Re: [PATCH v2 17/22] soc: apple: Add hardware tunable support

[Alyssa Anne Rosenzweig <alyssa@rosenzweig.io>]

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>

Le Sat, Sep 06, 2025 at 03:43:30PM +0000, Sven Peter a écrit :
> Various hardware, like the Type-C PHY or the Thunderbolt/USB4 NHI,
> present on Apple SoCs need machine-specific tunables passed from our
> bootloader m1n1 to the device tree. Add generic helpers so that we
> don't have to duplicate this across multiple drivers.
> 
> Signed-off-by: Sven Peter <sven@kernel.org>
> ---
>  drivers/soc/apple/Kconfig         |  4 +++
>  drivers/soc/apple/Makefile        |  3 ++
>  drivers/soc/apple/tunable.c       | 71 +++++++++++++++++++++++++++++++++++++++
>  include/linux/soc/apple/tunable.h | 60 +++++++++++++++++++++++++++++++++
>  4 files changed, 138 insertions(+)
> 
> diff --git a/drivers/soc/apple/Kconfig b/drivers/soc/apple/Kconfig
> index 6388cbe1e56b5a9d90acad3ee2377ed6ac0d207d..f266b70fd9620cc940dc685f7eb2972c21a361df 100644
> --- a/drivers/soc/apple/Kconfig
> +++ b/drivers/soc/apple/Kconfig
> @@ -41,6 +41,10 @@ config APPLE_SART
>  
>  	  Say 'y' here if you have an Apple SoC.
>  
> +config APPLE_TUNABLE
> +	tristate
> +	depends on ARCH_APPLE || COMPILE_TEST
> +
>  endmenu
>  
>  endif
> diff --git a/drivers/soc/apple/Makefile b/drivers/soc/apple/Makefile
> index 4d9ab8f3037b7159771d8817fa507ba29f99ae10..0b85ab61aefe131349a67d0aa80204edd8e89925 100644
> --- a/drivers/soc/apple/Makefile
> +++ b/drivers/soc/apple/Makefile
> @@ -8,3 +8,6 @@ apple-rtkit-y = rtkit.o rtkit-crashlog.o
>  
>  obj-$(CONFIG_APPLE_SART) += apple-sart.o
>  apple-sart-y = sart.o
> +
> +obj-$(CONFIG_APPLE_TUNABLE) += apple-tunable.o
> +apple-tunable-y = tunable.o
> diff --git a/drivers/soc/apple/tunable.c b/drivers/soc/apple/tunable.c
> new file mode 100644
> index 0000000000000000000000000000000000000000..c54da8ef28cef16118c518c761f95e8dd9f78002
> --- /dev/null
> +++ b/drivers/soc/apple/tunable.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: GPL-2.0-only OR MIT
> +/*
> + * Apple Silicon hardware tunable support
> + *
> + * Each tunable is a list with each entry containing a offset into the MMIO
> + * region, a mask of bits to be cleared and a set of bits to be set. These
> + * tunables are passed along by the previous boot stages and vary from device
> + * to device such that they cannot be hardcoded in the individual drivers.
> + *
> + * Copyright (C) The Asahi Linux Contributors
> + */
> +
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/soc/apple/tunable.h>
> +
> +struct apple_tunable *devm_apple_tunable_parse(struct device *dev,
> +					       struct device_node *np,
> +					       const char *name)
> +{
> +	struct apple_tunable *tunable;
> +	struct property *prop;
> +	const __be32 *p;
> +	size_t sz;
> +	int i;
> +
> +	prop = of_find_property(np, name, NULL);
> +	if (!prop)
> +		return ERR_PTR(-ENOENT);
> +
> +	if (prop->length % (3 * sizeof(u32)))
> +		return ERR_PTR(-EINVAL);
> +	sz = prop->length / (3 * sizeof(u32));
> +
> +	tunable = devm_kzalloc(dev,
> +			       sizeof(*tunable) + sz * sizeof(*tunable->values),
> +			       GFP_KERNEL);
> +	if (!tunable)
> +		return ERR_PTR(-ENOMEM);
> +	tunable->sz = sz;
> +
> +	for (i = 0, p = NULL; i < tunable->sz; ++i) {
