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

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Date:	Thu, 24 Jul 2014 22:49:56 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	Suman Anna <s-anna@...com>,
	Alexander Shiyan <shc_work@...l.ru>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	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 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 :)

Cheers,
Jassi
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