Re: [RFC PATCH 0/5] Add smp booting support for Qualcomm ARMv8 SoCs

From: Kumar Gala <galak@codeaurora.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	"linux-arm-msm@vger.kernel.org" <linux-arm-msm@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"abhimany@codeaurora.org" <abhimany@codeaurora.org>,
	Will Deacon <Will.Deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"arm@kernel.org" <arm@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC PATCH 0/5] Add smp booting support for Qualcomm ARMv8 SoCs
Date: Tue, 14 Apr 2015 14:49:04 -0500	[thread overview]
Message-ID: <07185B2C-3F37-4E70-9096-1EF5EA8D68CE@codeaurora.org> (raw)
In-Reply-To: <20150414163613.GM28709@leverpostej>

> On Apr 14, 2015, at 11:36 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> 
> On Fri, Apr 10, 2015 at 11:05:29AM +0100, Catalin Marinas wrote:
>> On Thu, Apr 09, 2015 at 12:37:06PM -0500, Kumar Gala wrote:
>>> This patch set adds support for SMP boot on the MSM8x16 family of Qualcomm SoCs.
>>> 
>>> To support SMP on the MSM8x16 SoCs we need to add ARMv8/64-bit SCM interfaces to
>>> setup the boot/release addresses for the secondary CPUs.  In addition we need
>>> a uniquie set of cpu ops.  I'm aware the desired methods for booting secondary
>>> CPUs is either via spintable or PSCI.  However, these SoCs are shipping with a
>>> firmware that does not support those methods.
>> 
>> And the reason is? Some guesses:
>> 
>> a) QC doesn't think boot interface (and cpuidle) standardisation is
>>   worth the effort (to put it nicely)
>> b) The hardware was available before we even mentioned PSCI
>> c) PSCI is not suitable for the QC's SCM interface
>> d) Any combination of the above
>> 
>> I strongly suspect it's point (a). Should we expect future QC hardware
>> to do the same?
>> 
>> You could argue the reason was (b), though we've been discussing PSCI
>> for at least two years and, according to QC press releases, MSM8916
>> started sampling in 2014.
>> 
>> The only valid reason is (c) and if that's the case, I would expect a
>> proposal for a new firmware interface protocol (it could be PSCI-based),
>> well documented, that can be shared with others that may encounter the
>> same shortcomings.
> 
> There's no need to even fork PSCI. The PSCI specification will evolve
> over time as vendors request changes and we try to accomodate them.
> 
> If there's something that PSCI doesn't do that you need it to, contact
> ARM. Other vendors already have.

But what is someone to do between the period of getting PSCI spec updated and needing to ship a product with firmware?

The take still sounds like if you don’t implement an exact version of PSCI you are screwed from being supported in the upstream ARM64 kernel.

- k

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