linux-kernel - RE: [RFC 1/8] serial:st-asc: Add ST ASC driver.

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Date:	Thu, 23 May 2013 18:26:09 +0200
From:	Stephen GALLIMORE <stephen.gallimore@...com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: RE: [RFC 1/8] serial:st-asc: Add ST ASC driver.


On Wednesday 22 May 2013, Arnd Bergmann wrote:
> > Also all of the custom_divisor functionality is basically commented as "old"
> > or has a kernel warning saying it is deprecated (see uart_set_info), so as
> > far as I can see for our (and I suspect most) hardware it is completely
> > irrelevant functionality.
> 
> What may have happened here is that custom_divisor was used in a different
> way when I added that code than it is today, and the change was not propagated
> into the of_serial driver. However, going back to 2.6.20 shows no different
> code than what we have today in this regard. It may simply have been
> a mistake on my side.

Thanks for looking into this and digging around in the history. At least I didn't
miss something really obvious.

> I looked it up in the original serial port binding at
> http://www.openfirmware.org/1275/bindings/devices/html/serial.ht
> ml, which does
> not specify the property, and in ePAPR, which does have it in the
> section about
> "serial class devices":
> 
> 18 6.2.1.2 current-speed
> 19 Property: current-speed
> 20 Value type: <u32>
> 21 Description:
> 22 Specifies the current speed of a serial device in bits per second. A
> boot program should set
> 23 this property if it has initialized the serial device.
> 24 Example:
> 25 current - speed = <115200>; # 115200 baud
> 
> The reason you want this is so that the driver can initialize the hardware from
> scratch more easily and get back to the same settings. Why they only specified
> the baud rate but not also start/stop bits and flow control I don't understand
> though.

Yes, I had been made aware of the ePAPR definition by Srini after I sent the post.
In fact I had exactly the same question in my head about the other settings as
well.  

> 
> I guess you can ignore my original comment.
> 
OK.

Thanks again for your time.

Regards,
-stephen
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