Re: [PATCH v3 2/2] RISC-V: Clean up the Zicbom block size probing

[Nathan Chancellor <nathan@kernel.org>]

On Tue, Sep 06, 2022 at 09:45:09AM +0200, Andrew Jones wrote:
> From: Palmer Dabbelt <palmer@rivosinc.com>
> 
> This fixes two issues: I truncated the warning's hart ID when porting to
> the 64-bit hart ID code, and the original code's warning handling could
> fire on an uninitialized hart ID.
> 
> The biggest change here is that riscv_cbom_block_size is no longer
> initialized, as IMO the default isn't sane: there's nothing in the ISA
> that mandates any specific cache block size, so falling back to one will
> just silently produce the wrong answer on some systems.  This also
> changes the probing order so the cache block size is known before
> enabling Zicbom support.
> 
> Fixes: 3aefb2ee5bdd ("riscv: implement Zicbom-based CMO instructions + the t-head variant")
> Fixes: 1631ba1259d6 ("riscv: Add support for non-coherent devices using zicbom extension")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> [Rebased on Anup's move patch and applied Conor Dooley's and Heiko
>  Stuebner's changes.]
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>

I can confirm that that the second issue appears to be resolved, as I
no longer see the instance of -Wsometimes-initialized from clang:

https://github.com/ClangBuiltLinux/linux/issues/1689

Build-tested-by: Nathan Chancellor <nathan@kernel.org>

Hopefully this can be queued up for 6.0.

> ---
>  arch/riscv/errata/thead/errata.c |  1 +
>  arch/riscv/kernel/setup.c        |  2 +-
>  arch/riscv/mm/cacheflush.c       | 21 +++++++++++----------
>  arch/riscv/mm/dma-noncoherent.c  |  2 ++
>  4 files changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
> index 202c83f677b2..96648c176f37 100644
> --- a/arch/riscv/errata/thead/errata.c
> +++ b/arch/riscv/errata/thead/errata.c
> @@ -37,6 +37,7 @@ static bool errata_probe_cmo(unsigned int stage,
>  	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
>  		return false;
>  
> +	riscv_cbom_block_size = L1_CACHE_BYTES;
>  	riscv_noncoherent_supported();
>  	return true;
>  #else
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 95ef6e2bf45c..2dfc463b86bb 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -296,8 +296,8 @@ void __init setup_arch(char **cmdline_p)
>  	setup_smp();
>  #endif
>  
> -	riscv_fill_hwcap();
>  	riscv_init_cbom_blocksize();
> +	riscv_fill_hwcap();
>  	apply_boot_alternatives();
>  }
>  
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 336c5deea870..e5b087be1577 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -89,39 +89,40 @@ void flush_icache_pte(pte_t pte)
>  }
>  #endif /* CONFIG_MMU */
>  
> -unsigned int riscv_cbom_block_size = L1_CACHE_BYTES;
> +unsigned int riscv_cbom_block_size;
>  
>  #ifdef CONFIG_RISCV_ISA_ZICBOM
>  void riscv_init_cbom_blocksize(void)
>  {
>  	struct device_node *node;
> +	unsigned long cbom_hartid;
> +	u32 val, probed_block_size;
>  	int ret;
> -	u32 val;
>  
> +	probed_block_size = 0;
>  	for_each_of_cpu_node(node) {
>  		unsigned long hartid;
> -		int cbom_hartid;
>  
>  		ret = riscv_of_processor_hartid(node, &hartid);
>  		if (ret)
>  			continue;
>  
> -		if (hartid < 0)
> -			continue;
> -
>  		/* set block-size for cbom extension if available */
>  		ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
>  		if (ret)
>  			continue;
>  
> -		if (!riscv_cbom_block_size) {
> -			riscv_cbom_block_size = val;
> +		if (!probed_block_size) {
> +			probed_block_size = val;
>  			cbom_hartid = hartid;
>  		} else {
> -			if (riscv_cbom_block_size != val)
> -				pr_warn("cbom-block-size mismatched between harts %d and %lu\n",
> +			if (probed_block_size != val)
> +				pr_warn("cbom-block-size mismatched between harts %lu and %lu\n",
>  					cbom_hartid, hartid);
>  		}
>  	}
> +
> +	if (probed_block_size)
> +		riscv_cbom_block_size = probed_block_size;
>  }
>  #endif
> diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> index 3f502a1a68b1..d919efab6eba 100644
> --- a/arch/riscv/mm/dma-noncoherent.c
> +++ b/arch/riscv/mm/dma-noncoherent.c
> @@ -74,5 +74,7 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  
>  void riscv_noncoherent_supported(void)
>  {
> +	WARN(!riscv_cbom_block_size,
> +	     "Non-coherent DMA support enabled without a block size\n");
>  	noncoherent_supported = true;
>  }
> -- 
> 2.37.2
> 

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