linux-kernel - Re: [PATCH] counter: ti-eqep: implement over/underflow events

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Date: Sat, 15 Jun 2024 11:30:59 -0500
From: David Lechner <dlechner@...libre.com>
To: William Breathitt Gray <wbg@...nel.org>
Cc: Judith Mendez <jm@...com>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] counter: ti-eqep: implement over/underflow events

On 6/15/24 2:01 AM, William Breathitt Gray wrote:
> On Sun, Jun 09, 2024 at 04:49:33PM -0500, David Lechner wrote:
>> This adds support to the TI eQEP counter driver for subscribing to
>> overflow and underflow events using the counter chrdev interface.
>>
>> Signed-off-by: David Lechner <dlechner@...libre.com>
>> ---
>> This is split out from a series that was sent a few years back [1] that
>> I never finished, so I'm calling it v2. This was tested on a BeagleBone
>> Blue using LEGO MINDSTORMS EV3 motors and this script[2].
>>
>> [1]: https://lore.kernel.org/linux-iio/20211017013343.3385923-2-david@lechnology.com/
>> [2]: https://github.com/dlech/linux-counter-ti-eqep-python/blob/3745b0840736248d8e60cc675a0f43558fcbb2af/test.py
>>
>> v2 changes:
>> * Only clear interrupts that were handled.
>> * Don't set default QPOSMAX value.
>> * Don't error when setting QPOSMAX to 0.
>> * Use regmap_write() when appropriate.
>> * Validate watch channel.
>> * Use counter_priv().
> 
> Hi David,
> 
> It's nice to see progress on this again. I remember there being some
> sort of interrupt storm if QPOSMAX was set to 0. Is that still the case,
> or was it resolved with the changes in this version?
> 
> Willia Breathitt Gray

I haven't tried it with the rest of the old series yet, but with this
patch, it is not a problem to set QPOSMAX (ceiling) to 0.