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Date:   Wed, 12 Aug 2020 10:44:03 +0200
From:   Jens Wiklander <jens.wiklander@linaro.org>
To:     Jorge Ramirez-Ortiz <jorge@foundries.io>
Cc:     sumit.garg@linaro.org, ricardo@foundries.io, mike@foundries.io,
        tee-dev@lists.linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCHv7] drivers: optee: allow op-tee to access devices on the
 i2c bus
Message-ID: <20200812084403.GA19230@jade>
References: <20200811175531.10771-1-jorge@foundries.io>
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In-Reply-To: <20200811175531.10771-1-jorge@foundries.io>
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On Tue, Aug 11, 2020 at 07:55:31PM +0200, Jorge Ramirez-Ortiz wrote:
> Some secure elements like NXP's SE050 sit on I2C buses. For OP-TEE to
> control this type of cryptographic devices it needs coordinated access
> to the bus, so collisions and RUNTIME_PM dont get in the way.
> 
> This trampoline driver allow OP-TEE to access them.
> 
> Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
> ---
>  v7: add support for ten bit i2c slave addressing
>  v6: compile out if CONFIG_I2C not enabled
>  v5: alphabetic order of includes
>  v4: remove unnecessary extra line in optee_msg.h
>  v3: use from/to msg param to support all types of memory
>      modify OPTEE_MSG_RPC_CMD_I2C_TRANSFER message id
>      
>  drivers/tee/optee/optee_msg.h | 21 ++++++++
>  drivers/tee/optee/rpc.c       | 95 +++++++++++++++++++++++++++++++++++
>  2 files changed, 116 insertions(+)
> 
> diff --git a/drivers/tee/optee/optee_msg.h b/drivers/tee/optee/optee_msg.h
> index 795bc19ae17a..7b2d919da2ac 100644
> --- a/drivers/tee/optee/optee_msg.h
> +++ b/drivers/tee/optee/optee_msg.h
> @@ -419,4 +419,25 @@ struct optee_msg_arg {
>   */
>  #define OPTEE_MSG_RPC_CMD_SHM_FREE	7
>  
> +/*
> + * Access a device on an i2c bus
> + *
> + * [in]  param[0].u.value.a		mode: RD(0), WR(1)
> + * [in]  param[0].u.value.b		i2c adapter
> + * [in]  param[0].u.value.c		i2c chip
> + *
> + * [in]  param[1].u.value.a		i2c control flags
> + *
> + * [in/out] memref[2]			buffer to exchange the transfer data
> + *					with the secure world
> + *
> + * [out]  param[3].u.value.a		bytes transferred by the driver
> + */
> +#define OPTEE_MSG_RPC_CMD_I2C_TRANSFER 21
> +/* I2C master transfer modes */
> +#define OPTEE_MSG_RPC_CMD_I2C_TRANSFER_RD 0
> +#define OPTEE_MSG_RPC_CMD_I2C_TRANSFER_WR 1
> +/* I2C master control flags */
> +#define OPTEE_MSG_RPC_CMD_I2C_FLAGS_TEN_BIT  BIT(0)
> +
>  #endif /* _OPTEE_MSG_H */
> diff --git a/drivers/tee/optee/rpc.c b/drivers/tee/optee/rpc.c
> index b4ade54d1f28..b6178761d79f 100644
> --- a/drivers/tee/optee/rpc.c
> +++ b/drivers/tee/optee/rpc.c
> @@ -7,6 +7,7 @@
>  
>  #include <linux/delay.h>
>  #include <linux/device.h>
> +#include <linux/i2c.h>
>  #include <linux/slab.h>
>  #include <linux/tee_drv.h>
>  #include "optee_private.h"
> @@ -49,6 +50,97 @@ static void handle_rpc_func_cmd_get_time(struct optee_msg_arg *arg)
>  	arg->ret = TEEC_ERROR_BAD_PARAMETERS;
>  }
>  
> +#if IS_ENABLED(CONFIG_I2C)
> +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;
> +	int i, ret = -EOPNOTSUPP;
> +	uint32_t attr[] = {
uint32_t seems a randomly chosen type here. The
TEE_IOCTL_PARAM_ATTR_TYPE_* defines fit in a u8.
Consider u8 attr[] = { instead.

