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Subject: Re: [PATCH v4 1/1] nvmem: Add support for write-only instances
To:     Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>
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 <74d0c4a6-a056-ad45-529e-97b117d4e60b@linaro.org>
 <PSXP216MB0438983CAE5B3086B562BFBA80F70@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM>
From:   Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Message-ID: <f31c6774-198a-32e4-6818-e13d5ff16c85@linaro.org>
Date:   Wed, 18 Mar 2020 09:28:59 +0000
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On 18/03/2020 09:17, Nicholas Johnson wrote:
> 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@outlook.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.
Because you are returning here before device intialize, you would need 
to do the cleanup.

Latest changes are available in linux-next or
https://git.kernel.org/pub/scm/linux/kernel/git/srini/nvmem.git/tree/drivers/nvmem/core.c?h=for-next


Please rebase your patches on top of this branch, so its easy for me to 
apply without conflicts.

--srini
> 
>>
>>> +	}
>>> +
>>>    	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
>>>