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    SubjectRe: [PATCH v2 02/25] mtd: add support for reading MTD devices via the nvmem API
    On Tue, 13 Nov 2018 15:01:10 +0100
    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.
    >
    > We don't support device tree systems for now.
    >
    > Signed-off-by: Alban Bedel <albeu@free.fr>
    > [Bartosz:
    > - include linux/nvmem-provider.h
    > - set the name of the nvmem provider
    > - set no_of_node to true in nvmem_config
    > - don't check the return value of nvmem_unregister() - it cannot fail
    > - tweaked the commit message]
    > Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

    Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>

    To the person taking this patch (Greg?): I'll need an immutable tag,
    just in case we end up with other changes in mtdcore.c for this release.

    > ---
    > drivers/mtd/Kconfig | 1 +
    > drivers/mtd/mtdcore.c | 56 +++++++++++++++++++++++++++++++++++++++++
    > include/linux/mtd/mtd.h | 2 ++
    > 3 files changed, 59 insertions(+)
    >
    > diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
    > index c77f537323ec..efbe7a6f1d8f 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 97ac219c082e..5f1053d995b0 100644
    > --- a/drivers/mtd/mtdcore.c
    > +++ b/drivers/mtd/mtdcore.c
    > @@ -41,6 +41,7 @@
    > #include <linux/reboot.h>
    > #include <linux/leds.h>
    > #include <linux/debugfs.h>
    > +#include <linux/nvmem-provider.h>
    >
    > #include <linux/mtd/mtd.h>
    > #include <linux/mtd/partitions.h>
    > @@ -488,6 +489,50 @@ 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.name = mtd->name;
    > + 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.root_only = true;
    > + config.no_of_node = true;
    > + config.priv = mtd;
    > +
    > + mtd->nvmem = nvmem_register(&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 +615,11 @@ 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 +645,8 @@ 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);
    > @@ -637,6 +689,10 @@ int del_mtd_device(struct mtd_info *mtd)
    > mtd->index, mtd->name, mtd->usecount);
    > ret = -EBUSY;
    > } else {
    > + /* Try to remove the NVMEM provider */
    > + if (mtd->nvmem)
    > + nvmem_unregister(mtd->nvmem);
    > +
    > device_unregister(&mtd->dev);
    >
    > idr_remove(&mtd_idr, mtd->index);
    > diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
    > index cd0be91bdefa..545070c2ee64 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>
    >
    > @@ -341,6 +342,7 @@ 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,

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