[PATCH V11 10/17] riscv: qspinlock: errata: Enable qspinlock for T-HEAD processors

[Leonardo Bras]

On Sun, Sep 10, 2023 at 04:29:04AM -0400, guoren at kernel.org wrote:
> From: Guo Ren <guoren at linux.alibaba.com>
> 
> According to qspinlock requirements, RISC-V gives out a weak LR/SC
> forward progress guarantee which does not satisfy qspinlock. But
> many vendors could produce stronger forward guarantee LR/SC to
> ensure the xchg_tail could be finished in time on any kind of
> hart. T-HEAD is the vendor

nit: "a vendor"

> which implements strong forward
> guarantee LR/SC instruction pairs, so enable qspinlock for T-HEAD
> with errata init help.
> 
> Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren at kernel.org>
> ---
>  arch/riscv/errata/thead/errata.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 751eb5a7f614..0df6a67302c0 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -86,6 +86,13 @@ static bool errata_probe_write_once(unsigned int stage,
>  	return false;
>  }
>  
> +extern bool enable_qspinlock_key;

Oh, now I understand why it was not static before. :)


> +static void errata_probe_qspinlock(unsigned int stage)
> +{
> +	if (stage == RISCV_ALTERNATIVES_BOOT)
> +		enable_qspinlock_key = true;
> +}
> +
>  static u32 thead_errata_probe(unsigned int stage,
>  			      unsigned long archid, unsigned long impid)
>  {
> @@ -103,6 +110,8 @@ static u32 thead_errata_probe(unsigned int stage,
>  	if (errata_probe_write_once(stage, archid, impid))
>  		cpu_req_errata |= BIT(ERRATA_THEAD_WRITE_ONCE);
>  
> +	errata_probe_qspinlock(stage);
> +
>  	return cpu_req_errata;
>  }
>  

So, if THEAD then enable qspinlock().

LGTM:
Reviewed-by: Leonardo Bras <leobras at redhat.com>

> -- 
> 2.36.1
>