On Sun, Mar 5, 2017 at 8:28 AM, Guenter Roeck [off-list ref] wrote:

On 03/01/2017 07:29 PM, Rick Altherr wrote:

quoted

Resending in plain text.

On Tue, Feb 28, 2017 at 7:45 PM, Guenter Roeck [off-list ref] wrote:

quoted

On 02/28/2017 04:49 PM, Joel Stanley wrote:

quoted

On Wed, Mar 1, 2017 at 6:44 AM, Rick Altherr [off-list ref]
wrote:

quoted

Aspeed AST2400/AST2500 BMC SoCs include a 16 channel, 10-bit ADC. This
driver implements reading the ADC values, enabling channels via device
tree, and optionally providing channel labels via device tree.  Low and
high threshold interrupts are supported by the hardware but not
implemented.

Signed-off-by: Rick Altherr <redacted>

Looks good. Some minor comments below.

Is there a reason you wrote a hwmon driver instead of an iio driver? I
wasn't sure what the recommended subsystem is.

Excellent point. Question is really if there is a plan to add support for
thresholds. If not, an iio driver might be more appropriate.

Guenter

The hardware supports firing interrupts on high and low thresholds.
I'm not planning to use that feature yet so I didn't implement it.
Would you prefer that I leave it as is (maybe with a TODO), implement
the thresholding, or change to iio?

Let's try to determine the intended use of the ADC. I don't find the
datasheet
online; all I can find is brief summaries which don't me tell much, but
suggest
that it is a general purpose ADC and not specifically intended for hardware
monitoring. What is the minimum sampling rate ? That should give us an idea.
If it is in the uS range, iio would be more appropriate (and the iio-hwmon
bridge could be used if a channel is in fact used for hardware monitoring).

Thanks,
Guenter

AST2500 is a BMC SoC from Aspeed
(https://www.aspeedtech.com/products.php?fPath=20&rId=440).  The BMC
is a separate, always-on computer that manages the health and remote
management for a server.  The driver I sent is for the ADCs included
in the SoC that are intended to monitor power rails on the server
motherboard but are really just general-purpose ADCs.  According to
the (not public) datasheet, the sampling rate is 10-500kHz, resolution
is 10-bit, and precision +/- 2%.  This is my first time writing a
linux driver for ADCs.  My cursory look at iio indicates that that
will work fine for this driver and the hwmon-iio bridge will suffice
for the userspace stack which is currently expecting hwmon APIs.