Re: [PATCH RFC v2 0/2] hwspinlock: Introduce raw capability for hwspinlock_device

From: Lina Iyer <lina.iyer@linaro.org>
To: Ohad Ben-Cohen <ohad@wizery.com>
Cc: Andy Gross <agross@codeaurora.org>,
	Bjorn Andersson <bjorn.andersson@sonymobile.com>,
	Jeffrey Hugo <jhugo@codeaurora.org>,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC v2 0/2] hwspinlock: Introduce raw capability for hwspinlock_device
Date: Fri, 14 Aug 2015 07:52:32 -0600	[thread overview]
Message-ID: <20150814135232.GB86880@linaro.org> (raw)
In-Reply-To: <CAK=WgbZdO==vmDNh5=E=th9+O_08aUtXSn5hy=kEgja9-GikGg@mail.gmail.com>

On Fri, Aug 14 2015 at 04:52 -0600, Ohad Ben-Cohen wrote:
>On Thu, Aug 13, 2015 at 6:25 PM, Andy Gross <agross@codeaurora.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".
>
Absolutely.

>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?
>
Yes, the number is hardcoded in the SPM power controller driver. It
explicitly requests Lock #7

-- Lina