Re: [PATCH v2 2/2] mtd: Add support for reading MTD devices via the nvmem API

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Tue,  7 Mar 2017 09:26:04 +0100
Alban <albeu@free.fr> wrote:

> Allow drivers that use the nvmem API to read data stored on MTD devices.
> Add an option to the MTD core that allow registering the MTD as
> read-only NVMEM providers.
> 
> Signed-off-by: Alban <albeu@free.fr>
> ---
> Changelog:
> v2: * Moved to the MTD core instead of using notifiers
>     * Fixed the Kconfig description
> ---
>  drivers/mtd/Kconfig     |  9 +++++++
>  drivers/mtd/Makefile    |  1 +
>  drivers/mtd/mtdcore.c   | 13 +++++++++
>  drivers/mtd/mtdnvmem.c  | 72 +++++++++++++++++++++++++++++++++++++++++++++++++
>  drivers/mtd/mtdnvmem.h  | 25 +++++++++++++++++
>  include/linux/mtd/mtd.h |  4 +++
>  6 files changed, 124 insertions(+)
>  create mode 100644 drivers/mtd/mtdnvmem.c
>  create mode 100644 drivers/mtd/mtdnvmem.h
> 
> diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
> index e83a279..5a34c6a 100644
> --- a/drivers/mtd/Kconfig
> +++ b/drivers/mtd/Kconfig
> @@ -322,6 +322,15 @@ config MTD_PARTITIONED_MASTER
>  	  the parent of the partition device be the master device, rather than
>  	  what lies behind the master.
>  
> +config MTD_NVMEM
> +	bool "Register MTD devices as NVMEM providers"
> +	default y
> +	depends on NVMEM || COMPILE_TEST
> +	help
> +	  Provides support for reading config data from MTD devices. This can
> +	  be used by drivers to read device specific data such as MAC addresses
> +	  or calibration results.
> +
>  source "drivers/mtd/chips/Kconfig"
>  
>  source "drivers/mtd/maps/Kconfig"
> diff --git a/drivers/mtd/Makefile b/drivers/mtd/Makefile
> index 99bb9a1..879a542 100644
> --- a/drivers/mtd/Makefile
> +++ b/drivers/mtd/Makefile
> @@ -5,6 +5,7 @@
>  # Core functionality.
>  obj-$(CONFIG_MTD)		+= mtd.o
>  mtd-y				:= mtdcore.o mtdsuper.o mtdconcat.o mtdpart.o mtdchar.o
> +mtd-$(CONFIG_MTD_NVMEM)		+= mtdnvmem.o
>  
>  obj-$(CONFIG_MTD_OF_PARTS)	+= ofpart.o
>  obj-$(CONFIG_MTD_REDBOOT_PARTS) += redboot.o
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 66a9ded..bb88997 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -45,6 +45,7 @@
>  #include <linux/mtd/partitions.h>
>  
>  #include "mtdcore.h"
> +#include "mtdnvmem.h"
>  
>  static struct backing_dev_info *mtd_bdi;
>  
> @@ -554,6 +555,11 @@ int add_mtd_device(struct mtd_info *mtd)
>  	if (error)
>  		goto fail_added;
>  
> +	/* Add the nvmem provider */
> +	error = mtd_nvmem_add(mtd);
> +	if (error)
> +		goto fail_nvmem_add;
> +
>  	device_create(&mtd_class, mtd->dev.parent, MTD_DEVT(i) + 1, NULL,
>  		      "mtd%dro", i);
>  
> @@ -571,6 +577,8 @@ int add_mtd_device(struct mtd_info *mtd)
>  	__module_get(THIS_MODULE);
>  	return 0;
>  
> +fail_nvmem_add:
> +	device_unregister(&mtd->dev);
>  fail_added:
>  	of_node_put(mtd_get_of_node(mtd));
>  	idr_remove(&mtd_idr, i);
> @@ -611,6 +619,11 @@ int del_mtd_device(struct mtd_info *mtd)
>  		       mtd->index, mtd->name, mtd->usecount);
>  		ret = -EBUSY;
>  	} else {
> +		/* Try to remove the NVMEM provider */
> +		ret = mtd_nvmem_remove(mtd);
> +		if (ret)
> +			goto out_error;
> +
>  		device_unregister(&mtd->dev);
>  
>  		idr_remove(&mtd_idr, mtd->index);
> diff --git a/drivers/mtd/mtdnvmem.c b/drivers/mtd/mtdnvmem.c
> new file mode 100644
> index 0000000..d6bc402
> --- /dev/null
> +++ b/drivers/mtd/mtdnvmem.c
> @@ -0,0 +1,72 @@
> +/*
> + * Copyright (C) 2017 Alban Bedel <albeu@free.fr>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/mtd/mtd.h>
> +#include <linux/nvmem-provider.h>
> +#include <linux/of.h>
> +
> +static int mtd_nvmem_reg_read(void *priv, unsigned int offset,
> +			      void *val, size_t bytes)
> +{
> +	struct mtd_info *mtd = priv;
> +	size_t retlen;
> +	int err;
> +
> +	err = mtd_read(mtd, offset, bytes, &retlen, val);
> +	if (err && err != -EUCLEAN)
> +		return err;
> +
> +	return retlen == bytes ? 0 : -EIO;
> +}
> +
> +int mtd_nvmem_add(struct mtd_info *mtd)
> +{
> +	struct device_node *np = dev_of_node(&mtd->dev);
> +	struct nvmem_config config = {};
> +
> +	/* OF devices must have the nvmem-provider property */
> +	if (np && !of_property_read_bool(np, "nvmem-provider"))
> +		return 0;
> +
> +	config.dev = &mtd->dev;
> +	config.owner = THIS_MODULE;
> +	config.reg_read = mtd_nvmem_reg_read;
> +	config.size = mtd->size;
> +	config.word_size = 1;
> +	config.stride = 1;
> +	config.read_only = true;
> +	config.priv = mtd;
> +
> +	mtd->nvmem = nvmem_register(&config);
> +	if (IS_ERR(mtd->nvmem)) {
> +		dev_err(&mtd->dev, "Failed to register NVMEM device\n");
> +		return PTR_ERR(mtd->nvmem);
> +	}
> +
> +	return 0;
> +}
> +
> +int mtd_nvmem_remove(struct mtd_info *mtd)
> +{
> +	int ret;
> +
> +	if (!mtd->nvmem)
> +		return 0;
> +
> +	ret = nvmem_unregister(mtd->nvmem);
> +	if (ret)
> +		dev_err(&mtd->dev, "Failed to unregister NVMEM device\n");
> +
> +	return ret;
> +}

