Re: [PATCH v2] ns16550: enable memory decoding on MMIO-based PCI console card

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Tue, May 02, 2023 at 12:53:15PM +0200, Jan Beulich wrote:
> On 25.04.2023 16:39, Marek Marczykowski-Górecki wrote:
> > pci_serial_early_init() enables PCI_COMMAND_IO for IO-based UART
> > devices, add setting PCI_COMMAND_MEMORY for MMIO-based UART devices too.
> 
> This sentence is odd, as by its grammar it looks to describe the current
> situation only. The respective sentence in v1 did not have this issue.
> 
> > --- a/xen/drivers/char/ns16550.c
> > +++ b/xen/drivers/char/ns16550.c
> > @@ -272,7 +272,15 @@ static int cf_check ns16550_getc(struct serial_port *port, char *pc)
> >  static void pci_serial_early_init(struct ns16550 *uart)
> >  {
> >  #ifdef NS16550_PCI
> > -    if ( !uart->ps_bdf_enable || uart->io_base >= 0x10000 )
> > +    if ( uart->bar )
> > +    {
> > +        pci_conf_write16(PCI_SBDF(0, uart->ps_bdf[0], uart->ps_bdf[1],
> > +                                  uart->ps_bdf[2]),
> > +                         PCI_COMMAND, PCI_COMMAND_MEMORY);
> > +        return;
> > +    }
> > +
> > +    if ( !uart->ps_bdf_enable )
> >          return;
> >  
> >      if ( uart->pb_bdf_enable )
> 
> While I did suggest using uart->bar, my implication was that the io_base
> check would then remain in place. Otherwise, if I'm not mistaken, MMIO-
> based devices not specified via "com<N>=...,pci" would then wrongly take
> the I/O port path.

I don't think MMIO-based devices specified manually have great chance to
work anyway (see the commit message), but indeed I shouldn't have broken
them even more.

> Furthermore - you can't use uart->bar alone here, can you? The field is
> set equally for MMIO and port based cards in pci_uart_config().

Right, I'll restore the io_base check.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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