Date:   Wed, 18 Mar 2020 09:17:48 +0000
From:   Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v4 1/1] nvmem: Add support for write-only instances

On Tue, Mar 17, 2020 at 02:35:44PM +0000, Srinivas Kandagatla wrote:
> 
> 
> On 17/03/2020 01:01, Nicholas Johnson wrote:
> > There is at least one real-world use-case for write-only nvmem
> > instances. Refer to 03cd45d2e219 ("thunderbolt: Prevent crash if
> > non-active NVMem file is read").
> > 
> > Add support for write-only nvmem instances by adding attrs for 0200.
> > 
> > Change nvmem_register() to abort if NULL group is returned from
> > nvmem_sysfs_get_groups().
> > 
> > Return NULL from nvmem_sysfs_get_groups() in invalid cases.
> > 
> > Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> > ---
> >   drivers/nvmem/core.c        |  9 ++++--
> >   drivers/nvmem/nvmem-sysfs.c | 56 +++++++++++++++++++++++++++++++------
> >   2 files changed, 54 insertions(+), 11 deletions(-)
> > 
> > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> > index ef326f243..95ea9a3b2 100644
> > --- a/drivers/nvmem/core.c
> > +++ b/drivers/nvmem/core.c
> > @@ -373,6 +373,12 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >   	nvmem->type = config->type;
> >   	nvmem->reg_read = config->reg_read;
> >   	nvmem->reg_write = config->reg_write;
> > +	nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);
> > +	if (!nvmem->dev.groups) {
> > +		kfree(nvmem);
> > +		return ERR_PTR(-EINVAL);
> 
> When I meant leaking here, not just memory but other resources like idr and
> gpio.
> 
> You should do something like this:
> 
> if (!nvmem->dev.groups) {
> 	ida_simple_remove(&nvmem_ida, nvmem->id);
> 	gpiod_put(nvmem->wp_gpio);
> 	kfree(nvmem);
> 	return ERR_PTR(-EINVAL);
> }
Thanks. I am guessing these are called indirectly when there are other 
failures (goto err_*). We have ida_simple_remove() in nvmem_release() 
but I cannot find gpiod_put anywhere in drivers/nvmem.

> 
> > +	}
> > +
> >   	if (!config->no_of_node)
> >   		nvmem->dev.of_node = config->dev->of_node;
> > @@ -387,8 +393,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >   	nvmem->read_only = device_property_present(config->dev, "read-only") ||
> >   			   config->read_only || !nvmem->reg_write;
> > -	nvmem->dev.groups = nvmem_sysfs_get_groups(nvmem, config);
> > -
> >   	device_initialize(&nvmem->dev);
> >   	dev_dbg(&nvmem->dev, "Registering nvmem device %s\n", config->name);
> > @@ -430,7 +434,6 @@ struct nvmem_device *nvmem_register(const struct nvmem_config *config)
> >   	device_del(&nvmem->dev);
> >   err_put_device:
> >   	put_device(&nvmem->dev);
> > -
> unnecessary cleanup here!
Sorry, I let this mistake slip, despite checking my work.

> 
> Other than that every thing looks good to me!
> 
> 
> --srini

Cheers,
Nicholas
> 
> >   	return ERR_PTR(rval);
> >   }
> >   EXPORT_SYMBOL_GPL(nvmem_register);
> > diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c
> > index 9e0c429cd..4ceac8680 100644
> > --- a/drivers/nvmem/nvmem-sysfs.c
> > +++ b/drivers/nvmem/nvmem-sysfs.c
> > @@ -196,16 +196,49 @@ static const struct attribute_group *nvmem_ro_root_dev_groups[] = {
> >   	NULL,
> >   };
> > +/* write only permission, root only */
> > +static struct bin_attribute bin_attr_wo_root_nvmem = {
> > +	.attr	= {
> > +		.name	= "nvmem",
> > +		.mode	= 0200,
> > +	},
> > +	.write	= bin_attr_nvmem_write,
> > +};
> > +
> > +static struct bin_attribute *nvmem_bin_wo_root_attributes[] = {
> > +	&bin_attr_wo_root_nvmem,
> > +	NULL,
> > +};
> > +
> > +static const struct attribute_group nvmem_bin_wo_root_group = {
> > +	.bin_attrs	= nvmem_bin_wo_root_attributes,
> > +	.attrs		= nvmem_attrs,
> > +};
> > +
> > +static const struct attribute_group *nvmem_wo_root_dev_groups[] = {
> > +	&nvmem_bin_wo_root_group,
> > +	NULL,
> > +};
> > +
> >   const struct attribute_group **nvmem_sysfs_get_groups(
> >   					struct nvmem_device *nvmem,
> >   					const struct nvmem_config *config)
> >   {
> > -	if (config->root_only)
> > -		return nvmem->read_only ?
> > -			nvmem_ro_root_dev_groups :
> > -			nvmem_rw_root_dev_groups;
> > +	/* Read-only */
> > +	if (nvmem->reg_read && (!nvmem->reg_write || nvmem->read_only))
> > +		return config->root_only ?
> > +			nvmem_ro_root_dev_groups : nvmem_ro_dev_groups;
> > +
> > +	/* Read-write */
> > +	if (nvmem->reg_read && nvmem->reg_write && !nvmem->read_only)
> > +		return config->root_only ?
> > +			nvmem_rw_root_dev_groups : nvmem_rw_dev_groups;
> > +
> > +	/* Write-only, do not honour request for global writable entry */
> > +	if (!nvmem->reg_read && nvmem->reg_write && !nvmem->read_only)
> > +		return config->root_only ? nvmem_wo_root_dev_groups : NULL;
> > -	return nvmem->read_only ? nvmem_ro_dev_groups : nvmem_rw_dev_groups;
> > +	return NULL;
> >   }
> >   /*
> > @@ -224,17 +257,24 @@ int nvmem_sysfs_setup_compat(struct nvmem_device *nvmem,
> >   	if (!config->base_dev)
> >   		return -EINVAL;
> > -	if (nvmem->read_only) {
> > +	if (nvmem->reg_read && (!nvmem->reg_write || nvmem->read_only)) {
> >   		if (config->root_only)
> >   			nvmem->eeprom = bin_attr_ro_root_nvmem;
> >   		else
> >   			nvmem->eeprom = bin_attr_ro_nvmem;
> > -	} else {
> > +	} else if (!nvmem->reg_read && nvmem->reg_write && !nvmem->read_only) {
> > +		if (config->root_only)
> > +			nvmem->eeprom = bin_attr_wo_root_nvmem;
> > +		else
> > +			return -EINVAL;
> > +	} else if (nvmem->reg_read && nvmem->reg_write && !nvmem->read_only) {
> >   		if (config->root_only)
> >   			nvmem->eeprom = bin_attr_rw_root_nvmem;
> >   		else
> >   			nvmem->eeprom = bin_attr_rw_nvmem;
> > -	}
> > +	} else
> > +		return -EINVAL;
> > +
> >   	nvmem->eeprom.attr.name = "eeprom";
> >   	nvmem->eeprom.size = nvmem->size;
> >   #ifdef CONFIG_DEBUG_LOCK_ALLOC
> > 

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