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

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Message-ID: <20241128-uncivil-removed-4e105d1397c9@wendy>
Date: Thu, 28 Nov 2024 14:14:53 +0000
From: Conor Dooley <conor.dooley@...rochip.com>
To: 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 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.

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