Re: [PATCH] staging: pi433: enforce tx_cfg to be set before any message can be sent

[Sidong Yang <realwakka@gmail.com>]

On Sun, Jan 09, 2022 at 11:26:52AM +1300, Paulo Miguel Almeida wrote:

Hi, Paulo.
Thanks for the patch.
I have some opinion below.

> this driver relies on exposing a char device to userspace to tx
> messages. Every message can be sent using different trasmitter settings
> such so the tx_cfg must be written before sending any messages.
> Failing to do so will cause the message to fail silently depending on
> printk/dynamic_debug settings which makes it hard to troubleshoot.
> 
> This patch add a control variable that will get initialized once tx_cfg
> is set for the fd used when interacting with the char device.

I don't know that adding flag is good idea. It seems that initializing
to default is better than this.

> 
> Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
> ---
> Patch dependency: 
> - This patch needs the patch below to be applied first as both tweak the
>   same file.
> https://lore.kernel.org/lkml/20220108212728.GA7784@mail.google.com/
> 
> meta-comments:
> - I'm not entirely sure if -EPERM is the best error code to return here,
>   I'm taking suggestions
> ---
>  drivers/staging/pi433/pi433_if.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
> index 051c9052aeeb..3e9913f4bc7d 100644
> --- a/drivers/staging/pi433/pi433_if.c
> +++ b/drivers/staging/pi433/pi433_if.c
> @@ -108,6 +108,9 @@ struct pi433_device {
>  struct pi433_instance {
>  	struct pi433_device	*device;
>  	struct pi433_tx_cfg	tx_cfg;
> +
> +	/* control flags */
> +	bool			tx_cfg_initialized;
>  };
>  
>  /*-------------------------------------------------------------------------*/
> @@ -823,6 +826,16 @@ pi433_write(struct file *filp, const char __user *buf,
>  	if (count > MAX_MSG_SIZE)
>  		return -EMSGSIZE;
>  
> +	/*
> +	 * check if tx_cfg has been initialized otherwise we won't be able to
> +	 * config the RF trasmitter correctly due to invalid settings
> +	 */
> +	if (!instance->tx_cfg_initialized) {
> +		dev_dbg(device->dev,
> +			"write: failed due to uninitialized tx_cfg");
> +		return -EPERM;
> +	}
> +
>  	/*
>  	 * write the following sequence into fifo:
>  	 * - tx_cfg
> @@ -897,6 +910,7 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  			return -EFAULT;
>  		mutex_lock(&device->tx_fifo_lock);
>  		memcpy(&instance->tx_cfg, &tx_cfg, sizeof(struct pi433_tx_cfg));
> +		instance->tx_cfg_initialized = true;
>  		mutex_unlock(&device->tx_fifo_lock);
>  		break;
>  	case PI433_IOC_RD_RX_CFG:
> @@ -950,7 +964,7 @@ static int pi433_open(struct inode *inode, struct file *filp)
>  	/* setup instance data*/
>  	instance->device = device;
>  	instance->tx_cfg.bit_rate = 4711;
> -	// TODO: fill instance->tx_cfg;
> +	instance->tx_cfg_initialized = false;
>  
>  	/* instance data as context */
>  	filp->private_data = instance;
> -- 
> 2.25.4
>