Re: [PATCH v2 2/2] ARM: implement cacheinfo support

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 14.10.2024 15:55, Dmitry Baryshkov wrote:
> On ARMv7 / v7m machines read CTR and CLIDR registers to provide
> information regarding the cache topology. Earlier machines should
> describe full cache topology in the device tree.
>
> Note, this follows the ARM64 cacheinfo support and provides only minimal
> support required to bootstrap cache info. All useful properties should
> be decribed in Device Tree.
>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---
>   arch/arm/Kconfig             |   1 +
>   arch/arm/include/asm/cache.h |   6 ++
>   arch/arm/kernel/Makefile     |   1 +
>   arch/arm/kernel/cacheinfo.c  | 173 +++++++++++++++++++++++++++++++++++++++++++
>   include/linux/cacheinfo.h    |   2 +-
>   5 files changed, 182 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 749179a1d162..e790543c3eaf 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -5,6 +5,7 @@ config ARM
>   	select ARCH_32BIT_OFF_T
>   	select ARCH_CORRECT_STACKTRACE_ON_KRETPROBE if HAVE_KRETPROBES && FRAME_POINTER && !ARM_UNWIND
>   	select ARCH_HAS_BINFMT_FLAT
> +	select ARCH_HAS_CACHE_LINE_SIZE if OF
>   	select ARCH_HAS_CPU_CACHE_ALIASING
>   	select ARCH_HAS_CPU_FINALIZE_INIT if MMU
>   	select ARCH_HAS_CURRENT_STACK_POINTER
> diff --git a/arch/arm/include/asm/cache.h b/arch/arm/include/asm/cache.h
> index e3ea34558ada..ecbc100d22a5 100644
> --- a/arch/arm/include/asm/cache.h
> +++ b/arch/arm/include/asm/cache.h
> @@ -26,4 +26,10 @@
>   
>   #define __read_mostly __section(".data..read_mostly")
>   
> +#ifndef __ASSEMBLY__
> +#ifdef CONFIG_ARCH_HAS_CACHE_LINE_SIZE
> +int cache_line_size(void);
> +#endif
> +#endif
> +
>   #endif
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index aaae31b8c4a5..b3333d070390 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -40,6 +40,7 @@ obj-y		+= entry-armv.o
>   endif
>   
>   obj-$(CONFIG_MMU)		+= bugs.o
> +obj-$(CONFIG_OF)		+= cacheinfo.o
>   obj-$(CONFIG_CPU_IDLE)		+= cpuidle.o
>   obj-$(CONFIG_ISA_DMA_API)	+= dma.o
>   obj-$(CONFIG_FIQ)		+= fiq.o fiqasm.o
> diff --git a/arch/arm/kernel/cacheinfo.c b/arch/arm/kernel/cacheinfo.c
> new file mode 100644
> index 000000000000..a8eabcaa18d8
> --- /dev/null
> +++ b/arch/arm/kernel/cacheinfo.c
> @@ -0,0 +1,173 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + *  ARM cacheinfo support
> + *
> + *  Copyright (C) 2023 Linaro Ltd.
> + *  Copyright (C) 2015 ARM Ltd.
> + *  All Rights Reserved
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/cacheinfo.h>
> +#include <linux/of.h>
> +
> +#include <asm/cachetype.h>
> +#include <asm/cputype.h>
> +#include <asm/system_info.h>
> +
> +/* Ctypen, bits[3(n - 1) + 2 : 3(n - 1)], for n = 1 to 7 */
> +#define CLIDR_CTYPE_SHIFT(level)	(3 * (level - 1))
> +#define CLIDR_CTYPE_MASK(level)		(7 << CLIDR_CTYPE_SHIFT(level))
> +#define CLIDR_CTYPE(clidr, level)	\
> +	(((clidr) & CLIDR_CTYPE_MASK(level)) >> CLIDR_CTYPE_SHIFT(level))
> +
> +#define MAX_CACHE_LEVEL			7	/* Max 7 level supported */
> +
> +#define CTR_FORMAT_MASK	GENMASK(27, 24)
> +#define CTR_FORMAT_ARMV6 0
> +#define CTR_FORMAT_ARMV7 4
> +#define CTR_CWG_MASK	GENMASK(27, 24)
> +#define CTR_DSIZE_LEN_MASK GENMASK(13, 12)
> +#define CTR_ISIZE_LEN_MASK GENMASK(1, 0)
> +
> +/* Also valid for v7m */
> +static inline int cache_line_size_cp15(void)
> +{
> +	u32 ctr = read_cpuid_cachetype();
> +	u32 format = FIELD_GET(CTR_FORMAT_MASK, ctr);
> +

On Samsung Exynos421x (CortexA9 based) format is read as 0x3, which 
causes a warning later in the code. How such value should be handled to 
avoid warning?

> +	if (format == CTR_FORMAT_ARMV7) {
> +		u32 cwg = FIELD_GET(CTR_CWG_MASK, ctr);
> +
> +		return cwg ? 4 << cwg : ARCH_DMA_MINALIGN;
> +	} else if (WARN_ON_ONCE(format != CTR_FORMAT_ARMV6)) {
> +		return ARCH_DMA_MINALIGN;
> +	}
> +
> +	return 8 << max(FIELD_GET(CTR_ISIZE_LEN_MASK, ctr),
> +			FIELD_GET(CTR_DSIZE_LEN_MASK, ctr));
> +}
> +

> >...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland