Hi Sean.
> > > ret *= sizeof(unsigned int);
> > >
> > > - /*
> > > - * The lircd gap calculation expects the write function to
> > > - * wait for the actual IR signal to be transmitted before
> > > - * returning.
> > > - */
> > > - towait = ktime_us_delta(ktime_add_us(start, duration), ktime_get());
> > > - if (towait > 0) {
> > > - set_current_state(TASK_INTERRUPTIBLE);
> > > - schedule_timeout(usecs_to_jiffies(towait));
> > > + if (!lirc->tx_no_wait) {
> > > + /*
> > > + * The lircd gap calculation expects the write function to
> > > + * wait for the actual IR signal to be transmitted before
> > > + * returning.
> > > + */
> > > + towait = ktime_us_delta(ktime_add_us(start, duration),
> > > + ktime_get());
> > > + if (towait > 0) {
> > > + set_current_state(TASK_INTERRUPTIBLE);
> > > + schedule_timeout(usecs_to_jiffies(towait));
> > > + }
> > > }
> > > -
> >
> > this doesn't fix my problem, though.
> >
> > This approach gives the userspace the possibility to choose to
> > either sync or not. In my case the sync happens, but in a
> > different level and it's not up to the userspace to make the
> > decision.
>
> What problem are you trying to solve?
>
> I wrote this patch as a response to this patch:
>
> https://lkml.org/lkml/2016/9/1/653
Actually no big problem here but what I wrote below.
If the user sets LIRC_SET_TRANSMITTER_WAIT to 0 and the driver
waits anyway, this patch wouldn't be of any use and it would
do exactly what it whas doing before.
> In the spi case, the driver already waits for the IR to complete so the
> wait in ir_lirc_transmit_ir() is unnecessary. However it does not end up
> waiting. There are other drivers like yours that wait for the IR to
> complete (ene_ir, ite-cir). Since towait in ir_lirc_transmit_ir is the
> delta between before and after the driver transmits, it will be 0 and
> will never goto into schedule_timeout(), barring some very minor rounding
> differences.
>
> > Besides, I see here a security issue: what happens if userspace
> > does something like
> >
> > fd = open("/dev/lirc0", O_RDWR);
> >
> > ioctl(fd, LIRC_SET_TRANSMITTER_WAIT, 0);
> >
> > while(1)
> > write(fd, buffer, ENORMOUS_BUFFER_SIZE);
>
> I don't understand what problem this would introduce.
>
> You can't write more than 512 pulse/spaces and each write cannot
> have more than 500ms in IR (so adding up the pulses and spaces). The driver
> should only send once the previous send completed.
OK.
> > > + case LIRC_SET_TRANSMITTER_WAIT:
> > > + if (!dev->tx_ir)
> > > + return -ENOTTY;
> > > +
> > > + lirc->tx_no_wait = !val;
> > > + break;
> > > +
> >
> > Here I see an innocuous bug. Depending on the hardware (for
> > example ir-spi) it might happen that the device waits in any
> > case (in ir-spi the sync is done by the spi). This means that if
> > userspace sets 'tx_no_wait = true', the device/driver doesn't
> > care and waits anyway, doing the opposite from what is described
> > in the ABI.
> >
> > Here we could call a dev->tx_set_transmitter_wait(...) function
> > that sets the value or returns error in case the wait is not
> > feasable, something like:
> >
> > case LIRC_SET_TRANSMITTER_WAIT:
> > if (!dev->tx_ir)
> > return -ENOTTY;
> >
> > if (dev->tx_set_transmitter_wait)
> > return dev->tx_set_transmitter_wait(lirc, val);
> >
> > lirc->tx_no_wait = !val;
> > break;
>
> That is true. Do you want the ir-spi driver to be able to send without
> waiting?
I think there should be some meccanism to keep it coherent with
the ABI, mine was a suggestion.
> > > --- a/drivers/media/rc/rc-core-priv.h
> > > +++ b/drivers/media/rc/rc-core-priv.h
> > > @@ -112,7 +112,7 @@ struct ir_raw_event_ctrl {
> > > u64 gap_duration;
> > > bool gap;
> > > bool send_timeout_reports;
> > > -
> > > + bool tx_no_wait;
> > > } lirc;
> >
> > this to me looks confusing, it has a negative meaning in kernel
> > space and a positive meaning in userspace. Can't we call it
> > lirc->tx_wait instead of lirc->tx_no_wait, so that we keep the
> > same meaning and we don't need to negate val?
>
> This was just done to avoid having to initialise to true (non-zero).
OK, this was just a nitpick anyway :)
Thanks,
Andi
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