linux-kernel - Re: [PATCH v6 13/13] riscv: Add qspinlock support

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Message-ID: <90533aa9-186a-4f75-b3c5-d93d6682056b@ghiti.fr>
Date: Thu, 28 Nov 2024 15:50:09 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Conor Dooley <conor.dooley@...rochip.com>, Will Deacon <will@...nel.org>
Cc: Alexandre Ghiti <alexghiti@...osinc.com>, Jonathan Corbet
 <corbet@....net>, Paul Walmsley <paul.walmsley@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Andrea Parri <parri.andrea@...il.com>, Nathan Chancellor
 <nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Waiman Long <longman@...hat.com>,
 Boqun Feng <boqun.feng@...il.com>, Arnd Bergmann <arnd@...db.de>,
 Leonardo Bras <leobras@...hat.com>, Guo Ren <guoren@...nel.org>,
 linux-doc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-arch@...r.kernel.org
Subject: Re: [PATCH v6 13/13] riscv: Add qspinlock support

On 28/11/2024 15:14, Conor Dooley wrote:
> On Thu, Nov 28, 2024 at 01:41:36PM +0000, Will Deacon wrote:
>> On Thu, Nov 28, 2024 at 12:56:55PM +0000, Conor Dooley wrote:
>>> On Sun, Nov 03, 2024 at 03:51:53PM +0100, Alexandre Ghiti wrote:
>>>> In order to produce a generic kernel, a user can select
>>>> CONFIG_COMBO_SPINLOCKS which will fallback at runtime to the ticket
>>>> spinlock implementation if Zabha or Ziccrse are not present.
>>>>
>>>> Note that we can't use alternatives here because the discovery of
>>>> extensions is done too late and we need to start with the qspinlock
>>>> implementation because the ticket spinlock implementation would pollute
>>>> the spinlock value, so let's use static keys.
>>>>
>>>> This is largely based on Guo's work and Leonardo reviews at [1].
>>>>
>>>> Link: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@kernel.org/ [1]
>>>> Signed-off-by: Guo Ren <guoren@...nel.org>
>>>> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
>>> This patch (now commit ab83647fadae2 ("riscv: Add qspinlock support"))
>>> breaks boot on polarfire soc. It dies before outputting anything to the
>>> console. My .config has:
>>>
>>> # CONFIG_RISCV_TICKET_SPINLOCKS is not set
>>> # CONFIG_RISCV_QUEUED_SPINLOCKS is not set
>>> CONFIG_RISCV_COMBO_SPINLOCKS=y
>> I pointed out some of the fragility during review:
>>
>> https://lore.kernel.org/all/20241111164259.GA20042@willie-the-truck/
>>
>> so I'm kinda surprised it got merged tbh :/
> Maybe it could be reverted rather than having a broken boot with the
> default settings in -rc1.

No need to rush before we know what's happening,I guess you bisected to 
this commit right?

I don't have this soc, so can you provide $stval/$sepc/$scause, a 
config, a kernel, anything?

Does the polarfire soc provide Ziccrse?

>
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> linux-riscv@...ts.infradead.org
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