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

From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Shawn Guo <shawnguo@kernel.org>
Cc: Marek Vasut <marex@denx.de>, Jan Kiszka <jan.kiszka@siemens.com>,
	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: Mon, 16 Nov 2020 11:10:04 +0200	[thread overview]
Message-ID: <20201116091004.GC6540@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20201010002854.GB27426@pendragon.ideasonboard.com>

Hi Shawn,

On Sat, Oct 10, 2020 at 03:28:55AM +0300, Laurent Pinchart wrote:
> 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.

Ping. Could we get this merged ?

-- 
Regards,

Laurent Pinchart

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