linux-kernel - Re: [PATCH v3 3/3] i2c: smbus: switch from loops to memcpy

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Message-ID: <20191118074757.edyfvz5s3pqnu67y@pengutronix.de>
Date:   Mon, 18 Nov 2019 08:47:57 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Wolfram Sang <wsa@...-dreams.de>, linux-iio@...r.kernel.orgi,
        Luca Ceresoli <luca@...aceresoli.net>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] i2c: smbus: switch from loops to memcpy

Hello Dmitry,

On Tue, Nov 12, 2019 at 12:31:32PM -0800, Dmitry Torokhov wrote:
> When copying memory from one buffer to another, instead of open-coding
> loops with byte-by-byte copies let's use memcpy() which might be a bit
> faster and makes intent more clear.
> 
> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> 
> ---
> 
> Changes in v3:
> - new patch using memcpy() for moving data around
> 
>  drivers/i2c/i2c-core-smbus.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
> index 7b4e2270eeda1..bbafdd3b1b114 100644
> --- a/drivers/i2c/i2c-core-smbus.c
> +++ b/drivers/i2c/i2c-core-smbus.c
> @@ -397,8 +397,7 @@ static s32 i2c_smbus_xfer_emulated(struct i2c_adapter *adapter, u16 addr,
>  			}
>  
>  			i2c_smbus_try_get_dmabuf(&msg[0], command);
> -			for (i = 1; i < msg[0].len; i++)
> -				msg[0].buf[i] = data->block[i - 1];
> +			memcpy(msg[0].buf + 1, data->block, msg[0].len - 1);

Can it happen that msg[0].len is zero?

>  		}
>  		break;
>  	case I2C_SMBUS_BLOCK_PROC_CALL:

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |