linux-kernel - Re: [PATCH] optee: simplify i2c access

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Date:   Tue, 26 Jan 2021 09:08:27 +0100
From:   "Jorge Ramirez-Ortiz, Foundries" <jorge@...ndries.io>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Jens Wiklander <jens.wiklander@...aro.org>,
        Jorge Ramirez-Ortiz <jorge@...ndries.io>,
        Arnd Bergmann <arnd@...db.de>,
        op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] optee: simplify i2c access

On 25/01/21, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> Storing a bogus i2c_client structure on the stack adds overhead and
> causes a compile-time warning:
> 
> drivers/tee/optee/rpc.c:493:6: error: stack frame size of 1056 bytes in function 'optee_handle_rpc' [-Werror,-Wframe-larger-than=]
> void optee_handle_rpc(struct tee_context *ctx, struct optee_rpc_param *param,
> 
> Change the implementation of handle_rpc_func_cmd_i2c_transfer() to
> open-code the i2c_transfer() call, which makes it easier to read
> and avoids the warning.
> 
> Fixes: c05210ab9757 ("drivers: optee: allow op-tee to access devices on the i2c bus")

does fixing stack-frame compile warnings need a 'fixes' tag?

> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/tee/optee/rpc.c | 31 ++++++++++++++++---------------
>  1 file changed, 16 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/tee/optee/rpc.c b/drivers/tee/optee/rpc.c
> index 1e3614e4798f..6cbb3643c6c4 100644
> --- a/drivers/tee/optee/rpc.c
> +++ b/drivers/tee/optee/rpc.c
> @@ -54,8 +54,9 @@ static void handle_rpc_func_cmd_get_time(struct optee_msg_arg *arg)
>  static void handle_rpc_func_cmd_i2c_transfer(struct tee_context *ctx,
>  					     struct optee_msg_arg *arg)
>  {
> -	struct i2c_client client = { 0 };
>  	struct tee_param *params;
> +	struct i2c_adapter *adapter;
> +	struct i2c_msg msg = { };
>  	size_t i;
>  	int ret = -EOPNOTSUPP;
>  	u8 attr[] = {
> @@ -85,48 +86,48 @@ static void handle_rpc_func_cmd_i2c_transfer(struct tee_context *ctx,
>  			goto bad;
>  	}
>  
> -	client.adapter = i2c_get_adapter(params[0].u.value.b);
> -	if (!client.adapter)
> +	adapter = i2c_get_adapter(params[0].u.value.b);
> +	if (!adapter)
>  		goto bad;
>  
>  	if (params[1].u.value.a & OPTEE_MSG_RPC_CMD_I2C_FLAGS_TEN_BIT) {
> -		if (!i2c_check_functionality(client.adapter,
> +		if (!i2c_check_functionality(adapter,
>  					     I2C_FUNC_10BIT_ADDR)) {
> -			i2c_put_adapter(client.adapter);
> +			i2c_put_adapter(adapter);
>  			goto bad;
>  		}
>  
> -		client.flags = I2C_CLIENT_TEN;
> +		msg.flags = I2C_M_TEN;
>  	}
>  
> -	client.addr = params[0].u.value.c;
> -	snprintf(client.name, I2C_NAME_SIZE, "i2c%d", client.adapter->nr);
> +	msg.addr = params[0].u.value.c;
> +	msg.buf  = params[2].u.memref.shm->kaddr;
> +	msg.len  = params[2].u.memref.size;
>  
>  	switch (params[0].u.value.a) {
>  	case OPTEE_MSG_RPC_CMD_I2C_TRANSFER_RD:
> -		ret = i2c_master_recv(&client, params[2].u.memref.shm->kaddr,
> -				      params[2].u.memref.size);
> +		msg.flags |= I2C_M_RD;
>  		break;
>  	case OPTEE_MSG_RPC_CMD_I2C_TRANSFER_WR:
> -		ret = i2c_master_send(&client, params[2].u.memref.shm->kaddr,
> -				      params[2].u.memref.size);
>  		break;
>  	default:
> -		i2c_put_adapter(client.adapter);
> +		i2c_put_adapter(adapter);
>  		goto bad;
>  	}
>  
> +	ret = i2c_transfer(adapter, &msg, 1);
> +
>  	if (ret < 0) {
>  		arg->ret = TEEC_ERROR_COMMUNICATION;
>  	} else {
> -		params[3].u.value.a = ret;
> +		params[3].u.value.a = msg.len;
>  		if (optee_to_msg_param(arg->params, arg->num_params, params))
>  			arg->ret = TEEC_ERROR_BAD_PARAMETERS;
>  		else
>  			arg->ret = TEEC_SUCCESS;
>  	}
>  
> -	i2c_put_adapter(client.adapter);
> +	i2c_put_adapter(adapter);
>  	kfree(params);
>  	return;
>  bad:
> -- 
> 2.29.2
>