linux-kernel - Re: [PATCH 2/4] nvmem: add generic driver for devices with MMIO access

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Message-ID: <88a8c2ef-8478-84b3-e4c9-6d3760313241@linaro.org>
Date:   Wed, 1 Feb 2023 11:52:52 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Rafał Miłecki <zajec5@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH 2/4] nvmem: add generic driver for devices with MMIO
 access



On 01/02/2023 06:47, Rafał Miłecki wrote:
> From: Rafał Miłecki <rafal@...ecki.pl>
> 
> With nvmem layouts in place we should now work on plain content access
> NVMEM drivers (e.g. MMIO one). Actual NVMEM content handling should go
> to layout drivers.
> 
> Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
> ---
>   drivers/nvmem/Kconfig  | 10 ++++++
>   drivers/nvmem/Makefile |  2 ++
>   drivers/nvmem/mmio.c   | 80 ++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 92 insertions(+)
>   create mode 100644 drivers/nvmem/mmio.c
> 
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index 789729ff7e50..9eb5e93f0455 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -170,6 +170,16 @@ config NVMEM_MICROCHIP_OTPC
>   	  This driver enable the OTP controller available on Microchip SAMA7G5
>   	  SoCs. It controls the access to the OTP memory connected to it.
>   
> +config NVMEM_MMIO
> +	tristate "MMIO access based NVMEM support"
> +	depends on HAS_IOMEM
> +	help
> +	  This driver provides support for NVMEM devices that can be accessed
> +	  using MMIO.
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called nvmem-mmio.
> +
>   config NVMEM_MTK_EFUSE
>   	tristate "Mediatek SoCs EFUSE support"
>   	depends on ARCH_MEDIATEK || COMPILE_TEST
> diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
> index 442f9a4876a5..2f2bed7cdf24 100644
> --- a/drivers/nvmem/Makefile
> +++ b/drivers/nvmem/Makefile
> @@ -36,6 +36,8 @@ obj-$(CONFIG_NVMEM_MESON_MX_EFUSE)	+= nvmem_meson_mx_efuse.o
>   nvmem_meson_mx_efuse-y			:= meson-mx-efuse.o
>   obj-$(CONFIG_NVMEM_MICROCHIP_OTPC)	+= nvmem-microchip-otpc.o
>   nvmem-microchip-otpc-y			:= microchip-otpc.o
> +obj-$(CONFIG_NVMEM_MMIO)		+= nvmem-mmio.o
> +nvmem-mmio-y				:= mmio.o
>   obj-$(CONFIG_NVMEM_MTK_EFUSE)		+= nvmem_mtk-efuse.o
>   nvmem_mtk-efuse-y			:= mtk-efuse.o
>   obj-$(CONFIG_NVMEM_MXS_OCOTP)		+= nvmem-mxs-ocotp.o
> diff --git a/drivers/nvmem/mmio.c b/drivers/nvmem/mmio.c
> new file mode 100644
> index 000000000000..19c8880dc675
> --- /dev/null
> +++ b/drivers/nvmem/mmio.c
> @@ -0,0 +1,80 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2023 Rafał Miłecki <rafal@...ecki.pl>
> + */
> +
> +#include <linux/io.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/nvmem-provider.h>
> +#include <linux/platform_device.h>
> +#include <linux/property.h>
> +#include <linux/slab.h>
> +
> +struct mmio_nvmem {
> +	void __iomem *base;
> +};
> +
> +static int mmio_nvmem_read(void *context, unsigned int offset, void *val, size_t bytes)
> +{
> +	struct mmio_nvmem *priv = context;
> +
> +	memcpy_fromio(val, priv->base, bytes);

How does this work with different register strides?

> +
> +	return 0;
> +}
> +
> +static int mmio_nvmem_probe(struct platform_device *pdev)
> +{
> +	struct nvmem_config config = {
> +		.name = "mmio-nvmem",


you could use NVMEM_DEVID_AUTO.


But this is not great, this is going to break the existing abi for 
converted drivers. Either we find a way to pass compatible specific data 
and override the default values.

Also there are going to be cases where access to registers will require 
additional resources like clks or pd.


--srini

> +		.read_only = true,
> +		.reg_read = mmio_nvmem_read,
> +	};
> +	struct device *dev = &pdev->dev;
> +	struct mmio_nvmem *priv;
> +	struct resource *res;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	priv->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
> +	if (IS_ERR(priv->base))
> +		return PTR_ERR(priv->base);
> +
> +	config.dev = dev;
> +	config.size = resource_size(res);
> +	config.word_size = sizeof(u8);
> +	config.stride = sizeof(u8);
> +	config.priv = priv;
> +
> +	if (!device_property_present(dev, "read-only"))
> +		dev_warn(dev, "Writing is not supported yet");
> +
> +	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
> +}
> +
> +static const struct of_device_id mmio_nvmem_of_match_table[] = {
> +	{ .compatible = "mmio-nvmem", },
> +	{},
> +};
> +
> +static struct platform_driver mmio_nvmem_driver = {
> +	.probe = mmio_nvmem_probe,
> +	.driver = {
> +		.name = "mmio_nvmem",
> +		.of_match_table = mmio_nvmem_of_match_table,
> +	},
> +};
> +
> +static int __init mmio_nvmem_init(void)
> +{
> +	return platform_driver_register(&mmio_nvmem_driver);
> +}
> +
> +subsys_initcall_sync(mmio_nvmem_init);
> +
> +MODULE_AUTHOR("Rafał Miłecki");
> +MODULE_LICENSE("GPL");
> +MODULE_DEVICE_TABLE(of, mmio_nvmem_of_match_table);