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

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Message-ID: <CANEuBv5uTBurgpoXBh143T0sB+GCj8oymDxh5+2CqXk5A4dYqw@mail.gmail.com>
Date:   Tue, 18 Apr 2017 17:15:47 -0700
From:   Markus Mayer <code@...yer.net>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        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

On 18 April 2017 at 15:47, Guenter Roeck <linux@...ck-us.net> wrote:
> 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 for the tip. As Florian said, it was not the idea to submit a
completely non-standard hwmon driver. I was sure I would be able to
report at least some standard hwmon data also.

Regards,
-Markus