linux-kernel - Re: [PATCH v1 10/17] iio: chemical: bme680: Remove duplicate register read

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Date: Sun, 2 Jun 2024 13:50:36 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Vasileios Amoiridis <vassilisamir@...il.com>
Cc: lars@...afoo.de, himanshujha199640@...il.com, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 10/17] iio: chemical: bme680: Remove duplicate
 register read

On Mon, 27 May 2024 20:37:58 +0200
Vasileios Amoiridis <vassilisamir@...il.com> wrote:

> The LSB of the gas register was read first to check if the following
> check was correct and then the MSB+LSB were read together. Simplify
> this by reading together the MSB+LSB immediately.
> 
> Signed-off-by: Vasileios Amoiridis <vassilisamir@...il.com>
A few trivial things. I wrote a nice comment on dma safe buffers then
noticed this does a custom regmap using spi_write_then_read() so despite
not looking like it from this code, DMA safe buffers are used.
Just thought I'd mention it for any other reviewers!

> ---
>  drivers/iio/chemical/bme680_core.c | 21 ++++++++-------------
>  1 file changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iio/chemical/bme680_core.c b/drivers/iio/chemical/bme680_core.c
> index 96423861c79a..681f271f9b06 100644
> --- a/drivers/iio/chemical/bme680_core.c
> +++ b/drivers/iio/chemical/bme680_core.c
> @@ -748,7 +748,7 @@ static int bme680_read_gas(struct bme680_data *data,
>  	int ret;
>  	__be16 tmp = 0;
>  	unsigned int check;
> -	u16 adc_gas_res;
> +	u16 adc_gas_res, gas_regs_val;
>  	u8 gas_range;
>  
>  	/* Set heater settings */
> @@ -771,11 +771,14 @@ static int bme680_read_gas(struct bme680_data *data,
>  		return -EBUSY;
>  	}
>  
> -	ret = regmap_read(data->regmap, BME680_REG_GAS_R_LSB, &check);
> +	ret = regmap_bulk_read(data->regmap, BME680_REG_GAS_MSB,
> +			       &tmp, sizeof(tmp)); 
>  	if (ret < 0) {
> -		dev_err(dev, "failed to read gas_r_lsb register\n");
> +		dev_err(dev, "failed to read gas resistance\n");
>  		return ret;
>  	}
> +	gas_regs_val = be16_to_cpu(tmp);
> +	adc_gas_res = gas_regs_val >> BME680_ADC_GAS_RES_SHIFT;
I'd rather see this as a FIELD_GET() but given this was what was originally
here I guess I can cope with keeping it a little longer!

>  
>  	/*
>  	 * occurs if either the gas heating duration was insuffient
> @@ -783,20 +786,12 @@ static int bme680_read_gas(struct bme680_data *data,
>  	 * heater temperature was too high for the heater sink to
>  	 * reach.
>  	 */
> -	if ((check & BME680_GAS_STAB_BIT) == 0) {
> +	if ((gas_regs_val & BME680_GAS_STAB_BIT) == 0) {
>  		dev_err(dev, "heater failed to reach the target temperature\n");
>  		return -EINVAL;
>  	}
>  
> -	ret = regmap_bulk_read(data->regmap, BME680_REG_GAS_MSB,
> -			       &tmp, sizeof(tmp));
> -	if (ret < 0) {
> -		dev_err(dev, "failed to read gas resistance\n");
> -		return ret;
> -	}
> -
> -	gas_range = check & BME680_GAS_RANGE_MASK;
> -	adc_gas_res = be16_to_cpu(tmp) >> BME680_ADC_GAS_RES_SHIFT;
> +	gas_range = gas_regs_val & BME680_GAS_RANGE_MASK;

Whilst you are here, may this a FIELD_GET() so we don't have to go
check that it includes the LSB.

>  
>  	*val = bme680_compensate_gas(data, adc_gas_res, gas_range);
>  	return IIO_VAL_INT;