linux-kernel - Re: [PATCH v7 1/4] Documentation: dt: add common bindings for hwspinlock

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Date:	Mon, 2 Feb 2015 15:14:54 -0600
From:	Suman Anna <s-anna@...com>
To:	Ohad Ben-Cohen <ohad@...ery.com>, Bjorn Andersson <bjorn@...o.se>
CC:	Mark Rutland <mark.rutland@....com>,
	Rob Herring <robherring2@...il.com>,
	Kumar Gala <galak@...eaurora.org>,
	Josh Cartwright <joshc@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v7 1/4] Documentation: dt: add common bindings for hwspinlock

On 02/01/2015 05:00 AM, Ohad Ben-Cohen wrote:
> On Sat, Jan 31, 2015 at 7:41 AM, Ohad Ben-Cohen <ohad@...ery.com> wrote:
>> On Sat, Jan 31, 2015 at 1:29 AM, Bjorn Andersson <bjorn@...o.se> wrote:
>>> In a system where you have two hwlock blocks lckA and lckB, each
>>> consisting of 8 locks and you have dspB that can only access lckB
>>
>> This is a good example - thanks. To be able to cope with such cases we
>> will have to pass a hwlock block reference and its relative lock id.

So, you mean lckB is only between the host and dspB. Obviously, if it
were shared between dspA and dspB only, then the allocation and
management would be completely outside the host Linux driver's scope.

> 
> Additionally, to support such a scenario, we can no longer retain the
> simple dynamic allocation API we have today, because it might end up
> allocating dspB an hwlock from IckA.
> 
> We will have to make sure hwlocks are allocated only from pools
> visible to the user, something that will change not only the
> hwspinlock API but also the way it maintains the hwlocks.

Right, the current API definitely will not scale for that. It was
designed around the concept that it's easier to exchange a single global
id, rather than a lcbB:id or some other similar semantics that needs to
be interpreted.

> 
> I suspect we want to wait for such hardware to show up first, and only
> then add framework support for it. 

Agreed.

regards
Suman

> Regardless, we obviously do want to
> make sure our DT binding is prepared for the worse, so we'll drop the
> "base-id" field.
> 
> Thanks,
> Ohad.
> 

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