linux-kernel - Re: [PATCH net-next V6] net/mlx5: Improve write-combining test reliability for ARM64 Grace CPUs

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Message-ID: <651ee9fe-706e-4471-a71b-e7a12b42cc3e@redhat.com>
Date: Wed, 1 Oct 2025 11:28:09 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Tariq Toukan <tariqt@...dia.com>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Mark Bloch <mbloch@...dia.com>, netdev@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
 Gal Pressman <gal@...dia.com>, Leon Romanovsky <leonro@...dia.com>,
 Jason Gunthorpe <jgg@...dia.com>, Michael Guralnik <michaelgur@...dia.com>,
 Moshe Shemesh <moshe@...dia.com>, Will Deacon <will@...nel.org>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
 "H. Peter Anvin" <hpa@...or.com>, Justin Stitt <justinstitt@...gle.com>,
 linux-s390@...r.kernel.org, llvm@...ts.linux.dev,
 Ingo Molnar <mingo@...hat.com>, Bill Wendling <morbo@...gle.com>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>,
 Salil Mehta <salil.mehta@...wei.com>, Sven Schnelle <svens@...ux.ibm.com>,
 Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
 Yisen Zhuang <yisen.zhuang@...wei.com>, Arnd Bergmann <arnd@...db.de>,
 Leon Romanovsky <leonro@...lanox.com>, linux-arch@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, Mark Rutland <mark.rutland@....com>,
 Michael Guralnik <michaelgur@...lanox.com>, patches@...ts.linux.dev,
 Niklas Schnelle <schnelle@...ux.ibm.com>, Jijie Shao <shaojijie@...wei.com>,
 Simon Horman <horms@...nel.org>, Patrisious Haddad <phaddad@...dia.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, Eric Dumazet <edumazet@...gle.com>,
 Catalin Marinas <catalin.marinas@....com>, Jakub Kicinski <kuba@...nel.org>,
 "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next V6] net/mlx5: Improve write-combining test
 reliability for ARM64 Grace CPUs

Hi,

On 9/28/25 11:08 PM, Tariq Toukan wrote:
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/wc.c b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
> index 999d6216648a..c281153bd411 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/wc.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
> @@ -7,6 +7,10 @@
>  #include "mlx5_core.h"
>  #include "wq.h"
>  
> +#if IS_ENABLED(CONFIG_KERNEL_MODE_NEON) && IS_ENABLED(CONFIG_ARM64)
> +#include <asm/neon.h>
> +#endif
> +
>  #define TEST_WC_NUM_WQES 255
>  #define TEST_WC_LOG_CQ_SZ (order_base_2(TEST_WC_NUM_WQES))
>  #define TEST_WC_SQ_LOG_WQ_SZ TEST_WC_LOG_CQ_SZ
> @@ -255,6 +259,27 @@ static void mlx5_wc_destroy_sq(struct mlx5_wc_sq *sq)
>  	mlx5_wq_destroy(&sq->wq_ctrl);
>  }
>  
> +static void mlx5_iowrite64_copy(struct mlx5_wc_sq *sq, __be32 mmio_wqe[16],
> +				size_t mmio_wqe_size, unsigned int offset)
> +{
> +#if IS_ENABLED(CONFIG_KERNEL_MODE_NEON) && IS_ENABLED(CONFIG_ARM64)
> +	if (cpu_has_neon()) {
> +		kernel_neon_begin();
> +		asm volatile
> +		(".arch_extension simd;\n\t"

Here I'm observing build errors with aarch64-linux-gnu-gcc 12.1.1
20220507 (Red Hat Cross 12.1.1-1):

/tmp/cchqHdeI.s: Assembler messages:
/tmp/cchqHdeI.s:746: Error: unknown architectural extension `simd;'

I can't reproduce the error on any recent compiler version via
godbolt.org, so I *think* this should not block/be reverted for the MR,
but could you please have a look soonish?

Thanks,

Paolo