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Date: Wed, 1 May 2024 12:31:15 -0700
From: Charlie Jenkins <charlie@rivosinc.com>
To: Evan Green <evan@rivosinc.com>
Cc: Conor Dooley <conor@kernel.org>, Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Samuel Holland <samuel@sholland.org>,
	Conor Dooley <conor.dooley@microchip.com>,
	=?iso-8859-1?Q?Cl=E9ment_L=E9ger?= <cleger@rivosinc.com>,
	Jonathan Corbet <corbet@lwn.net>, Shuah Khan <shuah@kernel.org>,
	linux-riscv@lists.infradead.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, Palmer Dabbelt <palmer@rivosinc.com>,
	linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
	linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 13/16] riscv: hwprobe: Add thead vendor extension
 probing
Message-ID: <ZjKYg0EGKq4nwSnp@ghost>
References: <20240426-dev-charlie-support_thead_vector_6_9-v4-0-5cf53b5bc492@rivosinc.com>
 <20240426-dev-charlie-support_thead_vector_6_9-v4-13-5cf53b5bc492@rivosinc.com>
 <CALs-HsuPXhc93jqs==-Gq5Os701jxmzjxg82EHdOFHn+H-9Jdg@mail.gmail.com>
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On Wed, May 01, 2024 at 09:46:00AM -0700, Evan Green wrote:
> On Fri, Apr 26, 2024 at 2:37 PM Charlie Jenkins <charlie@rivosinc.com> wrote:
> >
> > Add a new hwprobe key "RISCV_HWPROBE_KEY_VENDOR_EXT_THEAD_0" which
> > allows userspace to probe for the new RISCV_ISA_VENDOR_EXT_XTHEADVECTOR
> > vendor extension.
> >
> > This new key will allow userspace code to probe for which thead vendor
> > extensions are supported. This API is modeled to be consistent with
> > RISCV_HWPROBE_KEY_IMA_EXT_0. The bitmask returned will have each bit
> > corresponding to a supported thead vendor extension of the cpumask set.
> > Just like RISCV_HWPROBE_KEY_IMA_EXT_0, this allows a userspace program
> > to determine all of the supported thead vendor extensions in one call.
> >
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> >  arch/riscv/include/asm/hwprobe.h                   |  4 +--
> >  .../include/asm/vendor_extensions/thead_hwprobe.h  | 11 ++++++
> >  arch/riscv/include/uapi/asm/hwprobe.h              |  3 +-
> >  arch/riscv/include/uapi/asm/vendor/thead.h         |  3 ++
> >  arch/riscv/kernel/sys_hwprobe.c                    |  9 +++++
> >  arch/riscv/kernel/vendor_extensions/Makefile       |  1 +
> >  .../riscv/kernel/vendor_extensions/thead_hwprobe.c | 42 ++++++++++++++++++++++
> >  7 files changed, 70 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
> > index 630507dff5ea..e68496b4f8de 100644
> > --- a/arch/riscv/include/asm/hwprobe.h
> > +++ b/arch/riscv/include/asm/hwprobe.h
> > @@ -1,6 +1,6 @@
> >  /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> >  /*
> > - * Copyright 2023 Rivos, Inc
> > + * Copyright 2023-2024 Rivos, Inc
> >   */
> >
> >  #ifndef _ASM_HWPROBE_H
> > @@ -8,7 +8,7 @@
> >
> >  #include <uapi/asm/hwprobe.h>
> >
> > -#define RISCV_HWPROBE_MAX_KEY 6
> > +#define RISCV_HWPROBE_MAX_KEY 7
> >
> >  static inline bool riscv_hwprobe_key_is_valid(__s64 key)
> >  {
> > diff --git a/arch/riscv/include/asm/vendor_extensions/thead_hwprobe.h b/arch/riscv/include/asm/vendor_extensions/thead_hwprobe.h
> > new file mode 100644
> > index 000000000000..907cfc4eb4dc
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/vendor_extensions/thead_hwprobe.h
> > @@ -0,0 +1,11 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _ASM_RISCV_VENDOR_EXTENSIONS_THEAD_HWPROBE_H
> > +#define _ASM_RISCV_VENDOR_EXTENSIONS_THEAD_HWPROBE_H
> > +
> > +#include <linux/cpumask.h>
> > +
> > +#include <uapi/asm/hwprobe.h>
> > +
> > +void hwprobe_isa_vendor_ext_thead_0(struct riscv_hwprobe *pair, const struct cpumask *cpus);
> > +
> > +#endif
> > diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> > index 9f2a8e3ff204..21e96a63f9ea 100644
> > --- a/arch/riscv/include/uapi/asm/hwprobe.h
> > +++ b/arch/riscv/include/uapi/asm/hwprobe.h
> > @@ -1,6 +1,6 @@
> >  /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> >  /*
> > - * Copyright 2023 Rivos, Inc
> > + * Copyright 2023-2024 Rivos, Inc
> >   */
> >
> >  #ifndef _UAPI_ASM_HWPROBE_H
> > @@ -67,6 +67,7 @@ struct riscv_hwprobe {
> >  #define                RISCV_HWPROBE_MISALIGNED_UNSUPPORTED    (4 << 0)
> >  #define                RISCV_HWPROBE_MISALIGNED_MASK           (7 << 0)
> >  #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE    6
> > +#define RISCV_HWPROBE_KEY_VENDOR_EXT_THEAD_0   7
> >  /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
> >
> >  /* Flags */
