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From: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Newsgroups: linux.kernel
Subject: Re: [PATCH 2/6] nvmem: Add backwards compatibility support for older  EEPROM drivers.
Date: Tue, 15 Dec 2015 11:10:02 +0100
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Below are few comments.

On 08/12/15 14:05, Andrew Lunn wrote:
> Older drivers made an 'eeprom' file available in the /sys device
> directory. Have the NVMEM core provide this to retain backwards
> compatibility.
>
> Signed-off-by: Andrew Lunn <andrew@lunn.ch>
> ---
>   drivers/nvmem/Kconfig          |  7 ++++
>   drivers/nvmem/core.c           | 75 +++++++++++++++++++++++++++++++++++++++---
>   include/linux/nvmem-provider.h | 10 ++++++
>   3 files changed, 88 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
> index bc4ea585b42e..b4e79ba7d502 100644
> --- a/drivers/nvmem/Kconfig
> +++ b/drivers/nvmem/Kconfig
> @@ -13,6 +13,13 @@ menuconfig NVMEM
>   	  If unsure, say no.
>
>   if NVMEM
> +config NVMEM_COMPAT
> +       bool "Enable /sys compatibility with old eeprom drivers"
> +       help
> +	 Older EEPROM drivers, such as AT24, AT25, provide access to
> +	 the eeprom via a file called "eeprom" in /sys under the
> +	 device node. Enabling this option makes the NVMEM core
> +	 provide this file to retain backwards compatibility
>
Lets get rid of this Kconfig as Wolfram suggested.
We are already adding NVMEM_COMPAT in the nvmem_device structrure lets 
move the flags into the struct nvmem_config and use the nvmem_register 
api as it is.

nvmem_register() can decide what do do with that from there.
I would also prefer a warning if this flag is set, this is to deter any 
new users.

Let me know your thoughts?

>   config NVMEM_IMX_OCOTP
>   	tristate "i.MX6 On-Chip OTP Controller support"
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 4ccf03da6467..75a498f5e139 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -38,8 +38,13 @@ struct nvmem_device {
>   	int			users;
>   	size_t			size;
>   	bool			read_only;
> +	int			flags;
> +	struct bin_attribute	eeprom;
> +	struct device		*base_dev;
>   };
>
> +#define FLAG_COMPAT		BIT(0)
> +
>   struct nvmem_cell {
>   	const char		*name;
>   	int			offset;
> @@ -62,10 +67,16 @@ static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
>   				    struct bin_attribute *attr,
>   				    char *buf, loff_t pos, size_t count)
>   {
> -	struct device *dev = container_of(kobj, struct device, kobj);
> -	struct nvmem_device *nvmem = to_nvmem_device(dev);
> +	struct device *dev;
> +	struct nvmem_device *nvmem;
>   	int rc;
>
> +	if (attr->private)
> +		dev = attr->private;
> +	else
> +		dev = container_of(kobj, struct device, kobj);
> +	nvmem = to_nvmem_device(dev);
> +
>   	/* Stop the user from reading */
>   	if (pos >= nvmem->size)
>   		return 0;
> @@ -87,10 +98,16 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
>   				     struct bin_attribute *attr,
>   				     char *buf, loff_t pos, size_t count)
>   {
> -	struct device *dev = container_of(kobj, struct device, kobj);
> -	struct nvmem_device *nvmem = to_nvmem_device(dev);
> +	struct device *dev;
> +	struct nvmem_device *nvmem;
>   	int rc;
>
> +	if (attr->private)
> +		dev = attr->private;
> +	else
> +		dev = container_of(kobj, struct device, kobj);
> +	nvmem = to_nvmem_device(dev);
> +
>   	/* Stop the user from writing */
>   	if (pos >= nvmem->size)
>   		return 0;
> @@ -421,6 +438,53 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
>   }
>   EXPORT_SYMBOL_GPL(nvmem_register);
>
> +#if IS_ENABLED(CONFIG_NVMEM_COMPAT)
> +/**
> + * nvmem_register_compat() - Register a nvmem device for given nvmem_config.
> + * Also creates an binary entry in /sys/bus/nvmem/devices/dev-name/nvmem and
> + * an eeprom file in the drivers sys directory.
> + *
> + * @config: nvmem device configuration with which nvmem device is created.
> + * @dev: device structure of underlying device
> + *
> + * Return: Will be an ERR_PTR() on error or a valid pointer to nvmem_device
> + * on success.
> + */
> +
> +struct nvmem_device *nvmem_register_compat(const struct nvmem_config *config,
> +					   struct device *base_dev)
> +{
Possibly move most of it or some of it a local static function which 
will be called from nvmem_register depending on the NVMEM_FLAG_COMPAT.

> +	struct nvmem_device *nvmem;
> +	int rval;
> +
> +	nvmem = nvmem_register(config);
> +	if (IS_ERR(nvmem))
> +		return nvmem;
> +
> +	if (nvmem->read_only)
> +		nvmem->eeprom = bin_attr_ro_root_nvmem;
> +	else
> +		nvmem->eeprom = bin_attr_rw_root_nvmem;
> +	nvmem->eeprom.attr.name = "eeprom";
> +	nvmem->eeprom.size = nvmem->size;
> +	nvmem->eeprom.private = &nvmem->dev;
> +	nvmem->base_dev = base_dev;
> +
> +	rval = device_create_bin_file(nvmem->base_dev, &nvmem->eeprom);
> +	if (rval) {
> +		dev_err(&nvmem->dev,
> +			"Failed to create eeprom binary file %d\n", rval);
> +		nvmem_unregister(nvmem);
> +		return ERR_PTR(rval);
> +	}
> +
> +	nvmem->flags |= FLAG_COMPAT;
> +
> +	return nvmem;
> +}
> +EXPORT_SYMBOL_GPL(nvmem_register_compat);
> +#endif /* CONFIG_NVMEM_COMPAT */
> +
>   /**
>    * nvmem_unregister() - Unregister previously registered nvmem device
>    *
> @@ -437,6 +501,9 @@ int nvmem_unregister(struct nvmem_device *nvmem)
>   	}
>   	mutex_unlock(&nvmem_mutex);
>
> +	if (nvmem->flags & FLAG_COMPAT)
> +		device_remove_bin_file(nvmem->base_dev, &nvmem->eeprom);
> +
>   	nvmem_device_remove_all_cells(nvmem);
>   	device_del(&nvmem->dev);
>
> diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
> index d24fefa0c11d..012030bd4495 100644
> --- a/include/linux/nvmem-provider.h
> +++ b/include/linux/nvmem-provider.h
> @@ -45,4 +45,14 @@ static inline int nvmem_unregister(struct nvmem_device *nvmem)
>
>   #endif /* CONFIG_NVMEM */
>
> +#if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_NVMEM_COMPAT)
> +struct nvmem_device *nvmem_register_compat(const struct nvmem_config *config,
> +					   struct device *base_dev);
> +#else
> +static inline struct nvmem_device *
> +nvmem_register_compat(const struct nvmem_config *c, struct device *base_dev)
> +{
> +	return ERR_PTR(-ENOSYS);
> +}
> +#endif  /* CONFIG_NVMEM && CONFIG_NVMEM_COMPAT */
>   #endif  /* ifndef _LINUX_NVMEM_PROVIDER_H */
>
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