[PATCH v6 13/13] riscv: Add qspinlock support

[Will Deacon]

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 at kernel.org>
> > Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.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 :/

Will