> > diff --git a/arch/riscv/include/uapi/asm/vendor/thead.h b/arch/riscv/include/uapi/asm/vendor/thead.h
> > new file mode 100644
> > index 000000000000..43790ebe5faf
> > --- /dev/null
> > +++ b/arch/riscv/include/uapi/asm/vendor/thead.h
> > @@ -0,0 +1,3 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +
> > +#define                RISCV_HWPROBE_VENDOR_EXT_XTHEADVECTOR   (1 << 0)
> > diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
> > index 8cae41a502dd..e59cac545df5 100644
> > --- a/arch/riscv/kernel/sys_hwprobe.c
> > +++ b/arch/riscv/kernel/sys_hwprobe.c
> > @@ -13,6 +13,7 @@
> >  #include <asm/uaccess.h>
> >  #include <asm/unistd.h>
> >  #include <asm/vector.h>
> > +#include <asm/vendor_extensions/thead_hwprobe.h>
> >  #include <vdso/vsyscall.h>
> >
> >
> > @@ -216,6 +217,14 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
> >                         pair->value = riscv_cboz_block_size;
> >                 break;
> >
> > +       case RISCV_HWPROBE_KEY_VENDOR_EXT_THEAD_0:
> > +#ifdef CONFIG_RISCV_ISA_VENDOR_EXT_THEAD
> > +               hwprobe_isa_vendor_ext_thead_0(pair, cpus);
> > +#else
> > +               pair->value = 0;
> > +#endif
> 
> Could we move this ifdef into the header by declaring a dummy
> hwprobe_isa_vendor_ext_thead_0() in the header for the !ENABLED case?
> 
> > +               break;
> > +
> >         /*
> >          * For forward compatibility, unknown keys don't fail the whole
> >          * call, but get their element key set to -1 and value set to 0
> > diff --git a/arch/riscv/kernel/vendor_extensions/Makefile b/arch/riscv/kernel/vendor_extensions/Makefile
> > index 8f1c5a4dc38f..f511fd269e8a 100644
> > --- a/arch/riscv/kernel/vendor_extensions/Makefile
> > +++ b/arch/riscv/kernel/vendor_extensions/Makefile
> > @@ -1,4 +1,5 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> >
> >  obj-$(CONFIG_RISCV_ISA_VENDOR_EXT_THEAD)       += thead.o
> > +obj-$(CONFIG_RISCV_ISA_VENDOR_EXT_THEAD)       += thead_hwprobe.o
> >  obj-$(CONFIG_RISCV_ISA_VENDOR_EXT_ANDES)       += andes.o
> > diff --git a/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c b/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c
> > new file mode 100644
> > index 000000000000..e8e2de292032
> > --- /dev/null
> > +++ b/arch/riscv/kernel/vendor_extensions/thead_hwprobe.c
> > @@ -0,0 +1,42 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +
> > +#include <asm/vector.h>
> > +#include <asm/vendor_extensions/thead.h>
> > +#include <asm/vendor_extensions/thead_hwprobe.h>
> > +
> > +#include <linux/cpumask.h>
> > +#include <linux/types.h>
> > +
> > +#include <uapi/asm/hwprobe.h>
> > +#include <uapi/asm/vendor/thead.h>
> > +
> > +void hwprobe_isa_vendor_ext_thead_0(struct riscv_hwprobe *pair, const struct cpumask *cpus)
> > +{
> > +       /*
> > +        * Loop through and record extensions that 1) anyone has, and 2) anyone
> > +        * doesn't have.
> > +        */
> > +
> > +       struct riscv_isainfo *per_hart_thead_bitmap = riscv_isa_vendor_ext_list_thead.per_hart_vendor_bitmap;
> > +       int cpu;
> > +       u64 missing;
> > +
> > +       for_each_cpu(cpu, cpus) {
> > +               struct riscv_isainfo *isainfo = &per_hart_thead_bitmap[cpu];
> > +
> > +#define EXT_KEY(ext)                                                                   \
> > +       do {                                                                            \
> > +               if (__riscv_isa_extension_available(isainfo->isa, RISCV_ISA_VENDOR_EXT_##ext)) \
> > +                       pair->value |= RISCV_HWPROBE_VENDOR_EXT_##ext;                  \
> > +               else                                                                    \
> > +                       missing |= RISCV_HWPROBE_VENDOR_EXT_##ext;                      \
> > +       } while (false)
> > +
> > +       EXT_KEY(XTHEADVECTOR);
> > +
> > +#undef EXT_KEY
> > +       }
> > +
> > +       /* Now turn off reporting features if any CPU is missing it. */> +       pair->value &= ~missing;
> > +}
> 
> Something to consider, perhaps when there's a second vendor, is how we
> might reduce this boilerplate on the second vendor. Probably best to
> wait though until we know exactly what the commonalities are. This
> looks good for now.
> 

Yes it should be mostly identical on second vendor. I think the only
difference would be "per_hart_thead_bitmap" and the list of extensions.
I can probably factor this out a bit.

- Charlie

> 
> >
> > --
> > 2.44.0
> >