linux-kernel - RE: [PATCH v1] serial: uart: add hw flow control support configuration

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Date:	Thu, 1 May 2014 18:57:18 +0000
From:	"Karicheri, Muralidharan" <m-karicheri2@...com>
To:	Mark Rutland <mark.rutland@....com>
CC:	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"Kumar Gala" <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	"Shilimkar, Santosh" <santosh.shilimkar@...com>
Subject: RE: [PATCH v1] serial: uart: add hw flow control support
 configuration

>-----Original Message-----
>From: Mark Rutland [mailto:mark.rutland@....com]
>Sent: Tuesday, April 29, 2014 6:28 PM
>To: Karicheri, Muralidharan
>Cc: linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org; linux-serial@...r.kernel.org;
>devicetree@...r.kernel.org; Rob Herring; Ian Campbell; Kumar Gala; Randy Dunlap; Greg
>Kroah-Hartman; Jiri Slaby; Shilimkar, Santosh
>Subject: Re: [PATCH v1] serial: uart: add hw flow control support configuration
>
>Hi,
>
>On Tue, Apr 29, 2014 at 06:22:02PM +0100, Murali Karicheri wrote:
>> 8250 uart driver currently supports only software assisted hw flow
>> control. The software assisted hw flow control maintains a hw_stopped
>> flag in the tty structure to stop and start transmission and use modem
>> status interrupt for the event to drive the handshake signals. This is
>> not needed if hw has flow control capabilities. This patch adds a DT
>> attribute for enabling hw flow control for a uart port. Also skip stop
>> and start if this flag is present in flag field of the port structure.
>>
>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>>
>> CC: Rob Herring <robh+dt@...nel.org>
>> CC: Pawel Moll <pawel.moll@....com>
>> CC: Mark Rutland <mark.rutland@....com>
>> CC: Ian Campbell <ijc+devicetree@...lion.org.uk>
>> CC: Kumar Gala <galak@...eaurora.org>
>> CC: Randy Dunlap <rdunlap@...radead.org>
>> CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> CC: Jiri Slaby <jslaby@...e.cz>
>> CC: Santosh Shilimkar <santosh.shilimkar@...com>
>> ---
>>  - Fixed brackets around port->flags & UPF_HARD_FLOW as per comments
>>  .../devicetree/bindings/serial/of-serial.txt       |    2 ++
>>  drivers/tty/serial/8250/8250_core.c                |    6 ++++--
>>  drivers/tty/serial/of_serial.c                     |    4 ++++
>>  drivers/tty/serial/serial_core.c                   |   12 +++++++++---
>>  4 files changed, 19 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/serial/of-serial.txt
>> b/Documentation/devicetree/bindings/serial/of-serial.txt
>> index 1928a3e..123de01 100644
>> --- a/Documentation/devicetree/bindings/serial/of-serial.txt
>> +++ b/Documentation/devicetree/bindings/serial/of-serial.txt
>> @@ -37,6 +37,8 @@ Optional properties:
>>  - auto-flow-control: one way to enable automatic flow control support. The
>>    driver is allowed to detect support for the capability even without this
>>    property.
>> +- hw-flow-control: this enables pure hw flow control and no software
>> +  intervention needed.
>
>>From the wording of the commit message, I believe this would be better worded
>something like:
>
>- hw-flow-control: the hardware has flow control capability.
>
>While the OS needs to know that flow control is present if it wishes to make use of it,
>whether or not the OS does so is not a matter for the binding.
>
>It might also be better worded as "has-hw-flow-control", which would make that
>distinction clearer.
>
>Otherwise this looks fine to me.

Fine. Will re-send with rewording as

has-hw-flow-control: the hardware has flow control capability.

Murali
>
>Thanks,
>Mark.
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