linux-kernel - Re: [PATCH] ARM: bcm2835_defconfig: add minimal support for Raspberry Pi4

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Date:   Fri, 14 Feb 2020 16:14:23 +0100
From:   "Nicolas Saenz Julienne" <nsaenzjulienne@...e.de>
To:     "Marek Szyprowski" <m.szyprowski@...sung.com>,
        "Stefan Wahren" <stefan.wahren@...e.com>,
        <linux-rpi-kernel@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: bcm2835_defconfig: add minimal support for
 Raspberry Pi4

On Fri Feb 14, 2020 at 1:25 PM, Marek Szyprowski wrote:
> Hi Stefan,
>
> On 13.02.2020 10:59, Stefan Wahren wrote:
> > On 13.02.20 08:35, Marek Szyprowski wrote:
> >> On 12.02.2020 19:31, Nicolas Saenz Julienne wrote:
> >>> On Wed, 2020-02-12 at 11:20 +0100, Marek Szyprowski wrote:
> >>>> Add drivers for the minimal set of devices needed to boot Raspberry Pi4
> >>>> board.
> >>>>
> >>>> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> >>> Just so you know, the amount of support on the RPi4 you might be able to get
> >>> updating bcm2835_defconfig's config is very limited. Only 1GB of ram and no
> >>> PCIe (so no USBs).
> >> Yes, I know. A lots of core features is missing: SMP, HIGHMEM, LPAE, PCI
> >> and so on, but having a possibility to boot RPi4 with this defconfig
> >> increases the test coverage.
> > in case you want to increase test coverage, we better enable all
> > Raspberry Pi 4 relevant hardware parts (hwrng, thermal, PCI ...). This
> > is what we did for older Pi boards.
>
> Okay, I will add thermal in v2. HWRNG is already selected as module.
> Enabling PCI without LPAE makes no sense as the driver won't be able to
> initialize properly.

Agree on this.

> > SMP, HIGHMEM, LPAE are different and shouldn't be enabled in
> > bcm2835_defconfig from my PoV.
>
> Maybe it would make sense to also add bcm2711_defconfig or
> bcm2835_lpae_defconfig?

IMO bcm2711_defconfig if the last resort solution. I don't think you can
do bcm2835_lpae_defconfig as RPi and RPi2 SoCs don't support LPAE. An
intemediate solution is being discussed here:
https://lkml.org/lkml/2020/1/10/694

Regards,
Nicolas