Re: [PATCH] [RFC] ARM: imx: add smp support for imx7d

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Marek Vasut <marex@denx.de>, Shawn Guo <shawnguo@kernel.org>,
	Arulpandiyan Vadivel <arulpandiyan_vadivel@mentor.com>,
	Anson Huang <b20788@freescale.com>,
	Leonard Crestez <leonard.crestez@nxp.com>,
	Fabio Estevam <festevam@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	NXP Linux Team <linux-imx@nxp.com>
Subject: Re: [PATCH] [RFC] ARM: imx: add smp support for imx7d
Date: Sat, 10 Oct 2020 03:28:54 +0300	[thread overview]
Message-ID: <20201010002854.GB27426@pendragon.ideasonboard.com> (raw)
In-Reply-To: <d0fed022-b0c0-d804-8a9c-ea17cc58e821@siemens.com>

Hello everybody,

On Tue, Sep 22, 2020 at 04:59:44PM +0200, Jan Kiszka wrote:
> On 22.09.20 13:34, Marek Vasut wrote:
> > On 9/22/20 8:27 AM, Shawn Guo wrote:
> >> On Tue, Sep 22, 2020 at 2:22 PM Shawn Guo <shawnguo@kernel.org> wrote:
> >>> On Thu, Sep 17, 2020 at 06:08:14PM +0200, Marek Vasut wrote:
> >>>> From: Anson Huang <b20788@freescale.com>
> >>>>
> >>>> Add SMP support for i.MX7D, including CPU hotplug support, for
> >>>> systems where TFA is not present.
> >>>
> >>> These systems are not supported by upstream kernel.  Sorry.
> >>
> >> I meant for systems without PSCI support actually.
> > 
> > Is there any specific reason for that ?
> > 
> > The SoC works fully well with mainline U-Boot and without TFA, except
> > the code for bringing up the second core is missing from mainline and
> > that is all that is missing. PSCI is unnecessary extra complexity here.
> 
> We are coming from vendor kernels and would like to base our products on 
> mainline for $countless-good-reasons. With the vendor kernels, this 
> "classic" way of booting worked fine, with historic bootloaders and also 
> with current mainline U-Boot.
> 
> If PSCI support is mandated, we would now be unable to migrate devices 
> in the field that should not or cannot receive a bootloader update 
> because existing deployments generally do not ship TF-A or any other 
> PSCI implementation on ARMv7 - there was mostly no use for it (and there 
> will likely be none, except for CPU onlining). Would be a shame.
> 
> So I'd also like to understand what speaks against a merge, provided 
> this patch does not break other cases or make the code significantly 
> more complex and harder to maintain.

I side with Marek and Jan on this. While PSCI is mandatory for ARM64
platforms (whether that's a good or bad thing is out of scope here),
there's no such requirement for ARMv7. Unless there was a decision to
migrate the whole or ARMv7 to PSCI, I see no reason to not merge this
patch.

-- 
Regards,

Laurent Pinchart

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