Date:   Tue, 30 Aug 2022 14:36:25 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Michael Walle <michael@...le.cc>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Rafał Miłecki <rafal@...ecki.pl>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Frank Rowand <frowand.list@...il.com>
Cc:     linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        netdev@...r.kernel.org, Ahmad Fatoum <a.fatoum@...gutronix.de>
Subject: Re: [PATCH v1 06/14] nvmem: core: introduce NVMEM layouts



On 25/08/2022 22:44, Michael Walle wrote:
> NVMEM layouts are used to generate NVMEM cells during runtime. Think of
> an EEPROM with a well-defined conent. For now, the content can be
> described by a device tree or a board file. But this only works if the
> offsets and lengths are static and don't change. One could also argue
> that putting the layout of the EEPROM in the device tree is the wrong
> place. Instead, the device tree should just have a specific compatible
> string.
> 
> Right now there are two use cases:
>   (1) The NVMEM cell needs special processing. E.g. if it only specifies
>       a base MAC address offset and you need to add an offset, or it
>       needs to parse a MAC from ASCII format or some proprietary format.
>       (Post processing of cells is added in a later commit).
>   (2) u-boot environment parsing. The cells don't have a particular
>       offset but it needs parsing the content to determine the offsets
>       and length.
> 
> Signed-off-by: Michael Walle <michael@...le.cc>
> ---
>   drivers/nvmem/Kconfig          |  2 ++
>   drivers/nvmem/Makefile         |  1 +
>   drivers/nvmem/core.c           | 57 ++++++++++++++++++++++++++++++++++
>   drivers/nvmem/layouts/Kconfig  |  5 +++
>   drivers/nvmem/layouts/Makefile |  4 +++
>   include/linux/nvmem-provider.h | 38 +++++++++++++++++++++++
>   6 files changed, 107 insertions(+)
>   create mode 100644 drivers/nvmem/layouts/Kconfig
>   create mode 100644 drivers/nvmem/layouts/Makefile

update to ./Documentation/driver-api/nvmem.rst would help others.

> 
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index bab8a29c9861..1416837b107b 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -357,4 +357,6 @@ config NVMEM_U_BOOT_ENV
>   
>   	  If compiled as module it will be called nvmem_u-boot-env.
>   
> +source "drivers/nvmem/layouts/Kconfig"
> +
>   endif
> diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
> index 399f9972d45b..cd5a5baa2f3a 100644
> --- a/drivers/nvmem/Makefile
> +++ b/drivers/nvmem/Makefile
> @@ -5,6 +5,7 @@
>   
>   obj-$(CONFIG_NVMEM)		+= nvmem_core.o
>   nvmem_core-y			:= core.o
> +obj-y				+= layouts/
>   
>   # Devices
>   obj-$(CONFIG_NVMEM_BCM_OCOTP)	+= nvmem-bcm-ocotp.o
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 3dfd149374a8..5357fc378700 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -74,6 +74,9 @@ static LIST_HEAD(nvmem_lookup_list);
>   
>   static BLOCKING_NOTIFIER_HEAD(nvmem_notifier);
>   
> +static DEFINE_SPINLOCK(nvmem_layout_lock);
> +static LIST_HEAD(nvmem_layouts);
> +
>   static int __nvmem_reg_read(struct nvmem_device *nvmem, unsigned int offset,
>   			    void *val, size_t bytes)
>   {
> @@ -744,6 +747,56 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
>   	return 0;
>   }
>   
> +int nvmem_register_layout(struct nvmem_layout *layout)
> +{
> +	spin_lock(&nvmem_layout_lock);
> +	list_add(&layout->node, &nvmem_layouts);
> +	spin_unlock(&nvmem_layout_lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(nvmem_register_layout);

we should provide nvmem_unregister_layout too, so that providers can add 
them if they can in there respective drivers.

> +
> +static struct nvmem_layout *nvmem_get_compatible_layout(struct device_node *np)
> +{
> +	struct nvmem_layout *p, *ret = NULL;
> +
> +	spin_lock(&nvmem_layout_lock);
> +
> +	list_for_each_entry(p, &nvmem_layouts, node) {
> +		if (of_match_node(p->of_match_table, np)) {
> +			ret = p;
> +			break;
> +		}
> +	}
> +
> +	spin_unlock(&nvmem_layout_lock);
> +
> +	return ret;
> +}
> +
> +static int nvmem_add_cells_from_layout(struct nvmem_device *nvmem)
> +{
> +	struct nvmem_layout *layout;
> +
> +	layout = nvmem_get_compatible_layout(nvmem->dev.of_node);
> +	if (layout)
> +		layout->add_cells(&nvmem->dev, nvmem, layout);

access to add_cells can crash hear as we did not check it before adding 
in to list.
Or
we could relax add_cells callback for usecases like imx-octop.


