linux-kernel - Re: [PATCH v4 07/24] EDAC/amd64: Define function to dehash address

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Date:   Fri, 11 Feb 2022 23:47:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yazen Ghannam <yazen.ghannam@....com>
Cc:     linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        mchehab@...nel.org, tony.luck@...el.com, james.morse@....com,
        rric@...nel.org, Smita.KoralahalliChannabasappa@....com
Subject: Re: [PATCH v4 07/24] EDAC/amd64: Define function to dehash address

On Thu, Jan 27, 2022 at 08:40:58PM +0000, Yazen Ghannam wrote:
> Move the dehashing code into a separate helper function. Define a
> DF2-specific function for the current code. Specific helper functions
> will be added for future DF versions.
> 
> The dehashing function used is based on the interleaving mode rather
> than the Data Fabric version. So save the function pointer in the
> context struct. The use of "df2" in the name of the current function is
> only because the interleaving mode using it only appears on Data Fabric
> 2 systems.
> 
> Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> ---
> Link:
> https://lore.kernel.org/r/20211028175728.121452-12-yazen.ghannam@amd.com
> 
> v3->v4:
> * Include pr_debug() on failure.
> 
> v2->v3:
> * Was patch 12 in v2.
> 
> v1->v2:
> * Moved from arch/x86 to EDAC.
> * Add new function pointer in ctx struct.
> 
>  drivers/edac/amd64_edac.c | 36 +++++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/edac/amd64_edac.c b/drivers/edac/amd64_edac.c
> index 350204eadb27..da2d0d9ce406 100644
> --- a/drivers/edac/amd64_edac.c
> +++ b/drivers/edac/amd64_edac.c
> @@ -1077,7 +1077,7 @@ struct addr_ctx {
>  	u8 map_num;
>  	u8 intlv_addr_bit;
>  	u8 cs_id;
> -	bool hash_enabled;
> +	int (*dehash_addr)(struct addr_ctx *ctx);

A function pointer in a context struct?!

> @@ -1357,18 +1372,9 @@ static int umc_normaddr_to_sysaddr(u64 norm_addr, u16 nid, u8 umc, u64 *sys_addr
>  		goto out_err;
>  	}
>  
> -	if (ctx.hash_enabled) {
> -		/* Save some parentheses and grab ls-bit at the end. */
> -		hashed_bit =	(ctx.ret_addr >> 12) ^
> -				(ctx.ret_addr >> 18) ^
> -				(ctx.ret_addr >> 21) ^
> -				(ctx.ret_addr >> 30) ^
> -				ctx.cs_id;
> -
> -		hashed_bit &= BIT(0);
> -
> -		if (hashed_bit != ((ctx.ret_addr >> ctx.intlv_addr_bit) & BIT(0)))
> -			ctx.ret_addr ^= BIT(ctx.intlv_addr_bit);
> +	if (ctx.dehash_addr && ctx.dehash_addr(&ctx)) {

So you can just as well do:

	if (ctx->intlv_mode == 8)
		dehash_addr();

And dehash_addr() can inside determine whether df2 or df3.

Btw, that 8 looks like magic. It should be a #define.

What you have now looks a bit weird with those function pointers lumped
together with those other members of addr_ctx. Dunno, maybe it'll make
more sense when I read the rest first...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette