribute group to ensure that
power1_input is only reported if/when supported. If the actual power 
value is not really supported for F16h chips, you should actually provide
two separate patches: One to make power1_input optional, to be reported for
supported chips only, and another to add more chips. One is a bug fix,
the other a functionality extension.

Guenter

> - Aravind.
> 
> >>+		return -ENOSYS;
> >>+
> >>  	pci_bus_read_config_dword(f4->bus, PCI_DEVFN(PCI_SLOT(f4->devfn), 5),
> >>  				  REG_TDP_RUNNING_AVERAGE, &val);
> >>  	running_avg_capture = (val >> 4) & 0x3fffff;
> >>@@ -216,7 +220,9 @@ static int fam15h_power_probe(struct pci_dev *pdev,
> >>  static const struct pci_device_id fam15h_power_id_table[] = {
> >>  	{ PCI_VDEVICE(AMD, PCI_DEVICE_ID_AMD_15H_NB_F4) },
> >>+	{ PCI_VDEVICE(AMD, PCI_DEVICE_ID_AMD_15H_M30H_NB_F4) },
> >>  	{ PCI_VDEVICE(AMD, PCI_DEVICE_ID_AMD_16H_NB_F4) },
> >>+	{ PCI_VDEVICE(AMD, PCI_DEVICE_ID_AMD_16H_M30H_NB_F3) },
> >>  	{}
> >>  };
> >>  MODULE_DEVICE_TABLE(pci, fam15h_power_id_table);
> >>-- 
> >>2.0.3
> >>
> 
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