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

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Message-ID: <20220825195143.GA2867872@bhelgaas>
Date:   Thu, 25 Aug 2022 14:51:43 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Peter Zijlstra <peterz@...radead.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 09:36:35PM +0200, Peter Zijlstra wrote:
> 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'.

Personally, I would spell it out just to make it less arcane.  I
wouldn't know where to find the definition, and the PCI specs don't
seem to use the abbreviation.  But no big deal either way.

Bjorn