linux-kernel - Re: [PATCH v1] gpio: keystone: add dsp gpio controller driver

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Date:	Thu, 24 Jul 2014 23:42:47 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Suman Anna <s-anna@...com>,
	Alexander Shiyan <shc_work@...l.ru>,
	Alexandre Courbot <gnurou@...il.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	ivan.khoronzhuk@...com,
	Muralidharan Karicheri <m-karicheri2@...com>,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] gpio: keystone: add dsp gpio controller driver

On 24 July 2014 22:52, Santosh Shilimkar <santosh.shilimkar@...com> wrote:
> On Thursday 24 July 2014 01:19 PM, Jassi Brar wrote:
>> On 23 July 2014 20:40, Linus Walleij <linus.walleij@...aro.org> wrote:
>>> On Wed, Jul 16, 2014 at 12:43 PM, Grygorii Strashko
>>> <grygorii.strashko@...com> wrote:
>>>
>>>> From: Murali Karicheri <m-karicheri2@...com>
>>>>
>>>> On Keystone SOCs, ARM host can send interrupts to DSP cores using the
>>>> DSP GPIO controller IP. Each DSP GPIO controller provides 28 IRQ signals for
>>>> each DSP core. This is one of the component used by the IPC mechanism used
>>>> on Keystone SOCs.
>>>>
>>>> Keystone 2 DSP GPIO controller has specific features:
>>>> - each GPIO can be configured only as output pin;
>>>> - setting GPIO value to 1 causes IRQ generation on target DSP core;
>>>> - reading pin value returns 0 - if IRQ was handled or 1 - IRQ is still
>>>>   pending.
>>>>
>>>> Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>>
>>> Pardon me. How is this GENERAL PURPOSE Input/Output?
>>>
>>> It seems very very much SPECIAL PURPOSE to me, it's like
>>> you're just shoehorning some IPC mechanism into the GPIO
>>> subsystem, and this may be because the datasheet calls it
>>> GPIO when it's not.
>>>
>>> What other stuff than DSP is connected to these lines, and is it
>>> really even external lines? Aren't these just polysilicon rails
>>> pretty much hammered to be used by the DSP and nothing else.
>>>
>>> What is the difference between this and a mailbox IRQ line
>>> and the kind of stuff handled by drivers/mailbox?
>>>
>>> I'd like Suman and Jassi to have a look at this to see if it's
>>> actually a mailbox before we proceed.
>>>
>> The controller seems like most others, only incapable of reading
>> signals (output only).
>>  The userspace driving those signals to communicate with a DSP isn't
>> enough to call it a mailbox usecase, because on a different board the
>> userspace may drive those signals to control LEDs :)
>>
> Exactly !!
> And that was my point. Thanks for echo.
>
Yeah but if the AP and DSP are within the same package (i.e, the
'pins' can't be used for any other purpose on any board), one might
sell it as a mailbox. However, since the mailbox protocol driver would
be in userspace, I think it is justified to expose that as GPIO
otherwise we'll have to add another interface for userspace to control
the DSP.

Cheers,
Jassi
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