linux-kernel - Re: [PATCH RFC v2 0/2] hwspinlock: Introduce raw capability for hwspinlock

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Message-ID: <CAK=WgbZdO==vmDNh5=E=th9+O_08aUtXSn5hy=kEgja9-GikGg@mail.gmail.com>
Date:	Fri, 14 Aug 2015 13:52:28 +0300
From:	Ohad Ben-Cohen <ohad@...ery.com>
To:	Andy Gross <agross@...eaurora.org>
Cc:	Lina Iyer <lina.iyer@...aro.org>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>,
	Jeffrey Hugo <jhugo@...eaurora.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 0/2] hwspinlock: Introduce raw capability for hwspinlock_device

On Thu, Aug 13, 2015 at 6:25 PM, Andy Gross <agross@...eaurora.org> wrote:
> The issue in hardwiring this into the driver itself means forfeiting
> extensibility.  So on one side (w/ raw support), we get the ability to deal with
> the lock number changing.  On the other side (w/o raw), we'd have to probably
> tie this to chip compat to figure out which lock is the 'special' if it ever
> changes.

It sounds like the decision "which lock to use" is a separate problem
from "can it go raw".

If the hardware doesn't prohibit raw mode, then every lock can be used
in raw mode. So you just have to pick one and make sure both sides
know which lock you use --- which is a classic multi-processor
synchronization issue.

> It's arbitrary right now.  The remote processor selected a number, not the
> processor running Linux.

Is the number hardcoded right now? and you're using
hwspin_lock_request_specific on the Linux side to acquire the lock?
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