> +		TEE_IOCTL_PARAM_ATTR_TYPE_VALUE_INPUT,
> +		TEE_IOCTL_PARAM_ATTR_TYPE_VALUE_INPUT,
> +		TEE_IOCTL_PARAM_ATTR_TYPE_MEMREF_INOUT,
> +		TEE_IOCTL_PARAM_ATTR_TYPE_VALUE_OUTPUT,
> +	};
> +
> +	if (arg->num_params != ARRAY_SIZE(attr)) {
> +		arg->ret = TEEC_ERROR_BAD_PARAMETERS;
> +		return;
> +	}
> +
> +	params = kmalloc_array(arg->num_params, sizeof(struct tee_param),
> +			       GFP_KERNEL);
> +	if (!params) {
> +		arg->ret = TEEC_ERROR_OUT_OF_MEMORY;
> +		return;
> +	}
> +
> +	if (optee_from_msg_param(params, arg->num_params, arg->params))
> +		goto bad;
> +
> +	for (i = 0; i < arg->num_params; i++) {
arg->num_params has an unsigned type. Consider giving i an unsigned type
too.

> +		if ((params[i].attr & TEE_IOCTL_PARAM_ATTR_TYPE_MASK)
> +		    != attr[i])
It looks a bit funny with the comparison at the beginning of the line,
normally we try to leave those at the end of the line. But
optee_from_msg_param() doesn't set any higher bits in params[i].attr so
you could also simplify the expression as:
		if (params[i].attr != attr[i])

> +			goto bad;
> +	}
> +
> +	client.adapter = i2c_get_adapter(params[0].u.value.b);
> +	if (!client.adapter)
> +		goto bad;
> +
> +	if (params[1].u.value.a & OPTEE_MSG_RPC_CMD_I2C_FLAGS_TEN_BIT) {
> +		if (!i2c_check_functionality(client.adapter,
> +					     I2C_FUNC_10BIT_ADDR)) {
> +			i2c_put_adapter(client.adapter);
> +			goto bad;
> +		}
> +
> +		client.flags = I2C_CLIENT_TEN;
> +	}
> +
> +	client.addr = params[0].u.value.c;
> +	snprintf(client.name, I2C_NAME_SIZE, "i2c%d", client.adapter->nr);
> +
> +	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);
> +		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);
> +		goto bad;
> +	}
> +
> +	if (ret < 0) {
> +		arg->ret = TEEC_ERROR_COMMUNICATION;
> +	} else {
> +		params[3].u.value.a = ret;
> +		arg->ret = TEEC_SUCCESS;
> +
> +		if (optee_to_msg_param(arg->params, arg->num_params, params))
> +			arg->ret = TEEC_ERROR_BAD_PARAMETERS;
Need
arg->ret = TEEC_SUCCESS;
when everything is OK.

> +	}
> +
> +	i2c_put_adapter(client.adapter);
> +	kfree(params);
> +	return;
> +bad:
> +	kfree(params);
> +	arg->ret = TEEC_ERROR_BAD_PARAMETERS;
> +}
> +#else
> +static void handle_rpc_func_cmd_i2c_transfer(struct tee_context *ctx,
> +					     struct optee_msg_arg *arg)
> +{
> +	arg->ret = TEEC_ERROR_COMMUNICATION;
I'd prefer TEEC_ERROR_NOT_SUPPORTED here.
TEEC_ERROR_NOT_SUPPORTED would need to be defined as:
#define TEEC_ERROR_NOT_SUPPORTED        0xFFFF000A
in optee_private.h

Cheers,
Jens

> +}
> +#endif
> +
>  static struct wq_entry *wq_entry_get(struct optee_wait_queue *wq, u32 key)
>  {
>  	struct wq_entry *w;
> @@ -382,6 +474,9 @@ static void handle_rpc_func_cmd(struct tee_context *ctx, struct optee *optee,
>  	case OPTEE_MSG_RPC_CMD_SHM_FREE:
>  		handle_rpc_func_cmd_shm_free(ctx, arg);
>  		break;
> +	case OPTEE_MSG_RPC_CMD_I2C_TRANSFER:
> +		handle_rpc_func_cmd_i2c_transfer(ctx, arg);
> +		break;
>  	default:
>  		handle_rpc_supp_cmd(ctx, arg);
>  	}
> -- 
> 2.17.1
>