linux-kernel - Re: [PATCH 2/2] hwmon: (brcmstb) Add driver for Broadcom STB DPFE

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Date:   Tue, 18 Apr 2017 15:47:39 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Markus Mayer <code@...yer.net>, Jean Delvare <jdelvare@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Markus Mayer <mmayer@...adcom.com>,
        Broadcom Kernel List <bcm-kernel-feedback-list@...adcom.com>,
        Linux HWMON List <linux-hwmon@...r.kernel.org>,
        Device Tree List <devicetree@...r.kernel.org>,
        ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] hwmon: (brcmstb) Add driver for Broadcom STB DPFE

Hi Florian,

On Tue, Apr 18, 2017 at 03:29:55PM -0700, Florian Fainelli wrote:
> Hey Guenter,
> 
> On 04/18/2017 01:58 PM, Guenter Roeck wrote:
> > Hi Markus,
> > 
> > On Tue, Apr 18, 2017 at 01:17:02PM -0700, Markus Mayer wrote:
> >> From: Markus Mayer <mmayer@...adcom.com>
> >>
> >> This driver allows access to DRAM properties, such as the refresh rate,
> >> via the Broadcom STB DDR PHY Front End (DPFE). The refresh rate can be
> >> used as indirect indicator of the DRAM temperature.
> >>
> >> The driver also allows setting of the sampling interval.
> >>
> >> Signed-off-by: Markus Mayer <mmayer@...adcom.com>
> >> ---
> > [ ... ]
> > 
> >> +
> >> +static SENSOR_DEVICE_ATTR(dpfe_info, 0444, show_info, NULL, 1000);
> >> +static SENSOR_DEVICE_ATTR(dpfe_refresh, 0644, show_refresh, store_refresh,
> >> +			  1000);
> >> +static SENSOR_DEVICE_ATTR(dpfe_vendor, 0444, show_vendor, NULL, 1000);
> >> +static struct attribute *dpfe_attrs[] = {
> >> +	&sensor_dev_attr_dpfe_info.dev_attr.attr,
> >> +	&sensor_dev_attr_dpfe_refresh.dev_attr.attr,
> >> +	&sensor_dev_attr_dpfe_vendor.dev_attr.attr,
> >> +	NULL
> >> +};
> >> +ATTRIBUTE_GROUPS(dpfe);
> >> +
> > 
> > There is not a single standard hwmon attribute. I don't know how
> > to classify this driver, and where it should reside, but it is not
> > a hwmon driver. 
> 
> This is a driver that talks to an embedded CPU running firmware which is
> capable of giving various informations about the DRAM chip being
> populated, including a temperature trend (hotter or cooler). We thought
> initially we would be able to expose the actual temperature, but this in
> turn required a lot more knowledge about the DRAM chip that we wish we
> knew about. That is sort of where and why this driver was proposed for
> hwmon.
> 
> Which subsystem do you think would be best for this driver drivers/misc/
> or drivers/soc/bcm/brcmstb/ maybe?

Both should work. I would probably try misc first and let Greg tell me
which way to go ;-).

Thanks,
Guenter