From: Mark Rutland <mark.rutland@arm•com>
To: Vladimir Murzin <vladimir.murzin@arm•com>
Cc: linux-arm-kernel@lists•infradead.org, kvmarm@lists•linux.dev,
broonie@kernel•org, catalin.marinas@arm•com, james.morse@arm•com,
maz@kernel•org, oupton@kernel•org, tabba@google•com,
will@kernel•org
Subject: Re: [PATCH 17/18] arm64: fpsimd: Move SME save/restore inline
Date: Tue, 26 May 2026 17:38:40 +0100 [thread overview]
Message-ID: <ahXMkPEpgaZQf_Nk@J2N7QTR9R3> (raw)
In-Reply-To: <ahW8Eba3SNqfVDdk@J2N7QTR9R3>
On Tue, May 26, 2026 at 04:28:17PM +0100, Mark Rutland wrote:
> On Tue, May 26, 2026 at 03:39:56PM +0100, Vladimir Murzin wrote:
> > Hi Mark,
> >
> > On 5/26/26 15:08, Mark Rutland wrote:
> > > On Thu, May 21, 2026 at 02:25:55PM +0100, Mark Rutland wrote:
> > >> +static inline void __sme_save_za(struct sme_state *state, unsigned long svl)
> > >> +{
> > >> + /* The <Wv> argument to STR (array vector) can only encode W12-W15 */
> > >> + register unsigned long v asm ("12");
> > > Sorry, I had meant to put "x12" here, but evidently GCC and LLVM accept
> > > "12" on its own.
> > >
> > > For clarity (e.g. to match the comment) I'll change that to "w12" and
> > > make the type unsigned int. Likewise in __sme_load_za().
> >
> > I suspect you are intentionally not using "Ucj" constrain to limit register allocator,
> > if so I'm wondering why?
>
> Thanks for the suggestion; that was ignorance rather than intent.
>
> I was not aware of "Ucj" as it doesn't appear on the public GCC
> documentation:
>
> https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html
>
> Looking at the machine description file, that's marked with '@internal',
> so IIUC GCC folk don't seem to expect/want people to use it. That said,
> LLVM seems to support it.
>
> I'll go check that all relevant toolchains support this, and poke GCC
> folk to see if they're happy to promote that to a public constraint.
GCC folk seem happy to make this public, which is great! I'll cross-link
a thread here if/when patches appear.
In the short term, using "Ucj" would require bumping our minimum
supported toolchain necessary for SME:
* GCC gained "Ucj" in 14.1.0, tagged on 7 May 2024.
* LLVM gained "Ucj" in 18.1.0, tagged on 27 Feb 2024.
... so using that would require adding a dependency on a newer
toolchain, e.g. via a CC_HAS_UCJ_CONSTRAINT to match the existing
CC_HAS_K_CONSTRAINT.
Aligned with the rationale on patch 8, v6.16 (tagged 27 July 2025) was
contemporary with GCC 15.1.0 (tagged 25 April 2025) and LLVM 20.1.0
(tagged 4 March 2025), both of which supported "Ucj".
> If that's all good, I'll move over to "Ucj". If not, I'll update the
> commit message and/or comments to explain why.
If Will and Catalin are happy to depend on a toolchain as above, I'll go
add the necessary CC_HAS_UCJ_CONSTRAINT Kconfig logic.
Otherwise I'll go note the above in a comment, and stick with the
register variable for now.
Mark.
