Re: [PATCH v4 2/2] serial: 8250: add driver for KEBA UART

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Thu, Nov 27, 2025 at 08:40:41PM +0100, Gerhard Engleder wrote:
> On 26.11.25 22:33, Andy Shevchenko wrote:
> > On Wed, Nov 26, 2025 at 10:06:17PM +0100, Gerhard Engleder wrote:
> > > On 26.11.25 14:17, Andy Shevchenko wrote:
> > > > On Thu, Oct 23, 2025 at 05:12:29PM +0200, Gerhard Engleder wrote:

...

> > > > Can't you call uart_read_port_properties()?
> > > > 
> > > > If ever you gain some properties either via FW description or via software
> > > > nodes, they will be automatically used without need to update the driver!
> > > 
> > > Yes that would be some nice behavior. But __uart_read_properties()
> > > sets some defaults even if no firmware node exist (UPF_SHARE_IRQ,
> > 
> > Is it a problem? Even a single IRQ may be marked shared.
> > 
> > > 0 as irq number
> > 
> > It doesn't do that, it just skips setting it in that case.
> > 
> > > or it fails if not irq number is found).
> > 
> > Yeah, this is most "problematic" part in case of this driver. Why is it
> > auxiliary and not platform? With that the __uart_read_properties() needs
> > to be updated to also query IRQ from respective aux device, and aux dev
> > needs implementation of dev_is_auxiliary(). Not that big deal, though.
> 
> It is auxiliary and not platform, because gregkh suggested to switch
> from platform to auxiliary. IMO he is right and that is a better fit,
> because auxiliary devices were introduced to split big devices into
> sub devices, which results in smaller drivers with one job for the
> sub device. That's actually what I tried to do with platform devices
> first.
> 
> > > So __uart_read_properties() would need to be changed. IMO it makes no sense
> > > to change __uart_read_properties() as this functionality is currently
> > > not required.
> > 
> > Yes, but as I said it will give you for free the possibility to use those
> > properties without future modifications of the driver. OTOH, driver is in
> > tree and modifications will be needed one way or another :-)
> 
> Yes, if the KEBA UART changes, then modifications would be needed. We
> kept this UART stable now for over 10 years. As it is FPGA based, we
> can keep it stable as long as FPGAs are on the market. In industrial
> automation the products are in the field for 10 years, 20 years or even
> more. We can only support the devices for that long time by keeping
> them compatible. So I don't expect changes now and therefore I would
> not prepare for them.

Fair enough.

-- 
With Best Regards,
Andy Shevchenko