> +
> +	return 0;
> +}
> +
> +const void *nvmem_layout_get_match_data(struct nvmem_device *nvmem,
> +					struct nvmem_layout *layout)
> +{
> +	const struct of_device_id *match;
> +
> +	match = of_match_node(layout->of_match_table, nvmem->dev.of_node);
> +
> +	return match ? match->data : NULL;
> +}
> +EXPORT_SYMBOL_GPL(nvmem_layout_get_match_data);
> +
>   /**
>    * nvmem_register() - Register a nvmem device for given nvmem_config.
>    * Also creates a binary entry in /sys/bus/nvmem/devices/dev-name/nvmem
> @@ -872,6 +925,10 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   	if (rval)
>   		goto err_remove_cells;
>   
> +	rval = nvmem_add_cells_from_layout(nvmem);
> +	if (rval)
> +		goto err_remove_cells;
> +
>   	blocking_notifier_call_chain(&nvmem_notifier, NVMEM_ADD, nvmem);
>   
>   	return nvmem;
> diff --git a/drivers/nvmem/layouts/Kconfig b/drivers/nvmem/layouts/Kconfig
> new file mode 100644
> index 000000000000..9ad3911d1605
> --- /dev/null
> +++ b/drivers/nvmem/layouts/Kconfig
> @@ -0,0 +1,5 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +menu "Layout Types"
> +
> +endmenu
> diff --git a/drivers/nvmem/layouts/Makefile b/drivers/nvmem/layouts/Makefile
> new file mode 100644
> index 000000000000..6fdb3c60a4fa
> --- /dev/null
> +++ b/drivers/nvmem/layouts/Makefile
> @@ -0,0 +1,4 @@
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Makefile for nvmem layouts.
> +#
> diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
> index e710404959e7..323685841e9f 100644
> --- a/include/linux/nvmem-provider.h
> +++ b/include/linux/nvmem-provider.h
> @@ -127,6 +127,28 @@ struct nvmem_cell_table {
>   	struct list_head	node;
>   };
>   
> +/**
> + * struct nvmem_layout - NVMEM layout definitions
> + *
> + * @name:		Layout name.
> + * @of_match_table:	Open firmware match table.
> + * @add_cells:		Will be called if a nvmem device is found which
> + *			has this layout. The function will add layout
> + *			specific cells with nvmem_add_one_cell().
> + * @node:		List node.
> + *
> + * A nvmem device can hold a well defined structure which can just be
> + * evaluated during runtime. For example a TLV list, or a list of "name=val"
> + * pairs. A nvmem layout can parse the nvmem device and add appropriate
> + * cells.
> + */
> +struct nvmem_layout {
> +	const char *name;
> +	const struct of_device_id *of_match_table;

looking at this, I think its doable to convert the existing 
cell_post_process callback to layouts by adding a layout specific 
callback here.


--srini
> +	int (*add_cells)(struct nvmem_device *nvmem, struct nvmem_layout *layout);
> +	struct list_head node;
> +};
> +
>   #if IS_ENABLED(CONFIG_NVMEM)
>   
>   struct nvmem_device *nvmem_register(const struct nvmem_config *cfg);
> @@ -141,6 +163,10 @@ void nvmem_del_cell_table(struct nvmem_cell_table *table);
>   int nvmem_add_one_cell(struct nvmem_device *nvmem,
>   		       const struct nvmem_cell_info *info);
>   
> +int nvmem_register_layout(struct nvmem_layout *layout);
> +const void *nvmem_layout_get_match_data(struct nvmem_device *nvmem,
> +					struct nvmem_layout *layout);
> +
>   #else
>   
>   static inline struct nvmem_device *nvmem_register(const struct nvmem_config *c)
> @@ -161,5 +187,17 @@ static inline void nvmem_del_cell_table(struct nvmem_cell_table *table) {}
>   static inline int nvmem_add_one_cell(struct nvmem_device *nvmem,
>   				     const struct nvmem_cell_info *info) {}
>   
> +static inline int nvmem_register_layout(struct nvmem_layout *layout)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline const void *
> +nvmem_layout_get_match_data(struct nvmem_device *nvmem,
> +			    struct nvmem_layout *layout)
> +{
> +	return NULL;
> +}
> +
>   #endif /* CONFIG_NVMEM */
>   #endif  /* ifndef _LINUX_NVMEM_PROVIDER_H */

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