Re: [PATCH 4/4] nvmem: layouts: add U-Boot env layout

["Rafał Miłecki" <zajec5@gmail.com>]

On 19.12.2023 08:55, Miquel Raynal wrote:
> Hi Rafał,
> 
> zajec5@gmail.com wrote on Mon, 18 Dec 2023 23:10:20 +0100:
> 
>> On 18.12.2023 15:21, Miquel Raynal wrote:
>>> Hi Rafał,
>>>
>>> zajec5@gmail.com wrote on Mon, 18 Dec 2023 14:37:22 +0100:
>>>    
>>>> From: Rafał Miłecki <rafal@milecki.pl>
>>>>
>>>> This patch moves all generic (NVMEM devices independent) code from NVMEM
>>>> device driver to NVMEM layout driver. Then it adds a simple NVMEM layout
>>>> code on top of it.
>>>>
>>>> Thanks to proper layout it's possible to support U-Boot env data stored
>>>> on any kind of NVMEM device.
>>>>
>>>> For backward compatibility with old DT bindings we need to keep old
>>>> NVMEM device driver functional. To avoid code duplication a parsing
>>>> function is exported and reused in it.
>>>>
>>>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>>>> ---
>>>
>>> I have a couple of comments about the original driver which gets
>>> copy-pasted in the new layout driver, maybe you could clean these
>>> (the memory leak should be fixed before the migration so it can be
>>> backported easily, the others are just style so it can be done after, I
>>> don't mind).
>>>
>>> ...
>>>    
>>>> +int u_boot_env_parse(struct device *dev, struct nvmem_device *nvmem,
>>>> +		     enum u_boot_env_format format)
>>>> +{
>>>> +	size_t crc32_data_offset;
>>>> +	size_t crc32_data_len;
>>>> +	size_t crc32_offset;
>>>> +	size_t data_offset;
>>>> +	size_t data_len;
>>>> +	size_t dev_size;
>>>> +	uint32_t crc32;
>>>> +	uint32_t calc;
>>>> +	uint8_t *buf;
>>>> +	int bytes;
>>>> +	int err;
>>>> +
>>>> +	dev_size = nvmem_dev_size(nvmem);
>>>> +
>>>> +	buf = kcalloc(1, dev_size, GFP_KERNEL);
>>>
>>> Out of curiosity, why kcalloc(1,...) rather than kzalloc() ?
>>
>> I used kcalloc() initially as I didn't need buffer to be zeroed.
> 
> I think kcalloc() initializes the memory to zero.
> https://elixir.bootlin.com/linux/latest/source/include/linux/slab.h#L659
> 
> If you don't need it you can switch to kmalloc() instead, I don't mind,
> but kcalloc() is meant to be used with arrays, I don't see the point of
> using kcalloc() in this case.
> 
>>
>> I see that memory-allocation.rst however says:
>>   > And, to be on the safe side it's best to use routines that set memory to zero, like kzalloc().
>>
>> It's probably close to zero cost to zero that buffer so it could be kzalloc().
>>
>>
>>>> +	if (!buf) {
>>>> +		err = -ENOMEM;
>>>> +		goto err_out;
>>>
>>> We could directly return ENOMEM here I guess.
>>>    
>>>> +	}
>>>> +
>>>> +	bytes = nvmem_device_read(nvmem, 0, dev_size, buf);
>>>> +	if (bytes < 0)
>>>> +		return bytes;
>>>> +	else if (bytes != dev_size)
>>>> +		return -EIO;
>>>
>>> Don't we need to free buf in the above cases?
>>>    
>>>> +	switch (format) {
>>>> +	case U_BOOT_FORMAT_SINGLE:
>>>> +		crc32_offset = offsetof(struct u_boot_env_image_single, crc32);
>>>> +		crc32_data_offset = offsetof(struct u_boot_env_image_single, data);
>>>> +		data_offset = offsetof(struct u_boot_env_image_single, data);
>>>> +		break;
>>>> +	case U_BOOT_FORMAT_REDUNDANT:
>>>> +		crc32_offset = offsetof(struct u_boot_env_image_redundant, crc32);