> +		p = of_prop_next_u32(prop, p, &tunable->values[i].offset);
> +		p = of_prop_next_u32(prop, p, &tunable->values[i].mask);
> +		p = of_prop_next_u32(prop, p, &tunable->values[i].value);
> +	}
> +
> +	return tunable;
> +}
> +EXPORT_SYMBOL(devm_apple_tunable_parse);
> +
> +void apple_tunable_apply(void __iomem *regs, struct apple_tunable *tunable)
> +{
> +	size_t i;
> +
> +	for (i = 0; i < tunable->sz; ++i) {
> +		u32 val, old_val;
> +
> +		val = old_val = readl_relaxed(regs + tunable->values[i].offset);
> +		val &= ~tunable->values[i].mask;
> +		val |= tunable->values[i].value;
> +		if (val != old_val)
> +			writel_relaxed(val, regs + tunable->values[i].offset);
> +	}
> +}
> +EXPORT_SYMBOL(apple_tunable_apply);
> +
> +MODULE_LICENSE("Dual MIT/GPL");
> +MODULE_AUTHOR("Sven Peter <sven@kernel.org>");
> +MODULE_DESCRIPTION("Apple Silicon hardware tunable support");
> diff --git a/include/linux/soc/apple/tunable.h b/include/linux/soc/apple/tunable.h
> new file mode 100644
> index 0000000000000000000000000000000000000000..3785ee2c898993328356005b63682f4848fc2f22
> --- /dev/null
> +++ b/include/linux/soc/apple/tunable.h
> @@ -0,0 +1,60 @@
> +/* SPDX-License-Identifier: GPL-2.0-only OR MIT */
> +/*
> + * Apple Silicon hardware tunable support
> + *
> + * Each tunable is a list with each entry containing a offset into the MMIO
> + * region, a mask of bits to be cleared and a set of bits to be set. These
> + * tunables are passed along by the previous boot stages and vary from device
> + * to device such that they cannot be hardcoded in the individual drivers.
> + *
> + * Copyright (C) The Asahi Linux Contributors
> + */
> +
> +#ifndef _LINUX_SOC_APPLE_TUNABLE_H_
> +#define _LINUX_SOC_APPLE_TUNABLE_H_
> +
> +#include <linux/device.h>
> +#include <linux/types.h>
> +
> +/**
> + * Struct to store an Apple Silicon hardware tunable.
> + *
> + * Each tunable is a list with each entry containing a offset into the MMIO
> + * region, a mask of bits to be cleared and a set of bits to be set. These
> + * tunables are passed along by the previous boot stages and vary from device
> + * to device such that they cannot be hardcoded in the individual drivers.
> + *
> + * @param sz Number of [offset, mask, value] tuples stored in values.
> + * @param values [offset, mask, value] array.
> + */
> +struct apple_tunable {
> +	size_t sz;
> +	struct {
> +		u32 offset;
> +		u32 mask;
> +		u32 value;
> +	} values[];
> +};
> +
> +/**
> + * Parse an array of hardware tunables from the device tree.
> + *
> + * @dev: Device node used for devm_kzalloc internally.
> + * @np: Device node which contains the tunable array.
> + * @name: Name of the device tree property which contains the tunables.
> + *
> + * @return: devres allocated struct on success or PTR_ERR on failure.
> + */
> +struct apple_tunable *devm_apple_tunable_parse(struct device *dev,
> +					       struct device_node *np,
> +					       const char *name);
> +
> +/**
> + * Apply a previously loaded hardware tunable.
> + *
> + * @param regs: MMIO to which the tunable will be applied.
> + * @param tunable: Pointer to the tunable.
> + */
> +void apple_tunable_apply(void __iomem *regs, struct apple_tunable *tunable);
> +
> +#endif
> 
> -- 
> 2.34.1
> 
>