linux-kernel - Re: [PATCH RFC 3/6] iio: adc: dln2-adc: make use of iio_is_soft_ts

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Message-ID: <20241130140255.70b4b68b@jic23-huawei>
Date: Sat, 30 Nov 2024 14:02:55 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Vasileios Amoiridis <vassilisamir@...il.com>
Cc: lars@...afoo.de, krzysztof.kozlowski@...aro.org, nuno.sa@...log.com,
 u.kleine-koenig@...libre.com, abhashkumarjha123@...il.com,
 jstephan@...libre.com, dlechner@...libre.com, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jack Andersen <jackoalan@...il.com>
Subject: Re: [PATCH RFC 3/6] iio: adc: dln2-adc: make use of
 iio_is_soft_ts_enabled()

On Sat, 30 Nov 2024 01:27:07 +0100
Vasileios Amoiridis <vassilisamir@...il.com> wrote:

> Use the iio_is_soft_ts_enabled() accessor to access the value of the
> scan_timestamp. This way, it can be marked as __private when there
> are no direct accessors of it.
> 
> Signed-off-by: Vasileios Amoiridis <vassilisamir@...il.com>

The original code looks to me like a micro optimization that we should
consider dropping to reduce complexity.  It is only used to zero a hole
in a structure conditionally if the timestamp is enabled.

Better I think to just drop all the ts_pad_offset etc stuff in favour of
just zeroing the whole of the data structure in dln2_adc_trigger_h()
whether or not the timestamp is enabled.

My guess is that on a reasonably performance CPU the occasional cost
of a branch miss prediction will outweigh zeroing a fairly small structure
anyway.

+CC Jack who wrote this driver.

Jonathan


> ---
>  drivers/iio/adc/dln2-adc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/dln2-adc.c b/drivers/iio/adc/dln2-adc.c
> index 30328626d9be..f9cf132c41e6 100644
> --- a/drivers/iio/adc/dln2-adc.c
> +++ b/drivers/iio/adc/dln2-adc.c
> @@ -128,7 +128,7 @@ static void dln2_adc_update_demux(struct dln2_adc *dln2)
>  		in_loc += 2;
>  	}
>  
> -	if (indio_dev->scan_timestamp) {
> +	if (iio_is_soft_ts_enabled(indio_dev)) {
>  		size_t ts_offset = indio_dev->scan_bytes / sizeof(int64_t) - 1;
>  
>  		dln2->ts_pad_offset = out_loc;