On Wed, 16 Nov 2022, Pavel Machek wrote:
From: Maciej W. Rozycki macro@orcam.me.uk
[ Upstream commit 9906890c89e4dbd900ed87ad3040080339a7f411 ]
A SERIAL_8250_16550A_VARIANTS configuration option has been recently defined that lets one request the 8250 driver not to probe for 16550A device features so as to reduce the driver's device startup time in virtual machines.
Some actual hardware devices require these features to have been fully determined however for their driver to work correctly, so define a flag to let drivers request full 16550A feature probing on a device-by-device basis if required regardless of the SERIAL_8250_16550A_VARIANTS option setting chosen.
Fixes: dc56ecb81a0a ("serial: 8250: Support disabling mdelay-filled probes of 16550A variants") Cc: stable@vger.kernel.org # v5.6+
You said you'd drop this. It is still unused in 5.10.155, as flag is never set.
Right. Technically it fixes a problem introduced in v5.6, but it wasn't exposed until commit 00b7a4d4ee42 ("serial: 8250: Request full 16550A feature probing for OxSemi PCIe devices") in v5.19 (unless, of course another UART broke that we don't know of). I agree it's OK to drop this change in this case.
Maciej