[PATCH] i2c: avoid dynamic stack use in dm_i2c_write

[Heiko Schocher]

Hello Rasmus,

On 07.07.22 15:12, Rasmus Villemoes wrote:
> The size of the dynamic stack allocation here is bounded by the if()
> statement. However, just allocating the maximum size up-front and
> doing malloc() if necessary avoids code duplication (the
> i2c_setup_offset() until the invocation of ->xfer), and generates much
> better (smaller) code:
> 
> bloat-o-meter drivers/i2c/i2c-uclass.o.{0,1}
> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-144 (-144)
> Function                                     old     new   delta
> dm_i2c_write                                 552     408    -144
> Total: Before=3828, After=3684, chg -3.76%
> 
> It also makes static analysis of maximum stack usage (using the .su
> files that are automatically generated during build) easier if there
> are no lines saying "dynamic".
> 
> [This is not entirely equivalent to the existing code; this now uses
> the stack for len <= 64 rather than len <= 63, but that seems like a
> more natural limit.]
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
> ---
>  drivers/i2c/i2c-uclass.c | 30 ++++++++++++------------------
>  1 file changed, 12 insertions(+), 18 deletions(-)

Looks good to me, nice catch!

Reviewed-by: Heiko Schocher <hs at denx.de>

bye,
Heiko
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