Re: [PATCH 0/2] serial: 8250: Let drivers request full 16550A feature probing

[Josh Triplett]

On September 17, 2022 11:07:18 AM GMT+01:00, "Maciej W. Rozycki" <macro@xxxxxxxxxxx> wrote:
>Hi,
>
> A recent change has added a SERIAL_8250_16550A_VARIANTS option, which 
>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.  
>This has turned out problematic to a more recent update for the OxSemi 
>Tornado series PCIe devices, whose new baud rate generator handling code 
>actually requires switching hardware into the enhanced mode for correct 
>operation, which actually requires 16550A device features to have been 
>probed for.
>
> This small patch series fixes the issue by letting individual device 
>subdrivers to request full 16550A device feature probing by means of a 
>flag regardless of the SERIAL_8250_16550A_VARIANTS setting chosen.
>
> The changes have been verified with an OXPCIe952 device, in the native 
>UART mode and a 64-bit RISC-V system as well as in the legacy UART mode 
>and a 32-bit x86 system.

Seems reasonable to me, as long as the flag is only set by drivers that know they've found their hardware.