Given the amount of code I wonder if this shouldn't be integrated in
mtdcore.c and unconditionally compiled in.

> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Alban Bedel <albeu@free.fr>");
> +MODULE_DESCRIPTION("Driver to read config data from MTD devices");
> diff --git a/drivers/mtd/mtdnvmem.h b/drivers/mtd/mtdnvmem.h
> new file mode 100644
> index 0000000..a49d8bd
> --- /dev/null
> +++ b/drivers/mtd/mtdnvmem.h
> @@ -0,0 +1,25 @@
> +/*
> + * Copyright (C) 2017 Alban Bedel <albeu@free.fr>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +#ifndef MTD_NVMEM_H
> +#define MTD_NVMEM_H 1
> +
> +struct mtd_info;
> +
> +#ifdef CONFIG_MTD_NVMEM
> +int mtd_nvmem_add(struct mtd_info *mtd);
> +int mtd_nvmem_remove(struct mtd_info *mtd);
> +#else
> +static inline int mtd_nvmem_add(struct mtd_info *mtd)
> +{ return 0; }
> +
> +static inline int mtd_nvmem_remove(struct mtd_info *mtd)
> +{ return 0; }
> +#endif
> +
> +#endif /* MTD_NVMEM_H */
> diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
> index eebdc63..e06c6e6 100644
> --- a/include/linux/mtd/mtd.h
> +++ b/include/linux/mtd/mtd.h
> @@ -205,6 +205,7 @@ struct mtd_pairing_scheme {
>  };
>  
>  struct module;	/* only needed for owner field in mtd_info */
> +struct nvmem_device;

Include nvmem-provider.h instead of re-defining struct nvmem_device
here.

>  
>  struct mtd_info {
>  	u_char type;
> @@ -351,6 +352,9 @@ struct mtd_info {
>  	struct module *owner;
>  	struct device dev;
>  	int usecount;
> +#if IS_ENABLED(CONFIG_MTD_NVMEM)
> +	struct nvmem_device *nvmem;
> +#endif

Hm, I don't see any #if IS_ENABLED() or #ifdef CONFIG_ statements in
this file. I know it adds an extra 32/64 bits field for nothing if the
feature is disabled, but how about keeping the struct definition simple
by unconditionally adding the nvmem field. 

>  };
>  
>  int mtd_ooblayout_ecc(struct mtd_info *mtd, int section,