Re: [PATCH 6/7] tty/powerpc: introduce the ePAPR embedded hypervisorbyte channel driver

From: Timur Tabi
Date: Thu May 19 2011 - 11:16:03 EST

Alan Cox wrote:
> ttys = tty_port_tty_get(&bc->port);
> stuff
> if (ttys != NULL)
> tty stuff
> tty_kref_put(ttys);

Under what circumstances can ttys be NULL? I currently only use this code in
the RX and TX interrupt handlers, which are both enabled in the
tty_port_operations.activate() function.

Is this right for the TX handler:

static irqreturn_t ehv_bc_tty_tx_isr(int irq, void *data)
struct ehv_bc_data *bc = data;
struct tty_struct *ttys = tty_port_tty_get(&bc->port);

if (ttys) {


I just want to make sure that testing for NULL is really necessary in my
interrupt handlers.

>> > + len = min_t(unsigned int,
>> > + CIRC_CNT_TO_END(bc->head, bc->tail, BUF_SIZE),
> The kfifo API is probably faster and cleaner. Much of tty still uses
> CIRC_* because they predate the new APIs.

Ok, I'll change it.

> You really also need a hangup method so vhangup() does the right thing
> and you can securely do logins etc and sessions on your console. As
> you've got no hardware entangled in this and you already use tty_port
> helpers the hangup helper will do the work for you.


> I guess the only other thing to consider is whether you want to implement
> a SYSRQ interface on your console ?

I don't think byte channels can support SYSRQ, but I'll look into it.

Timur Tabi
Linux kernel developer at Freescale

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at