linux-kernel - Re: [PATCH v2 2/6] mailbox: dt-bindings: Add shared [driver <=> device tree] defines

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Message-ID: <CABb+yY3jUKXXJys32bHY1u+dbdsix71Xq_H1Lrkkt27vZzmf7w@mail.gmail.com>
Date:	Mon, 10 Aug 2015 14:17:19 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernel@...inux.com, Devicetree List <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] mailbox: dt-bindings: Add shared [driver <=>
 device tree] defines

On Mon, Aug 10, 2015 at 1:54 PM, Lee Jones <lee.jones@...aro.org> wrote:
> On Mon, 10 Aug 2015, Jassi Brar wrote:
>> On Mon, Jul 27, 2015 at 3:14 PM, Lee Jones <lee.jones@...aro.org> wrote:
>> > This header is currently only used for defines pertaining to data
>> > direction i.e. Rx, Tx or Loopback.
>> >
>> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
>> > ---
>> >  include/dt-bindings/mailbox/mailbox.h | 14 ++++++++++++++
>> >  1 file changed, 14 insertions(+)
>> >  create mode 100644 include/dt-bindings/mailbox/mailbox.h
>> >
>> > diff --git a/include/dt-bindings/mailbox/mailbox.h b/include/dt-bindings/mailbox/mailbox.h
>> > new file mode 100644
>> > index 0000000..82e929a
>> > --- /dev/null
>> > +++ b/include/dt-bindings/mailbox/mailbox.h
>> > @@ -0,0 +1,14 @@
>> > +/*
>> > + * This program is free software; you can redistribute it and/or modify
>> > + * it under the terms of the GNU General Public License version 2 as
>> > + * published by the Free Software Foundation.
>> > + */
>> > +
>> > +#ifndef __MAILBOX_CONTROLLER_DT_BINDINGS_H
>> > +#define __MAILBOX_CONTROLLER_DT_BINDINGS_H
>> > +
>> > +#define MBOX_TX                0x1
>> > +#define MBOX_RX                0x2
>> > +#define MBOX_LOOPBACK  (MBOX_RX | MBOX_TX)
>> > +
>> Not sure I understand 'loopback'.  Does it mean h/w has some
>> 'loopback' mode for testing purposes? Or it simply means the
>> controller can send as well as receive messages?
>
> 'loopback' allows firmware to conduct some early function tests.
> However, channels are simplex, so we provide protection against
> multiple allocation of single channel.  By allocating a LOOPBACK
> channel we over-ride this protection and allow a single channel to be
> allocated twice, once for Rx and the other for Tx.
>
So basically hardware is half-duplex, not simplex. I think maybe you
should simply allow for RX and TX always. It should work. Just
handover any received data before send_data (reflecting the h/w
limitation). That way you don't need any such special flag.
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