linux-kernel - Re: [PATCH] staging: pi433: modify bit

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Message-ID: <Y9ilj812USHrSXe+@kroah.com>
Date:   Tue, 31 Jan 2023 06:22:23 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Guru Mehar Rachaputi <gurumeharrachaputi@...il.com>
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: pi433: modify bit_rate from u16 to u32

On Tue, Jan 31, 2023 at 03:11:38AM +0100, Guru Mehar Rachaputi wrote:
> (struct pi433_tx_cfg)->bit_rate is modified from u16 to u32 to
> support bit rates up to 300kbps per the spec

What spec?

And how can changing the size of a variable that crosses the user/kernel
boundry like this change the bit rate max?

> 
> Signed-off-by: Guru Mehar Rachaputi <gurumeharrachaputi@...il.com>
> ---
>  drivers/staging/pi433/pi433_if.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/pi433/pi433_if.h b/drivers/staging/pi433/pi433_if.h
> index 25ee0b77a32c..1f8ffaf02d99 100644
> --- a/drivers/staging/pi433/pi433_if.h
> +++ b/drivers/staging/pi433/pi433_if.h
> @@ -51,7 +51,7 @@ enum option_on_off {
>  #define PI433_TX_CFG_IOCTL_NR	0
>  struct pi433_tx_cfg {
>  	__u32			frequency;
> -	__u16			bit_rate;
> +	__u32			bit_rate;
>  	__u32			dev_frequency;
>  	enum modulation		modulation;
>  	enum mod_shaping	mod_shaping;

And didn't you just break existing userspace code?  If not, how?  If so,
how did you test this?

thanks,

greg k-h