[PATCH resend 2/2] env: add CONFIG_ENV_SECT_SIZE_AUTO

[Tom Rini <trini@konsulko.com>]

On Wed, Apr 14, 2021 at 08:51:43PM +0200, Rasmus Villemoes wrote:

> This is roughly the U-Boot side equivalent to commit
> e282c422e0 (tools: fw_env: use erasesize from MEMGETINFO ioctl). The
> motivation is the case where one has a board with several revisions,
> where the SPI flashes have different erase sizes.
> 
> In our case, we have an 8K environment, and the flashes have erase
> sizes of 4K (newer boards) and 64K (older boards). Currently, we must
> set CONFIG_ENV_SECT_SIZE to 64K to make the code work on the older
> boards, but for the newer ones, that ends up wasting quite a bit of
> time reading/erasing/restoring the last 56K.
> 
> At first, I wanted to allow setting CONFIG_ENV_SECT_SIZE to 0 to mean
> "use the erase size the chip reports", but that config
> option is used in a number of preprocessor conditionals, and shared
> between ENV_IS_IN_FLASH and ENV_IS_IN_SPI_FLASH.
> 
> So instead, introduce a new boolean config option, which for now can
> only be used with ENV_IS_IN_SPI_FLASH. If left off, there's no change
> in behaviour.
> 
> The only slightly annoying detail is that, when selected, the compiler
> is apparently not smart enough to see that the the saved_size and
> saved_offset variables are only used under the same "if (sect_size >
> CONFIG_ENV_SIZE)" condition as where they are computed, so we need to
> initialize them to 0 to avoid "may be used uninitialized" warnings.
> 
> On our newer boards with the 4K erase size, saving the environment now
> takes 0.080 seconds instead of 0.53 seconds, which directly translates
> to that much faster boot time since our logic always causes the
> environment to be written during boot.
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

Applied to u-boot/master, thanks!

-- 
Tom
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