next prev parent reply other threads:[~2026-05-26 16:39 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 13:25 [PATCH 00/18] arm64+KVM: FPSIMD/SVE/SME cleanups Mark Rutland
2026-05-21 13:25 ` [PATCH 01/18] KVM: arm64: Don't include <asm/fpsimdmacros.h> Mark Rutland
2026-05-26 14:18 ` Mark Brown
2026-05-27 10:10 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 02/18] KVM: arm64: Don't override FFR save/restore argument Mark Rutland
2026-05-26 14:27 ` Mark Brown
2026-05-27 10:16 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 03/18] KVM: arm64: pkvm: Save host FPMR in host cpu context Mark Rutland
2026-05-27 10:29 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 04/18] KVM: arm64: pkvm: Remove struct cpu_sve_state Mark Rutland
2026-05-27 11:58 ` Vladimir Murzin
2026-05-27 16:02 ` Mark Rutland
2026-05-27 16:11 ` Vladimir Murzin
2026-05-28 15:09 ` Mark Rutland
2026-05-28 15:12 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 05/18] arm64: fpsimd: Fold sve_init_regs() into do_sve_acc() Mark Rutland
2026-05-26 15:28 ` Mark Brown
2026-05-27 12:05 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 06/18] arm64: fpsimd: Remove sve_set_vq() and sme_set_vq() Mark Rutland
2026-05-26 15:42 ` Mark Brown
2026-05-27 12:50 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 07/18] arm64: fpsimd: Use assembler for SVE instructions Mark Rutland
2026-05-26 15:43 ` Mark Brown
2026-05-27 12:58 ` Vladimir Murzin
2026-05-27 16:10 ` Mark Rutland
2026-05-21 13:25 ` [PATCH 08/18] arm64: fpsimd: Use assembler for baseline SME instructions Mark Rutland
2026-05-26 15:45 ` Mark Brown
2026-05-27 13:06 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 09/18] arm64: fpsimd: Move sve_get_vl() and sme_get_vl() inline Mark Rutland
2026-05-26 15:47 ` Mark Brown
2026-05-27 13:18 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 10/18] arm64: sysreg: Add FPCR and FPSR Mark Rutland
2026-05-26 15:55 ` Mark Brown
2026-05-26 16:51 ` Mark Rutland
2026-05-26 16:54 ` Mark Brown
2026-05-21 13:25 ` [PATCH 11/18] arm64: fpsimd: Split FPSR/FPCR from SVE save/restore Mark Rutland
2026-05-26 16:28 ` Mark Brown
2026-05-27 13:51 ` Mark Rutland
2026-05-27 14:13 ` Mark Brown
2026-05-27 16:13 ` Mark Rutland
2026-05-27 13:44 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 12/18] arm64: fpsimd: Move fpsimd save/restore inline Mark Rutland
2026-05-26 16:44 ` Mark Brown
2026-05-28 16:15 ` Mark Rutland
2026-05-28 16:39 ` Mark Brown
2026-05-27 14:49 ` Vladimir Murzin
2026-05-27 15:34 ` Mark Rutland
2026-05-27 16:13 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 13/18] arm64: fpsimd: Use opaque type for SVE state Mark Rutland
2026-05-26 16:53 ` Mark Brown
2026-05-28 9:45 ` Vladimir Murzin
2026-05-28 16:25 ` Mark Rutland
2026-05-21 13:25 ` [PATCH 14/18] arm64: fpsimd: Use opaque type for SME state Mark Rutland
2026-05-26 16:56 ` Mark Brown
2026-05-28 9:51 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 15/18] arm64: fpsimd: Move SVE save/restore inline Mark Rutland
2026-05-27 12:29 ` Mark Brown
2026-05-28 10:39 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 16/18] arm64: fpsimd: Move sve_flush_live() inline Mark Rutland
2026-05-27 12:54 ` Mark Brown
2026-05-27 16:23 ` Mark Rutland
2026-05-28 10:49 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 17/18] arm64: fpsimd: Move SME save/restore inline Mark Rutland
2026-05-26 14:08 ` Mark Rutland
2026-05-26 14:39 ` Vladimir Murzin
2026-05-26 15:28 ` Mark Rutland
2026-05-26 16:38 ` Mark Rutland [this message]
2026-05-27 9:00 ` Vladimir Murzin
2026-05-29 9:10 ` Mark Rutland
2026-05-28 12:30 ` Vladimir Murzin
2026-05-28 14:39 ` Mark Rutland
2026-05-21 13:25 ` [PATCH 18/18] arm64: fpsimd: Remove <asm/fpsimdmacros.h> Mark Rutland
2026-05-28 13:10 ` Vladimir Murzin
2026-05-27 8:07 ` [PATCH 00/18] arm64+KVM: FPSIMD/SVE/SME cleanups Marc Zyngier
2026-05-27 10:32 ` Mark Rutland
2026-05-27 14:36 ` Will Deacon
2026-05-28 13:21 ` Vladimir Murzin
2026-05-28 16:28 ` Mark Rutland
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