Re: [PATCH 1/2] media: rkvdec: reduce excessive stack usage in assemble_hw_pps()

[David Laight <david.laight.linux@gmail.com>]

On Mon, 02 Feb 2026 16:59:05 +0100
"Arnd Bergmann" <arnd@arndb.de> wrote:

...
>  - Since most of the fields are exactly 6 bits offset from a word
>    boundary, you can try assembling all the  *_field_order_cnt*
>    fields in an array first that has all the bits in the correct
>    order, but then shift the entire array six bits.

How are they being written to the hardware?
It would be very unusual for hardware not to have things 'reasonably aligned'.
This makes me think that the data buffer is actually being 'bit-bashed'
down some serial data interface.
In which case the simple solution is to give the function that writes
the data a 'bit offset' for the first word.

And to re-iterate C bit-fields are completely non portable and entirely
inappropriate for mapping onto device registers.
You can use C structures (arranged with everything on its natural
boundary so there are no holes) with members declared with the correct
endianness.
Indeed that is actually preferable to using numeric constants as the
offsets are tied to the correct structure.

	David

> 
>       Arnd
>