Re: [PATCH v7 5/6] serial: Support for RS-485 multipoint addresses

Andy Shevchenko
2022-06-15T14:14:27Z

On Wed, Jun 15, 2022 at 03:48:28PM +0300, Ilpo Järvinen wrote:
> Add support for RS-485 multipoint addressing using 9th bit [*]. The
> addressing mode is configured through .rs485_config().
>
> ADDRB in termios indicates 9th bit addressing mode is enabled. In this
> mode, 9th bit is used to indicate an address (byte) within the
> communication line. ADDRB can only be enabled/disabled through
> .rs485_config() that is also responsible for setting the destination and
> receiver (filter) addresses.
>
> [*] Technically, RS485 is just an electronic spec and does not itself
> specify the 9th bit addressing mode but 9th bit seems at least
> "semi-standard" way to do addressing with RS485.
>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: linux-api@vger.kernel.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-arch@vger.kernel.org

Hmm... In order to reduce commit messages you can move these Cc:s after the
cutter line ('---').

...

> - __u32 padding[5]; /* Memory is cheap, new structs
> - are a royal PITA .. */
> + __u8 addr_recv;
> + __u8 addr_dest;
> + __u8 padding[2 + 4 * sizeof(__u32)]; /* Memory is cheap, new structs
> + * are a royal PITA .. */

I'm not sure it's an equivalent. I would leave u32 members untouched, so
something like

__u8 addr_recv;
__u8 addr_dest;
__u8 padding0[2]; /* Memory is cheap, new structs
__u32 padding1[4]; * are a royal PITA .. */

And repeating about `pahole` tool which may be useful here to check for ABI
potential changes.

--
With Best Regards,
Andy Shevchenko