linux-kernel - Re: [PATCH] earlyprintk: Clean up pciserial

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Date:   Thu, 25 Aug 2022 21:36:35 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH] earlyprintk: Clean up pciserial

On Thu, Aug 25, 2022 at 12:39:59PM -0500, Bjorn Helgaas wrote:

> > -	   (((classcode >> 8) & 0xff) != 0x02)) /* 16550 I/F at BAR0 */ {

> > diff --git a/include/linux/pci_ids.h b/include/linux/pci_ids.h
> > index 6feade66efdb..1d2c7df8cd41 100644
> > --- a/include/linux/pci_ids.h
> > +++ b/include/linux/pci_ids.h
> > @@ -75,6 +75,9 @@
> >  #define PCI_CLASS_COMMUNICATION_MODEM	0x0703
> >  #define PCI_CLASS_COMMUNICATION_OTHER	0x0780
> >  
> > +/* I/F for SERIAL/MODEM */
> 
> I/F?  Grep says it's fairly common, but doesn't seem completely
> obvious.  I guess it means "interface"?

It does, I carried the nomenclature from the above line; happy to change
it if you want.

  https://wiki.osdev.org/PCI#Class_Codes

Calls it 'Prog IF'.

> > +#define PCI_SERIAL_16550_COMPATIBLE	0x02
> > +
> >  #define PCI_BASE_CLASS_SYSTEM		0x08
> >  #define PCI_CLASS_SYSTEM_PIC		0x0800
> >  #define PCI_CLASS_SYSTEM_PIC_IOAPIC	0x080010