linux-kernel - Re: [PATCH 1/2] arm64: kernel: Add SMC Session ID to results

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Message-ID: <20160823103841.GD8724@red-moon>
Date:   Tue, 23 Aug 2016 11:38:41 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Stephen Boyd <sboyd@...eaurora.org>
Cc:     Will Deacon <will.deacon@....com>,
        Andy Gross <andy.gross@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        stanimir.varbanov@...aro.org, linux-kernel@...r.kernel.org,
        patches@...aro.org, Bjorn Andersson <bjorn.andersson@...aro.org>,
        sudeep.holla@....com
Subject: Re: [PATCH 1/2] arm64: kernel: Add SMC Session ID to results

On Mon, Aug 22, 2016 at 05:38:31PM -0700, Stephen Boyd wrote:

[...]

> This all comes about because the firmware generates a session id
> for the SMC call and jams it in x6. The assembly on the
> non-secure side is written with a tight loop around the smc
> instruction so that when the return value indicates
> "interrupted", x6 is kept intact and the non-secure OS can jump
> back to the secure OS without register reloading. Perhaps
> referring to x6 as result value is not correct because it's
> really a session id that's irrelevant once the smc call
> completes.

Sorry I missed this bit. The session id is _generated_ by secure
firmware (probably only when the value passed in x6 == 0 (?))
and actually returned to the caller so that subsequent (interrupted)
calls can re-issue the same value, is that correct ?

If that's the case the value in x6 is a result value from an SMCCC
perspective and your current FW is not SMCCC compliant.

Lorenzo