linux-kernel - Re: [PATCH 2/2] tty: serial: msm: Support sysrq on uartDM devices

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Date:	Thu, 30 Oct 2014 23:41:30 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
	Frank Rowand <frank.rowand@...ymobile.com>
Subject: Re: [PATCH 2/2] tty: serial: msm: Support sysrq on uartDM devices

On 10/30, Daniel Thompson wrote:
> On 29/10/14 18:14, Stephen Boyd wrote:
> > +		r_count = min_t(int, count, sizeof(buf));
> > +
> > +		for (i = 0; i < r_count; i++) {
> > +			char flag = TTY_NORMAL;
> >  
> > -		/* TODO: handle sysrq */
> > -		tty_insert_flip_string(tport, buf, min(count, 4));
> > -		count -= 4;
> > +			if (msm_port->break_detected && buf[i] == 0) {
> > +				port->icount.brk++;
> > +				flag = TTY_BREAK;
> > +				msm_port->break_detected = false;
> > +				if (uart_handle_break(port))
> > +					continue;
> > +			}
> > +
> > +			if (!(port->read_status_mask & UART_SR_RX_BREAK))
> > +				flag = TTY_NORMAL;
> 
> flag is already known to be TTY_NORMAL.

Huh? If we detected a break we would set the flag to TTY_BREAK
and if uart_handle_break() returned 0 (perhaps sysrq config is
diasbled) then we would get down here, and then we want to reset
the flag to TTY_NORMAL if the read_status_mask bits indicate that
we want to skip checking for breaks. Otherwise we want to
indicate to the tty layer that it's a break character.

> 
> 
> > +
> > +			spin_unlock(&port->lock);
> 
> Is it safe to unlock at this point? count may no longer be valid when we
> return.

Can you explain further? If it actually isn't valid something
needs to be done. I believe other serial drivers are doing this
sort of thing though so it doesn't seem that uncommon (of course
those drivers could also be broken I suppose).

> 
> 
> > +			sysrq = uart_handle_sysrq_char(port, buf[i]);
> > +			spin_lock(&port->lock);
> > +			if (!sysrq)
> > +				tty_insert_flip_char(tport, buf[i], flag);
> 
> flag has a constant value here.
> 

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