Re: [PATCH v1 0/9] Fix Allwinner D1 boot regression

From: Thomas Gleixner <tglx@linutronix.de>
To: Samuel Holland <samuel.holland@sifive.com>,
	Emil Renner Berthing <emil.renner.berthing@canonical.com>,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	Anup Patel <apatel@ventanamicro.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Daniel Lezcano <daniel.lezcano@linaro.org>
Subject: Re: [PATCH v1 0/9] Fix Allwinner D1 boot regression
Date: Thu, 15 Aug 2024 16:11:14 +0200	[thread overview]
Message-ID: <87h6blnaf1.ffs@tglx> (raw)
In-Reply-To: <686d61c4-e7ac-4dca-a7fd-decdd72e84d9@sifive.com>

On Thu, Aug 15 2024 at 08:32, Samuel Holland wrote:
> On 2024-08-15 8:16 AM, Thomas Gleixner wrote:
>> Yes. So the riscv timer is not working on this thing or it stops
>> somehow.
>
> That's correct. With the (firmware) devicetree that Emil is using, the OpenSBI
> firmware does not have a timer device, so it does not expose the (optional[1])
> SBI time extension, and sbi_set_timer() does nothing.

Sigh. Does RISCV really have to repeat all mistakes which have been made
by x86, ARM and others before? It's known for decades that the kernel
relies on a working timer...

> I wrote a patch (not submitted) to skip registering riscv_clock_event when the
> SBI time extension is unavailable, but this doesn't fully solve the issue
> either, because then we have no clockevent at all when
> check_unaligned_access_all_cpus() is called.

check_unaligned_access_all_cpus() is irrelevant.

> How early in the boot process are we "required" to have a functional clockevent?
> Do we need to refactor check_unaligned_access_all_cpus() so it works on systems
> where the only clockevent is provided by a platform device?

Right after init/main::late_time_init() everything can depend on a
working timer and on jiffies increasing.

I'm actually surprised that the boot process gets that far. That's just
by pure luck, really.

Thanks,

        tglx

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