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Date:   Fri, 17 Aug 2018 18:27:20 +0200
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Bartosz Golaszewski <brgl@bgdev.pl>
Cc:     Jonathan Corbet <corbet@lwn.net>, Sekhar Nori <nsekhar@ti.com>,
        Kevin Hilman <khilman@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Grygorii Strashko <grygorii.strashko@ti.com>,
        "David S . Miller" <davem@davemloft.net>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Naren <naren.kernel@gmail.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Lukas Wunner <lukas@wunner.de>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>,
        Sven Van Asbroeck <svendev@arcx.com>,
        Paolo Abeni <pabeni@redhat.com>, Alban Bedel <albeu@free.fr>,
        Rob Herring <robh@kernel.org>,
        David Lechner <david@lechnology.com>,
        Andrew Lunn <andrew@lunn.ch>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-i2c@vger.kernel.org, linux-mtd@lists.infradead.org,
        linux-omap@vger.kernel.org, netdev@vger.kernel.org,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>
Subject: Re: [PATCH v2 06/29] mtd: Add support for reading MTD devices via
 the nvmem API
Message-ID: <20180817182720.6a6e5e8e@bbrezillon>
In-Reply-To: <20180810080526.27207-7-brgl@bgdev.pl>
References: <20180810080526.27207-1-brgl@bgdev.pl>
        <20180810080526.27207-7-brgl@bgdev.pl>
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Hi Bartosz,

On Fri, 10 Aug 2018 10:05:03 +0200
Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Alban Bedel <albeu@free.fr>
> 
> Allow drivers that use the nvmem API to read data stored on MTD devices.
> For this the mtd devices are registered as read-only NVMEM providers.
> 
> Signed-off-by: Alban Bedel <albeu@free.fr>
> [Bartosz:
>   - use the managed variant of nvmem_register(),
>   - set the nvmem name]
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

What happened to the 2 other patches of Alban's series? I'd really like
the DT case to be handled/agreed on in the same patchset, but IIRC,
Alban and Srinivas disagreed on how this should be represented. I
hope this time we'll come to an agreement, because the MTD <-> NVMEM
glue has been floating around for quite some time...

Regards,

Boris

> ---
>  drivers/mtd/Kconfig     |  1 +
>  drivers/mtd/mtdcore.c   | 50 +++++++++++++++++++++++++++++++++++++++++
>  include/linux/mtd/mtd.h |  2 ++
>  3 files changed, 53 insertions(+)
> 
> diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
> index 46ab7feec6b6..f5549482d0df 100644
> --- a/drivers/mtd/Kconfig
> +++ b/drivers/mtd/Kconfig
> @@ -1,5 +1,6 @@
>  menuconfig MTD
>  	tristate "Memory Technology Device (MTD) support"
> +	imply NVMEM
>  	help
>  	  Memory Technology Devices are flash, RAM and similar chips, often
>  	  used for solid state file systems on embedded devices. This option
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 42395df06be9..a57302eaceb5 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -488,6 +488,49 @@ int mtd_pairing_groups(struct mtd_info *mtd)
>  }
>  EXPORT_SYMBOL_GPL(mtd_pairing_groups);
>  
> +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;
> +}
> +
> +static int mtd_nvmem_add(struct mtd_info *mtd)
> +{
> +	struct nvmem_config config = { };
> +
> +	config.dev = &mtd->dev;
> +	config.owner = THIS_MODULE;
> +	config.name = mtd->name;
> +	config.reg_read = mtd_nvmem_reg_read;
> +	config.size = mtd->size;
> +	config.word_size = 1;
> +	config.stride = 1;
> +	config.read_only = true;
> +	config.root_only = true;
> +	config.priv = mtd;
> +
> +	mtd->nvmem = devm_nvmem_register(&mtd->dev, &config);
> +	if (IS_ERR(mtd->nvmem)) {
> +		/* Just ignore if there is no NVMEM support in the kernel */
> +		if (PTR_ERR(mtd->nvmem) == -ENOSYS) {
> +			mtd->nvmem = NULL;
> +		} else {
> +			dev_err(&mtd->dev, "Failed to register NVMEM device\n");
> +			return PTR_ERR(mtd->nvmem);
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  static struct dentry *dfs_dir_mtd;
>  
>  /**
> @@ -570,6 +613,11 @@ 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;
> +
>  	if (!IS_ERR_OR_NULL(dfs_dir_mtd)) {
>  		mtd->dbg.dfs_dir = debugfs_create_dir(dev_name(&mtd->dev), dfs_dir_mtd);
>  		if (IS_ERR_OR_NULL(mtd->dbg.dfs_dir)) {
> @@ -595,6 +643,8 @@ 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);
> diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
> index a86c4fa93115..8121c6582285 100644
> --- a/include/linux/mtd/mtd.h
> +++ b/include/linux/mtd/mtd.h
> @@ -25,6 +25,7 @@
>  #include <linux/notifier.h>
>  #include <linux/device.h>
>  #include <linux/of.h>
> +#include <linux/nvmem-provider.h>
>  
>  #include <mtd/mtd-abi.h>
>  
> @@ -339,6 +340,7 @@ struct mtd_info {
>  	struct device dev;
>  	int usecount;
>  	struct mtd_debug_info dbg;
> +	struct nvmem_device *nvmem;
>  };
>  
>  int mtd_ooblayout_ecc(struct mtd_info *mtd, int section,