linux-kernel - Re: [PATCH] iio: accel: kx022a: Improve reset delay

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Message-ID: <be375e24f74997743743fadf68125e176c23e2df.camel@gmail.com>
Date: Thu, 14 Nov 2024 10:43:05 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Matti Vaittinen <mazziesaccount@...il.com>, Matti Vaittinen
	 <matti.vaittinen@...rohmeurope.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen
 <lars@...afoo.de>, 	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: accel: kx022a: Improve reset delay

On Thu, 2024-11-14 at 08:57 +0200, Matti Vaittinen wrote:
> All the sensors supported by kx022a driver seemed to require some delay
> after software reset to be operational again. More or less a random
> msleep(1) was added to cause the driver to go to sleep so the sensor has
> time to become operational again.
> 
> Now we have official docuumentation available:
> https://fscdn.rohm.com/kionix/en/document/AN010_KX022ACR-Z_Power-on_Procedure_E.pdf
> https://fscdn.rohm.com/kionix/en/document/TN027-Power-On-Procedure.pdf
> https://fscdn.rohm.com/kionix/en/document/AN011_KX134ACR-LBZ_Power-on_Procedure_E.pdf
> 
> stating the required time is 2 ms.
> 
> Due to the nature of the current msleep implementation, the msleep(1) is
> likely to be sleeping more than 2ms already - but the value "1" is
> misleading in case someone needs to optimize the start time and change
> the msleep to a more accurate delay. Hence it is better for
> "documentation" purposes to use value which actually reflects the
> specified 2ms wait time.
> 
> Change the value of delay after software reset to match the
> specifications and add links to the power-on procedure specifications.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> ---
> Sorry for not including this to the KX134ACR-LBZ series I sent
> yesterday. It was only half an hour after I had sent the KX134ACR-LBZ
> support when I was notified about the existence of the KX022ACR-Z
> start-up procedure specification... Hence this lone patch to code which
> I just sent a miscallaneous series for before.
> 
>  drivers/iio/accel/kionix-kx022a.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-
> kx022a.c
> index 32387819995d..ccabe2e3b130 100644
> --- a/drivers/iio/accel/kionix-kx022a.c
> +++ b/drivers/iio/accel/kionix-kx022a.c
> @@ -1121,10 +1121,15 @@ static int kx022a_chip_init(struct kx022a_data *data)
>  		return ret;
>  
>  	/*
> -	 * I've seen I2C read failures if we poll too fast after the sensor
> -	 * reset. Slight delay gives I2C block the time to recover.
> +	 * According to the power-on procedure documents, there is (at least)
> +	 * 2ms delay required after the software reset. This should be same
> for
> +	 * all, KX022ACR-Z, KX132-1211, KX132ACR-LBZ and KX134ACR-LBZ.
> +	 *
> +	 *
> https://fscdn.rohm.com/kionix/en/document/AN010_KX022ACR-Z_Power-on_Procedure_E.pdf
> +	 *
> https://fscdn.rohm.com/kionix/en/document/TN027-Power-On-Procedure.pdf
> +	 *
> https://fscdn.rohm.com/kionix/en/document/AN011_KX134ACR-LBZ_Power-on_Procedure_E.pdf
>  	 */
> -	msleep(1);
> +	msleep(2);

msleep() is not advisable for something lower than 20ms. Maybe take the
opportunity and change it to fsleep()?

- Nuno Sá