linux-kernel - Re: [PATCH v3 0/5] arm64: Initial Realtek RTD1295 enablement

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Message-ID: <95ea400d-4605-10f4-fa5f-f554b4705d58@suse.de>
Date:   Tue, 5 Sep 2017 10:46:08 +0200
From:   Andreas Färber <afaerber@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, Roc He <hepeng@...oo.tv>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        蒋丽琴 <jiang.liqin@...iatech.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v3 0/5] arm64: Initial Realtek RTD1295 enablement

Am 05.09.2017 um 09:18 schrieb Arnd Bergmann:
> On Tue, Sep 5, 2017 at 12:09 AM, Andreas Färber <afaerber@...e.de> wrote:
>> Am 14.05.2017 um 04:24 schrieb Andreas Färber:
>>> This mini-series adds initial support for the Realtek RTD1295 SoC and
>>> the Zidoo X9S TV box.
>>>
>>> v3 changes #address-cells, #size-cells and ranges.
>>>
>>> With these patches CPU0 can be booted with earlycon.
>>>
>>> PSCI doesn't work despite present in the vendor device tree; as enable-method
>>> it instead used a custom "rtk-spin-table" that I sadly have no source code of.
>>
>> Synology has now published source code for RTD1293/1296. This has
>> allowed me to narrow the RTD1295 CPU1..3 issue down to two changes in
>> arch/arm64/kernel/smp_spin_table.c:smp_spin_table_cpu_prepare():
>>
>> 1) writel_relaxed() instead of writeq_relaxed()
>> 2) ioremap() instead of ioremap_cache()
>>
>> Without those changes it hangs in earlycon after this line:
>> [    0.043674] Mountpoint-cache hash table entries: 4096 (order: 3,
>> 32768 bytes)
>>
>> The size difference sounds easy enough - we could introduce an optional
>> cpu-release-size property to handle this or derive a "spin-table-32bit"
>> enable-method to that effect.
>>
>> The second one appears to be caused by PROT_NORMAL vs.
>> PROT_DEVICE_nGnRE. Is there any simple check we could do on
>> cpu-release-addr to choose which MT to use?
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=113954c6463d1d80a206e91627ae49711f8b47cd
>>
>> Any other ideas?
> 
> I think we had a similar problem before and concluded that something
> requiring a write into an MMIO register is simply not a spin-table
> implementation but something else.

Well, my understanding was that "something else" is not acceptable for
arm64. And still being without ATF, U-Boot and OP-TEE sources I don't
see how I could reimplement PSCI instead.

> Is this simply using a copy of the spin-table code to trigger the actual
> booting of the secondary CPU?

Yes. Realtek have duplicated and modified the file - I've instead tried
to reuse the existing code with those minimal changes, for a chance to
get this mainline with suitable conditions.

The only other Realtek changes are additions for cpu_disable/cpu_die
that I am ignoring for now. Happy that the cores are finally up!

> Can you identify the MMIO address?

The magic 32-bit register is 0x9801aa44, with RAM being 0..0x80000000.

Thus I was hoping there might be some handy is_ram_addr(phys_addr) that
we could use in generic code to choose the right ioremap function.

Regards,
Andreas

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