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

From: Sidong Yang
Date: Sun Jan 09 2022 - 10:50:02 EST


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@xxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxx/
>
> 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
>