linux-kernel - Re: inverse mapping from a struct console to device

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Date:	Wed, 28 Jan 2015 17:48:29 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Jon Masters <jcm@...hat.com>, Mark Rutland <mark.rutland@....com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"leif.lindholm@...aro.org" <leif.lindholm@...aro.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Andre Przywara <Andre.Przywara@....com>,
	Torez Smith <torez@...hat.com>
Subject: Re: inverse mapping from a struct console to device

Hi Jon,

On 01/27/2015 03:42 PM, Jon Masters wrote:
> On 01/27/2015 07:30 AM, Mark Rutland wrote:
>> On Tue, Jan 27, 2015 at 11:54:18AM +0000, Jon Masters wrote:
> 
>>> Here's an example of the data we get in the SPCR for reference:
>>>
>>> [0012]               Serial Port Register : [Generic Address Structure]
>>> [0001]                           Space ID : 00 [SystemMemory]
>>> [0001]                          Bit Width : 08
>>> [0001]                         Bit Offset : 00
>>> [0001]               Encoded Access Width : 01 [Byte Access:8]
>>> [0008]                            Address : 000000001c020000
>>>
>>> [0001]                     Interrupt Type : 08
>>> [0001]                PCAT-compatible IRQ : 00
>>> [0004]                          Interrupt : 0000006C
>>> [0001]                          Baud Rate : 07
>>> [0001]                             Parity : 00
>>> [0001]                          Stop Bits : 01
>>> [0001]                       Flow Control : 00
>>> [0001]                      Terminal Type : 00
>>> [0001]                           Reserved : 00
>>>
>>> The actual structure is longer, but you get the idea. I first map this
>>> to the correct Device in the DSDT with a device_initcall that will find
>>> the table then walk the ACPI namespace to find the corresponding device.
>>> This is stashed so that later we can perform the same kind of comparison
>>> that you do with DT today. I also populate options, though so far have
>>> only bothered to implement baud rate.
>>
>> I would recommend that you set up as many of these ASAP. Otherwise
>> someone's certain to mess up a table and we can never add them later.
> 
> So this is why I'm doing this (and other annoying things) right now - to
> make sure that vendors shipping platforms have valid data we can also
> use. If we wait until later, we'll have systems that potentially do the
> wrong thing. The table above is an example of one for the Mustang. I had
> the revision bumped to 2 and the IRQ information added to the reference
> one, and I've also verified the tables for Seattle, as well as "other"
> hardware that is in the pipeline from other vendors.
> 
>> Otherwise, sounds good!
> 
> So I'm handing this to Torez Smith to followup on (please keep her
> copied on replies to this thread). I'm attaching a *hack* patch I put
> together to proof of concept and then Torez will make this into
> something actually useable/upstreamable (without hard coded static baud
> strings and the like that I used to hack it up).

The Serial Port Console Redirection (SPCR) Table is patented by
Microsoft (spec and patent notice downloadable here
https://msdn.microsoft.com/en-us/library/windows/hardware/dn639132(v=vs.85).aspx )
and covered under the Microsoft Community Promise here
http://www.microsoft.com/openspecifications/en/us/programs/community-promise/default.aspx

The Micosoft Community Promise does not look compatible with GPL 2;
or more specifically, whomever eventually submitted the patch would likely not
be able to meet the criteria set forth by the Developer's Certificate of Origin 1.1
in Documentation/SubmittingPatches

Regards,
Peter Hurley
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