[PATCH v1 0/4] Introduce mtdblock device

[Frieder Schrempf]

Hi Alexey,

On 01.03.24 14:42, Alexey Romanov wrote:
> Hi Frieder,
> 
> On Thu, Feb 29, 2024 at 09:51:04AM +0100, Frieder Schrempf wrote:
>> Hi Alexey,
>>
>> On 27.02.24 11:04, Alexey Romanov wrote:
>>> Hello!
>>>
>>> This series adds support for the mtdblock device, which
>>> allows to read/write data block by block. For example,
>>> it can now be used for BCB or Android AB command:
>>>
>>>   $ bcb load mtd 0 part_name
>>>
>>> Tested only on SPI NAND, so bind is made only for
>>> SPI NAND drivers.
>>
>> I don't know much about Android, but as far as I understand you are
>> trying to store dynamic, boot-related information on the MTD device.
>>
>> This might be acceptable if the underlying device is a NOR flash, but
>> for any type of NAND device it sounds like a rather bad idea.
>>
>> NAND devices need some kind of FTL (flash translation layer) in order to
>> work reliably. Using a block filesystem directly on the NAND MTD device
>> will cause problems as soon as any bad blocks or bit flips occur.
>>
>> People are therefore discouraged to use mtdblock on NAND and in the
>> kernel there is even a warning if you try to mount a NAND mtdblock
>> partition.
> 
> You are completely right. But, unfortunately, these are legacy ones that
> need to be supported. On some boards this approach was chosen a long
> time ago and mistakenly, so I think we need to support this for NAND.
> 
>>
>> Maybe you should reconsider this and look into how to use UBIFS as a
>> FTL. On the other hand I'm not quite sure if the UBIFS layer in U-Boot
>> is really stable and maintained. So this might not be a good idea either.
> 
> Yeah, on our new boards we switched to using UBI, and we already have 
> an implementation UBI block device for U-Boot. Will send this to
> mailing list in the near future.
> 
>>
>> Anyway, I'm against implementing mtdblock for SPI NAND (or any other NAND).
> 
> Maybe we'll just add warning like it's done in the Linux?

If we really need this, then yes, please add a warning that is printed
to the console.

Thanks
Frieder