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

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Date:   Tue, 31 Jan 2023 11:41:53 +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 11:19:36AM +0100, Guru Mehar Rachaputi wrote:
> On Tue, Jan 31, 2023 at 06:22:23AM +0100, Greg Kroah-Hartman wrote:
> > 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?
> >
> Honestly, I followed the TODO file suggestion.

Do you have this hardware to test with?

> > > 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?
> >
> My apologies, I did not study code. While testing, the probe function of
> pi433 driver didn't appear in the lsmod operation. I suspected my
> testing was wrong.

You have to test the existing applications that talk to the device to
ensure that this works properly.  This change just breaks the
user/kernel api and doesn't actually change anything to work different
than that :(

thanks,

greg k-h