fs: littlefs: Fix cache and lookahead size checks in littlefs_fs for block devices

[DNedic]

This fixes an issue where wrong values were checked against block device defaults. Kconfig values are used when no filesystem config values are provided, and the buffers are sized according to the Kconfig values, but the checks were only performed against filesystem instance specific config variables.

[DNedic]

I'm interested in why cache and lookahead buffer values are being reduced, especially when buffers have been already assigned.

[de-nordic]

I'm interested in why cache and lookahead buffer values are being reduced, especially when buffers have been already assigned.

To align with block size of a device: 09574e6

[de-nordic]

This fixes an issue where wrong values were checked against block device defaults. Kconfig values are used when no filesystem config values are provided, and the buffers are sized according to the Kconfig values, but the checks were only performed against filesystem config variables.

The default are only used when not instance specific not provided.

[DNedic]

I'm interested in why cache and lookahead buffer values are being reduced, especially when buffers have been already assigned.

To align with block size of a device: 09574e6

In that case wouldn't it make more sense to round down to the closest smaller multiple of block size? With a cache size set to 2047, it will still be reduced to 512 despite 1536 being smaller than 2047 and a multiple of 512.

[DNedic]

This fixes an issue where wrong values were checked against block device defaults. Kconfig values are used when no filesystem config values are provided, and the buffers are sized according to the Kconfig values, but the checks were only performed against filesystem config variables.

The default are only used when not instance specific not provided.

Exactly, however in this case we are only checking against instance specific, which is 0 when nothing is provided.

[de-nordic]

The default are only used when not instance specific not provided.

Exactly, however in this case we are only checking against instance specific, which is 0 when nothing is provided.

Ah, right. There is a bug because the cache_size serves as test variable that is set between lines 780-784 to either instance specific or default, so the comparison in these lines was not actually testing the right variable in the end.

[DNedic]

I'm also going to submit a new PR to change the block alignment behavior for these values, but it might be better to merge this as a quick fix since it breaks using block devices without instance specific configs or devicetree defined.