Re: [PATCH v2 2/2] nvmem: Add Apple eFuse driver

[Krzysztof Kozlowski]

On 06/03/2022 13:18, Sven Peter wrote:
> Apple SoCs contain eFuses used to store factory-programmed data such
> as calibration values for the PCIe or the Type-C PHY. They are organized
> as 32bit values exposed as MMIO.
> 
> Signed-off-by: Sven Peter <sven@xxxxxxxxxxxxx>
> ---
> v1 -> v2:
>   - fixed sparse warning about __iomem by introducing
>     struct apple_efuses_priv as done in other nvmem drivers
>   - make sure the driver actually works as a module by
>     setting .owner to THIS_MODULE and adding MODULE_DEVICE_TABLE
>     pointed out by Joey Gouly
> 
>  MAINTAINERS                  |  1 +
>  drivers/nvmem/Kconfig        | 12 ++++++
>  drivers/nvmem/Makefile       |  2 +
>  drivers/nvmem/apple-efuses.c | 82 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 97 insertions(+)
>  create mode 100644 drivers/nvmem/apple-efuses.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f70d8525cbd4..e3e973a3f651 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1781,6 +1781,7 @@ F:	drivers/i2c/busses/i2c-pasemi-core.c
>  F:	drivers/i2c/busses/i2c-pasemi-platform.c
>  F:	drivers/irqchip/irq-apple-aic.c
>  F:	drivers/mailbox/apple-mailbox.c
> +F:	drivers/nvmem/apple-efuses.c
>  F:	drivers/pinctrl/pinctrl-apple-gpio.c
>  F:	drivers/soc/apple/*
>  F:	drivers/watchdog/apple_wdt.c
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index da414617a54d..bba29d1aec96 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -300,4 +300,16 @@ config NVMEM_BRCM_NVRAM
>  	  This driver provides support for Broadcom's NVRAM that can be accessed
>  	  using I/O mapping.
>  
> +config NVMEM_APPLE_EFUSES
> +	tristate "Apple eFuse support"
> +	depends on ARCH_APPLE || COMPILE_TEST
> +	default ARCH_APPLE
> +	help
> +	  Say y here to enable support for reading eFuses on Apple SoCs
> +	  such as the M1. These are e.g. used to store factory programmed
> +	  calibration data required for the PCIe or the USB-C PHY.
> +
> +	  This driver can also be built as a module. If so, the module will
> +	  be called nvmem-apple-efuses.
> +
>  endif
> diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
> index dcbbde35b6a8..1a8e54691d3e 100644
> --- a/drivers/nvmem/Makefile
> +++ b/drivers/nvmem/Makefile
> @@ -61,3 +61,5 @@ obj-$(CONFIG_NVMEM_RMEM) 	+= nvmem-rmem.o
>  nvmem-rmem-y			:= rmem.o
>  obj-$(CONFIG_NVMEM_BRCM_NVRAM)	+= nvmem_brcm_nvram.o
>  nvmem_brcm_nvram-y		:= brcm_nvram.o
> +obj-$(CONFIG_NVMEM_APPLE_EFUSES)	+= nvmem-apple-efuses.o
> +nvmem-apple-efuses-y 		:= apple-efuses.o
> diff --git a/drivers/nvmem/apple-efuses.c b/drivers/nvmem/apple-efuses.c
> new file mode 100644
> index 000000000000..dd5576ec5408
> --- /dev/null
> +++ b/drivers/nvmem/apple-efuses.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Apple SoC eFuse driver
> + *
> + * Copyright (C) The Asahi Linux Contributors
> + */
> +
> +#include <linux/io.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/nvmem-provider.h>
> +#include <linux/platform_device.h>
> +
> +struct apple_efuses_priv {
> +	void __iomem *fuses;
> +};
> +
> +static int apple_efuses_read(void *context, unsigned int offset, void *val,
> +			     size_t bytes)
> +{
> +	struct apple_efuses_priv *priv = context;
> +	u32 *dst = val;
> +
> +	while (bytes >= sizeof(u32)) {
> +		*dst++ = readl_relaxed(priv->fuses + offset);
> +		bytes -= sizeof(u32);
> +		offset += sizeof(u32);
> +	}
> +
> +	return 0;
> +}
> +
> +static int apple_efuses_probe(struct platform_device *pdev)
> +{
> +	struct apple_efuses_priv *priv;
> +	struct resource *res;
> +	struct nvmem_config config = {
> +		.dev = &pdev->dev,
> +		.read_only = true,
> +		.reg_read = apple_efuses_read,
> +		.stride = sizeof(u32),
> +		.word_size = sizeof(u32),
> +		.name = "apple_efuses_nvmem",
> +		.id = NVMEM_DEVID_AUTO,
> +		.owner = THIS_MODULE,
> +		.root_only = true,
> +	};
> +
> +	priv = devm_kzalloc(config.dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->fuses = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
> +	if (IS_ERR(priv->fuses))
> +		return PTR_ERR(priv->fuses);
> +
> +	config.priv = priv;
> +	config.size = resource_size(res);
> +
> +	return PTR_ERR_OR_ZERO(devm_nvmem_register(config.dev, &config));
> +}
> +
> +static const struct of_device_id apple_efuses_of_match[] = {
> +	{ .compatible = "apple,efuses", },
> +	{}
> +};
> +
> +MODULE_DEVICE_TABLE(of, apple_efuses_of_match);
> +
> +static struct platform_driver apple_efuses_driver = {
> +	.driver = {
> +		.name = "apple_efuses",
> +		.of_match_table = apple_efuses_of_match,
> +		.owner = THIS_MODULE,

You wrote it also in changelog, but why do you need it? Doesn't core set
it? Coccinelle should complain about this as well.

Best regards,
Krzysztof