>>>> +		crc32_data_offset = offsetof(struct u_boot_env_image_redundant, data);
>>>> +		data_offset = offsetof(struct u_boot_env_image_redundant, data);
>>>> +		break;
>>>> +	case U_BOOT_FORMAT_BROADCOM:
>>>> +		crc32_offset = offsetof(struct u_boot_env_image_broadcom, crc32);
>>>> +		crc32_data_offset = offsetof(struct u_boot_env_image_broadcom, data);
>>>> +		data_offset = offsetof(struct u_boot_env_image_broadcom, data);
>>>> +		break;
>>>> +	}
>>>> +	crc32 = le32_to_cpu(*(__le32 *)(buf + crc32_offset));
>>>
>>> Looks a bit convoluted, any chances we can use intermediate variables
>>> to help decipher this?
>>>    
>>>> +	crc32_data_len = dev_size - crc32_data_offset;
>>>> +	data_len = dev_size - data_offset;
>>>> +
>>>> +	calc = crc32(~0, buf + crc32_data_offset, crc32_data_len) ^ ~0L;
>>>> +	if (calc != crc32) {
>>>> +		dev_err(dev, "Invalid calculated CRC32: 0x%08x (expected: 0x%08x)\n", calc, crc32);
>>>> +		err = -EINVAL;
>>>> +		goto err_kfree;
>>>> +	}
>>>> +
>>>> +	buf[dev_size - 1] = '\0';
>>>> +	err = u_boot_env_parse_cells(dev, nvmem, buf, data_offset, data_len);
>>>> +	if (err)
>>>> +		dev_err(dev, "Failed to add cells: %d\n", err);
>>>
>>> Please drop this error message, the only reason for which the function
>>> call would fail is apparently an ENOMEM case.
>>>    
>>>> +
>>>> +err_kfree:
>>>> +	kfree(buf);
>>>> +err_out:
>>>> +	return err;
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(u_boot_env_parse);
>>>> +
>>>> +static int u_boot_env_add_cells(struct device *dev, struct nvmem_device *nvmem)
>>>> +{
>>>> +	const struct of_device_id *match;
>>>> +	struct device_node *layout_np;
>>>> +	enum u_boot_env_format format;
>>>> +
>>>> +	layout_np = of_nvmem_layout_get_container(nvmem);
>>>> +	if (!layout_np)
>>>> +		return -ENOENT;
>>>> +
>>>> +	match = of_match_node(u_boot_env_of_match_table, layout_np);
>>>> +	if (!match)
>>>> +		return -ENOENT;
>>>> +
>>>> +	format = (uintptr_t)match->data;
>>>
>>> In the core there is currently an unused helper called
>>> nvmem_layout_get_match_data() which does that. I think the original
>>> intent of this function was to be used in this driver, so depending on
>>> your preference, can you please either use it or remove it?
>>
>> The problem is that nvmem_layout_get_match_data() uses:
>> layout->dev.driver
> 
> I'm surprised .driver is unset. Well anyway, please either fix the core
> helper and use it or drop the core helper, because we have no user for
> it otherwise?

I believe it's because of a very minimalistic "nvmem_bus_type" bus
implementation.

 From a quick look it seems that default expected FORWARD-trace is:
driver_register()
bus_add_driver()
driver_attach()
__driver_attach()
driver_probe_device()
__driver_probe_device()
really_probe()

It's really_probe() that seems to set dev->driver pointer.


>> It doesn't work with layouts driver (since refactoring?) as driver is
>> NULL. That results in NULL pointer dereference when trying to reach
>> of_match_table.
>>
>> That is why I used u_boot_env_of_match_table directly.
>>
>> If you know how to fix nvmem_layout_get_match_data() that would be
>> great. Do we need driver_register() somewhere in NVMEM core?