Re: [PATCH v2 1/3] serial: core: Forget the RS485 GPIO descriptors when a port is removed

[sashiko-bot@kernel.org]

> The RS485 termination and RX-during-TX GPIO descriptors are acquired
> with devm on behalf of the port's device in uart_get_rs485_mode() and
> stored in struct uart_port, but nothing ever clears them. A uart_port
> can outlive the device it was registered with: the 8250 core keeps its
> ports in a static array, re-adds an unregistered entry as a placeholder
> and hands it to the next device that claims the slot. If that device
> has no RS485 support or no firmware node, uart_get_rs485_mode() returns
> before acquiring anything and the stale descriptors stay in place,
> pointing at lines that devres has already released. Enabling RS485 on
> such a port then drives GPIO lines the port no longer owns. The same
> happens when uart_get_rs485_mode() itself fails after the first
> descriptor was acquired.
> 
> Forget the descriptors when a port is removed, on entry to
> uart_get_rs485_mode() and on its error paths, so a port only ever
> carries descriptors acquired for its current device.
> 
> Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261105-serial-rs485-mode-gpio-v2-0-027e5348892f@vaisala.com?part=1