linux-kernel - Re: [PATCH 2/2] ARC: mm: fix new code about cache aliasing

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Date: Thu, 28 Mar 2024 09:57:07 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Vineet Gupta <vgupta@...nel.org>, linux-snps-arc@...ts.infradead.org,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 2/2] ARC: mm: fix new code about cache aliasing

On 2024-03-28 01:39, Vineet Gupta wrote:
> Manual/partial revert of 8690bbcf3b70 ("Introduce cpu_dcache_is_aliasing() across all architectures")
> 
> Current generation of ARCv2/ARCv3 based HSxx cores are only PIPT (to software
> at least).
> 
> Legacy ARC700 cpus could be VIPT aliasing (based on cache geometry and
> PAGE_SIZE) however recently that support was ripped out so VIPT aliasing
> cache is not relevant to ARC anymore.
> 
> P.S. : This has been discussed a few times on lists [1]
> P.S.2: Please CC the arch maintainers and/or mailing list before adding
>         such interfaces.

Because 8690bbcf3b70 was introducing a tree-wide change affecting all
architectures, I CC'd linux-arch@...r.kernel.org. I expected all
architecture maintainers to follow that list, which is relatively
low volume.

I'm sorry that you learn about this after the fact as a result.
My intent was to use the list rather than CC about 50 additional
people/mailing lists.

Of course, if VIPT aliasing is removed from ARC, removing the
config ARCH_HAS_CPU_CACHE_ALIASING and using the generic
cpu_dcache_is_aliasing() is the way to go. Feel free to add
my:

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Thanks,

Mathieu


> 
> [1] http://lists.infradead.org/pipermail/linux-snps-arc/2023-February/006899.html
> 
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Signed-off-by: Vineet Gupta <vgupta@...nel.org>
> ---
>   arch/arc/Kconfig                 | 1 -
>   arch/arc/include/asm/cachetype.h | 9 ---------
>   2 files changed, 10 deletions(-)
>   delete mode 100644 arch/arc/include/asm/cachetype.h
> 
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index 99d2845f3feb..4092bec198be 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -6,7 +6,6 @@
>   config ARC
>   	def_bool y
>   	select ARC_TIMERS
> -	select ARCH_HAS_CPU_CACHE_ALIASING
>   	select ARCH_HAS_CACHE_LINE_SIZE
>   	select ARCH_HAS_DEBUG_VM_PGTABLE
>   	select ARCH_HAS_DMA_PREP_COHERENT
> diff --git a/arch/arc/include/asm/cachetype.h b/arch/arc/include/asm/cachetype.h
> deleted file mode 100644
> index 05fc7ed59712..000000000000
> --- a/arch/arc/include/asm/cachetype.h
> +++ /dev/null
> @@ -1,9 +0,0 @@
> -/* SPDX-License-Identifier: GPL-2.0 */
> -#ifndef __ASM_ARC_CACHETYPE_H
> -#define __ASM_ARC_CACHETYPE_H
> -
> -#include <linux/types.h>
> -
> -#define cpu_dcache_is_aliasing()	true
> -
> -#endif

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com