Re: [PATCH v1] iio: adc: aspeed: Support deglitch feature.

On Tue, 17 Oct 2023 11:10:54 +0000
Billy Tsai [off-list ref] wrote:

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Create event sysfs for applying the deglitch condition. When
in_voltageY_thresh_rising_en/in_voltageY_thresh_falling_en is set to true,
the driver will use the in_voltageY_thresh_rising_value and
in_voltageY_thresh_falling_value as threshold values. If the ADC value
falls outside this threshold, the driver will wait for the ADC sampling
period and perform an additional read once to achieve the deglitching
purpose.

Signed-off-by: Billy Tsai <redacted>  

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Hi Billy  

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This is pushing the meaning of the events interface too far.
You can't use it to hide a value you don't like from userspace.  

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If you can explain what the condition is that you are seeing
and what you need to prevent happening if it is seen that would help
us figure out if there is another way to do this.  

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Jonathan  

Hi Jonathan,

Currently, we are experiencing some voltage glitches while reading from our
controller, but we do not wish to report these false alarms to the user space.
Instead, we want to retry the operation as soon as possible. This is why the
driver requires this patch to handle retries internally, rather than relying on user
space which could introduce unpredictable timing for retrying the reading process.
This software approach aims to minimize the possibility of false alarms as much as possible.  

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Thanks for the extra detail. Perhaps share more of that in the cover letter for v2.  

Okay, I will incorporate more details into my commit message for v2.
 

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If you have any suggestions or recommendations regarding this situation, please feel free to
share them with me.  

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Why do you need userspace control for the thresholds?
Perhaps this is something that belongs in DT for a particular board design?  

If the input voltage remains constant, these settings can be incorporated into the DTS properties for configuring the threshold. However, if the input voltage is subject to change, adding user-space control may offer more flexibility.  

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My concern is that it's an interface userspace probably won't know how to use, or
will misuse given this seems to be papering over bad hardware.  

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If there is a 'safe' value to put in DT I'd prefer to see that. I guess it might be per
channel thing to adjust for different expected voltage ranges?  

Yes, the voltage ranges should be adjusted based on each individual channel.
I'm not entirely sure what you mean by the term 'safe' value. 
Are you suggesting that a DTS property should be used to constrain the threshold ranges? Or someting else?
From my point of view, I think misusing this feature will only increase the sampling period of the ADC values and decrease the sensitivity.
As the name of this feature , it is primarily used to eliminate or mitigate glitches in readings.

Note a good choice of wording from me.  I meant, for a given design (and hence DTS)
is there a reasonable value that will work for all instances of that design?

If there is it is a characteristic of the board design and should be in DT.
If there isn't, how do you calibrate it for individual devices?

Jonathan

Thanks

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