linux-kernel - Re: [PATCH v2 3/4] iio: common: ssp_sensors: drop conditional optimization for simplicity

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Message-ID: <82e97712-3765-4d93-bdb5-f50fa7025e81@baylibre.com>
Date: Wed, 18 Dec 2024 09:17:44 -0600
From: David Lechner <dlechner@...libre.com>
To: Vasileios Amoiridis <vassilisamir@...il.com>
Cc: jic23@...nel.org, lars@...afoo.de, krzysztof.kozlowski@...aro.org,
 nuno.sa@...log.com, u.kleine-koenig@...libre.com,
 abhashkumarjha123@...il.com, jstephan@...libre.com, jackoalan@...il.com,
 k.wrona@...sung.com, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] iio: common: ssp_sensors: drop conditional
 optimization for simplicity

On 12/17/24 5:41 PM, Vasileios Amoiridis wrote:
> On Mon, Dec 16, 2024 at 03:57:44PM -0600, David Lechner wrote:
>> On 12/14/24 1:14 PM, Vasileios Amoiridis wrote:
>>> Drop conditional in favor of always calculating the timestamp value.
>>> This simplifies the code and allows to drop usage of internal private
>>> variable "scan_timestamp" of the struct iio_dev.
>>>
>>> Signed-off-by: Vasileios Amoiridis <vassilisamir@...il.com>
>>> ---
>>>  drivers/iio/common/ssp_sensors/ssp_iio.c | 9 +++------
>>>  1 file changed, 3 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/iio/common/ssp_sensors/ssp_iio.c b/drivers/iio/common/ssp_sensors/ssp_iio.c
>>> index caa404edd9d0..6b86b5315694 100644
>>> --- a/drivers/iio/common/ssp_sensors/ssp_iio.c
>>> +++ b/drivers/iio/common/ssp_sensors/ssp_iio.c
>>> @@ -8,6 +8,8 @@
>>>  #include <linux/iio/kfifo_buf.h>
>>>  #include <linux/module.h>
>>>  #include <linux/slab.h>
>>> +#include <linux/unaligned.h>
>>> +#include <linux/units.h>
>>>  #include "ssp_iio_sensor.h"
>>>  
>>>  /**
>>> @@ -70,7 +72,6 @@ EXPORT_SYMBOL_NS(ssp_common_buffer_postdisable, "IIO_SSP_SENSORS");
>>>  int ssp_common_process_data(struct iio_dev *indio_dev, void *buf,
>>>  			    unsigned int len, int64_t timestamp)
>>>  {
>>> -	__le32 time;
>>>  	int64_t calculated_time = 0;
>>>  	struct ssp_sensor_data *spd = iio_priv(indio_dev);
>>>  
>>> @@ -82,11 +83,7 @@ int ssp_common_process_data(struct iio_dev *indio_dev, void *buf,
>>>  	 */
>>>  	memcpy(spd->buffer, buf, len);
>>>  
>>> -	if (indio_dev->scan_timestamp) {
>>> -		memcpy(&time, &((char *)buf)[len], SSP_TIME_SIZE);
>>> -		calculated_time =
>>> -			timestamp + (int64_t)le32_to_cpu(time) * 1000000;
>>> -	}
>>> +	calculated_time = timestamp + get_unaligned_le32(buf + len) * MEGA;
>>
>> Don't we still need to cast to 64 bit to avoid multiplication overflow?
>>
> 
> Hi David,
> 
> Thanks for your message!
> 
> Aren't we already covered by the fact that MEGA is defined as an
> unsigned long?

That is only 64-bits on 64-bit architectures, so could still overflow on
32-bit architectures where long is 32-bit.

> 
> 	include/linux/units.h:12:#define MEGA 1000000UL
> 
> Cheers,
> Vasilis
> 
>>>  
>>>  	return iio_push_to_buffers_with_timestamp(indio_dev, spd->buffer,
>>>  						  calculated_time);
>>