Re: [PATCH 4/6] riscv: mm: pass noncoherent or not to riscv_noncoherent_supported()

[Conor Dooley <conor.dooley@microchip.com>]

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Hey Jisheng,

On Sat, May 27, 2023 at 12:59:56AM +0800, Jisheng Zhang wrote:
> We will soon take different actions by checking the HW is noncoherent
> or not, I.E ZICBOM/ERRATA_THEAD_CMO or not.
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  arch/riscv/errata/thead/errata.c    | 19 +++++++++++--------
>  arch/riscv/include/asm/cacheflush.h |  4 ++--
>  arch/riscv/kernel/setup.c           |  6 +++++-
>  arch/riscv/mm/dma-noncoherent.c     | 10 ++++++----
>  4 files changed, 24 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index be84b14f0118..c192b80a5166 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -36,21 +36,24 @@ static bool errata_probe_pbmt(unsigned int stage,
>  static bool errata_probe_cmo(unsigned int stage,
>  			     unsigned long arch_id, unsigned long impid)
>  {
> -	if (!IS_ENABLED(CONFIG_ERRATA_THEAD_CMO))
> -		return false;
> -
> -	if (arch_id != 0 || impid != 0)
> -		return false;
> +	bool cmo;
>  
>  	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
>  		return false;
>  
> +	if (IS_ENABLED(CONFIG_ERRATA_THEAD_CMO) &&
> +	    (arch_id == 0 && impid == 0))
> +		cmo = true;
> +	else
> +		cmo = false;
> +
>  	if (stage == RISCV_ALTERNATIVES_BOOT) {
> -		riscv_cbom_block_size = L1_CACHE_BYTES;
> -		riscv_noncoherent_supported();
> +		if (cmo)
> +			riscv_cbom_block_size = L1_CACHE_BYTES;
> +		riscv_noncoherent_supported(cmo);
>  	}
>  
> -	return true;
> +	return cmo;

I don't really understand the changes that you are making to this
function, so that is tries really hard to call
riscv_noncoherent_supported(). Why do we need to always call the function
in the erratum's probe function, if the erratum is not detected, given
that riscv_noncoherent_supported() is called immediately after
apply_boot_alternatives() in setup_arch()?

>  }
>  
>  static bool errata_probe_pmu(unsigned int stage,
> diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> index 8091b8bf4883..9d056c9b625a 100644
> --- a/arch/riscv/include/asm/cacheflush.h
> +++ b/arch/riscv/include/asm/cacheflush.h
> @@ -54,9 +54,9 @@ extern unsigned int riscv_cboz_block_size;
>  void riscv_init_cbo_blocksizes(void);
>  
>  #ifdef CONFIG_RISCV_DMA_NONCOHERENT
> -void riscv_noncoherent_supported(void);
> +void riscv_noncoherent_supported(bool cmo);

I think it would "read better" if you renamed this variable to
"have_cmo".

>  #else
> -static inline void riscv_noncoherent_supported(void) {}
> +static inline void riscv_noncoherent_supported(bool cmo) {}
>  #endif
>  
>  /*
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 36b026057503..565f3e20169b 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -264,6 +264,7 @@ static void __init parse_dtb(void)
>  
>  void __init setup_arch(char **cmdline_p)
>  {
> +	bool cmo;
>  	parse_dtb();
>  	setup_initial_init_mm(_stext, _etext, _edata, _end);
>  
> @@ -298,7 +299,10 @@ void __init setup_arch(char **cmdline_p)
>  	apply_boot_alternatives();
>  	if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) &&
>  	    riscv_isa_extension_available(NULL, ZICBOM))
> -		riscv_noncoherent_supported();
> +		cmo = true;
> +	else
> +		cmo = false;
> +	riscv_noncoherent_supported(cmo);

As a nit, could you put a newline before the call to
riscv_noncoherent_supported()?

>  }
>  
>  static int __init topology_init(void)
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> index d51a75864e53..0e172e2b4751 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -72,9 +72,11 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  	dev->dma_coherent = coherent;
>  }
>  
> -void riscv_noncoherent_supported(void)
> +void riscv_noncoherent_supported(bool cmo)
>  {
> -	WARN(!riscv_cbom_block_size,
> -	     "Non-coherent DMA support enabled without a block size\n");
> -	noncoherent_supported = true;
> +	if (cmo) {
> +		WARN(!riscv_cbom_block_size,
> +		     "Non-coherent DMA support enabled without a block size\n");
> +		noncoherent_supported = true;
> +	}

The other places that we do a WARN() because of screwed up devicetrees
for CMO things, we do a WARN_TAINT(CPU_OUT_OF_SPEC). Should we do the
same here too?

Cheers,
Conor.

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