linux-kernel - Re: [PATCH RFC 3/3] ipmi: remove open coded version of SMBus block write

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Message-ID: <20210114004822.GY3348@minyard.net>
Date:   Wed, 13 Jan 2021 18:48:22 -0600
From:   Corey Minyard <minyard@....org>
To:     Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc:     linux-i2c@...r.kernel.org,
        openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org,
        Colin Ian King <colin.king@...onical.com>,
        Vijay Khemka <vijaykhemka@...com>,
        Asmaa Mnebhi <Asmaa@...lanox.com>
Subject: Re: [PATCH RFC 3/3] ipmi: remove open coded version of SMBus block
 write

On Tue, Jan 12, 2021 at 05:41:29PM +0100, Wolfram Sang wrote:
> The block-write function of the core was not used because there was no
> client-struct to use. However, in this case it seems apropriate to use a
> temporary client struct. Because we are answering a request we recieved
> when being a client ourselves. So, convert the code to use a temporary
> client and use the block-write function of the I2C core.

I asked the original authors of this about the change, and apparently is
results in a stack size warning.  Arnd Bergmann ask for it to be changed
from what you are suggesting to what it currently is.  See:

https://www.lkml.org/lkml/2019/6/19/440

So apparently this change will cause compile warnings due to the size of
struct i2c_client.

-corey

> 
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> ---
>  drivers/char/ipmi/ipmb_dev_int.c | 21 ++++++++-------------
>  1 file changed, 8 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/char/ipmi/ipmb_dev_int.c b/drivers/char/ipmi/ipmb_dev_int.c
> index 382b28f1cf2f..10d89886e5f3 100644
> --- a/drivers/char/ipmi/ipmb_dev_int.c
> +++ b/drivers/char/ipmi/ipmb_dev_int.c
> @@ -137,7 +137,7 @@ static ssize_t ipmb_write(struct file *file, const char __user *buf,
>  {
>  	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
>  	u8 rq_sa, netf_rq_lun, msg_len;
> -	union i2c_smbus_data data;
> +	struct i2c_client temp_client;
>  	u8 msg[MAX_MSG_LEN];
>  	ssize_t ret;
>  
> @@ -160,21 +160,16 @@ static ssize_t ipmb_write(struct file *file, const char __user *buf,
>  	}
>  
>  	/*
> -	 * subtract rq_sa and netf_rq_lun from the length of the msg passed to
> -	 * i2c_smbus_xfer
> +	 * subtract rq_sa and netf_rq_lun from the length of the msg. Fill the
> +	 * temporary client. Note that its use is an exception for IPMI.
>  	 */
>  	msg_len = msg[IPMB_MSG_LEN_IDX] - SMBUS_MSG_HEADER_LENGTH;
> -	if (msg_len > I2C_SMBUS_BLOCK_MAX)
> -		msg_len = I2C_SMBUS_BLOCK_MAX;
> +	memcpy(&temp_client, ipmb_dev->client, sizeof(temp_client));
> +	temp_client.addr = rq_sa;
>  
> -	data.block[0] = msg_len;
> -	memcpy(&data.block[1], msg + SMBUS_MSG_IDX_OFFSET, msg_len);
> -	ret = i2c_smbus_xfer(ipmb_dev->client->adapter, rq_sa,
> -			     ipmb_dev->client->flags,
> -			     I2C_SMBUS_WRITE, netf_rq_lun,
> -			     I2C_SMBUS_BLOCK_DATA, &data);
> -
> -	return ret ? : count;
> +	ret = i2c_smbus_write_block_data(&temp_client, netf_rq_lun, msg_len,
> +					 msg + SMBUS_MSG_IDX_OFFSET);
> +	return ret < 0 ? ret : count;
>  }
>  
>  static __poll_t ipmb_poll(struct file *file, poll_table *wait)
> -- 
> 2.29.2
>