[V2,04/13] USB: serial: digi_acceleport: Remove in_interrupt() usage

From: Ahmed S. Darwish <a.darwish@linutronix.de>

The usage of in_interrupt() in drivers is phased out and Linus clearly
requested that code which changes behaviour depending on context should
either be separated or the context be conveyed in an argument passed by the
caller, which usually knows the context.

The debug printk() in digi_write() prints in_interrupt() as context
information. TTY writes happen always in preemptible task context and
console writes can happen from almost any context, so in_interrupt() is not
really helpful.

Aside of that issuing a printk() from a console->write() callback is not a
really brilliant idea for obvious reasons.

Remove the in_interrupt() printout and make the printk() depend on tty.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Johan Hovold <johan@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org

---
 drivers/usb/serial/digi_acceleport.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

On Mon, Oct 19, 2020 at 12:06:33PM +0200, Thomas Gleixner wrote:
> From: Ahmed S. Darwish <a.darwish@linutronix.de>
> 
> The usage of in_interrupt() in drivers is phased out and Linus clearly
> requested that code which changes behaviour depending on context should
> either be separated or the context be conveyed in an argument passed by the
> caller, which usually knows the context.
> 
> The debug printk() in digi_write() prints in_interrupt() as context
> information. TTY writes happen always in preemptible task context and
> console writes can happen from almost any context, so in_interrupt() is not
> really helpful.

The above statement is not correct, TTY writes can and do happen from
other contexts, including soft IRQ (e.g. PPP).

> Aside of that issuing a printk() from a console->write() callback is not a
> really brilliant idea for obvious reasons.

True, but we don't need to sprinkle conditionals for the benefit of
people trying to debug USB serial drivers using a USB serial console.
They get what they deserve. ;)

> Remove the in_interrupt() printout and make the printk() depend on tty.
> 
> Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Johan Hovold <johan@kernel.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: linux-usb@vger.kernel.org
> 
> ---
>  drivers/usb/serial/digi_acceleport.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> --- a/drivers/usb/serial/digi_acceleport.c
> +++ b/drivers/usb/serial/digi_acceleport.c
> @@ -911,9 +911,10 @@ static int digi_write(struct tty_struct
>  	unsigned char *data = port->write_urb->transfer_buffer;
>  	unsigned long flags = 0;
>  
> -	dev_dbg(&port->dev,
> -		"digi_write: TOP: port=%d, count=%d, in_interrupt=%ld\n",
> -		priv->dp_port_num, count, in_interrupt());
> +	if (tty) {
> +		dev_dbg(&port->dev, "digi_write: TOP: port=%d, count=%d\n",
> +			priv->dp_port_num, count);
> +	}

So just drop the in_interrupt() here.

Also note that we already have another unconditional dev_dbg() at the
end of this function.

>  
>  	/* copy user data (which can sleep) before getting spin lock */
>  	count = min(count, port->bulk_out_size-2);
> 

Johan

On Mon, Oct 26, 2020 at 03:03:13PM +0100, Sebastian Andrzej Siewior wrote:
> From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
> 
> The usage of in_interrupt() in drivers is phased out and Linus clearly
> requested that code which changes behaviour depending on context should
> either be separated or the context be conveyed in an argument passed by the
> caller, which usually knows the context.
> 
> The debug printk() in digi_write() prints in_interrupt() as context
> information. This information is imprecisely as it does not distinguish
> between hard-IRQ or disabled botton half and it does consider disabled
> interrupts or preemption. It is not really helpful.

I fixed up a couple of typos and added the missing negation above so
that it reads:

  The debug printk() in digi_write() prints in_interrupt() as context
  information. This information is imprecise as it does not distinguish
  between hard-IRQ or disabled bottom half and it does not consider
  disabled interrupts or preemption. It is not really helpful.
	
> Remove the in_interrupt() printout.
> 
> Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Cc: Johan Hovold <johan@kernel.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: linux-usb@vger.kernel.org
> ---
> v2…v3:
>   - Don't make dev_dbg() conditional on `tty'
>   - Remove the part "tty happens always in process context" from the
>     commit message. Johan pointed out that for PPP it may happen in
>     bottom half.

Now applied for -next, thanks.

Johan