Re: [PATCH v3 09/11] hwmon: (amc6821) Convert to use regmap

From: Quentin Schulz
Date: Mon Jul 08 2024 - 06:38:17 EST


Hi Guenter,

On 7/5/24 4:28 PM, Guenter Roeck wrote:
On 7/5/24 03:59, Quentin Schulz wrote:
Hi Guenter,

On 7/4/24 7:52 PM, Guenter Roeck wrote:
[...]
+    err = regmap_read(regmap,
+              channel ? AMC6821_REG_RTEMP_FAN_CTRL : AMC6821_REG_LTEMP_FAN_CTRL,
+              &regval);
+    if (err)
+      return err;
+    temps[1] = (regval & 0xF8) >> 1;

I think we want to use AMC6821_TEMP_LIMIT_MASK here instead of 0xF8?

I guess we could also use FIELD_GET?


Yes. The value in the register is in °C * 4, so that is going to be
    temps[1] = FIELD_GET(regval, AMC6821_TEMP_LIMIT_MASK) * 4;
which improves readability and should also clarify the units a bit
better.

Note hat
    (regval & 0xF8) >> 1;
resulted in the temperature in °C (shift right 1 instead of 3).


Yes, it actually took me a while to figure out why this 1b shift was necessary as it didn't match what I got from the datasheet, but the formula was actually (>>3) * 4. Former because the register starts at bit 3, so we need to right-shift by three bits to have the actual value. Then multiply by 4 because a bit in the register means 4°C.

So yes, much more readable with this instead :)

[...]

+        /*
+         * Passive cooling temperature. Range limit against low limit
+         * of both channels.
+         */
+        val = DIV_ROUND_CLOSEST(clamp_val(val, 0, 63000), 1000);

This was already in the original code, but I think 64°C should be doable as well? The datasheet says:

"""
The PSV ranges from 0°C to +64°C.
"""


Yes, but I am sure the datasheet is wrong here. The register has 6 active bits,
which means the highest possible value is 0x3f or 63.

And there's a PSV8 bit we can write, meaning we can do (1 << 8) with a step of 4°C which gives us 64°C? In a separate commit though, to not mix too many fixes into one, making it easier for people to identify and possibly revert them if necessary.

Not sure I understand. Can you clarify ?

Temperature bit assignments in the datasheet are confusing. PSV3
means full degrees C, PSV8 means 32 degrees C. That is all in one register.
On the other side, L-TEMP0 reflects _4_ degrees C.

Am I missing something ?


No, my brain came up with its own math. Register value TEMPERATURE MONITORING section all seems to be 1°C increments (except Temp-DATA-LByte since it represents 0.125°C increments for a few select registers.

Thanks for taking the time to explain!
Quentin