linux-kernel - Re: [PATCH v2 5/7] [media] ir-lirc-codec: don't wait any transmitting time for tx only devices

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Message-id: <20161027074401.wxg5icc6hcpwnfsf@gangnam.samsung>
Date:   Thu, 27 Oct 2016 16:44:01 +0900
From:   Andi Shyti <andi.shyti@...sung.com>
To:     Sean Young <sean@...s.org>
Cc:     Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andi Shyti <andi@...zian.org>,
        David Härdeman <david@...deman.nu>
Subject: Re: [PATCH v2 5/7] [media] ir-lirc-codec: don't wait any transmitting
 time for tx only devices

Hi Sean,

it's been a while :)

I was going through your review fixing what needs to be fixed,
but...

> > @@ -153,7 +153,7 @@ static ssize_t ir_lirc_transmit_ir(struct file *file, const char __user *buf,
> >  	}
> >  
> >  	ret = dev->tx_ir(dev, txbuf, count);
> > -	if (ret < 0)
> > +	if (ret < 0 || dev->driver_type == RC_DRIVER_IR_RAW_TX)
> 
> Just because a driver only does transmit doesn't mean its transmit ABI
> should change.
> 
> Now this bit of code is pretty horrible. It ensures that the call to write()
> takes at least as long as the length of the transmit IR by sleeping. That's
> not much of a guarantee that the IR has been sent.
> 
> Note that in the case of ir-spi, since your spi transfer is sync no sleep
> should be introduced here.
> 
> The gap calculation in lirc checks that if the call to write() took _longer_
> than expected wait before sending the next IR code (when either multiple
> IR codes or repeats are specified). Introducing the sleep in the kernel
> here does not help at all, lirc already ensures that it waits as long as
> the IR is long (see schedule_repeat_timer in lirc).
> 
> This change was introduced in 3.10, commit f8e00d5. 

... I'm not sure what can be done here. I get your point and I
understand that this indeed is a kind of fake sync point and by
doing this I 

How about creating two different functions:

- ir_lirc_transmit_ir where we actually do what the function
  already does
- ir_lirc_transmit_no_sync where the function we don't wait
  because the the sync is done on a different level (for example
  in the SPI case).

SPI does approximately the same thing.

Andi