Re: [PATCH] mos6522: remove anh register

[Philippe Mathieu-Daudé]

On 12/14/19 11:47 AM, Mark Cave-Ayland wrote:
> On 13/12/2019 08:45, Laurent Vivier wrote:
> > Le 13/12/2019 à 02:44, David Gibson a écrit :
> > > On Thu, Dec 12, 2019 at 08:43:59PM +0100, Laurent Vivier wrote:
> > > > Register addr 1 is defined as buffer A with handshake (vBufAH),
> > > > register addr 15 is also defined as buffer A without handshake (vBufA).
> > > >
> > > > Linux kernel has a big "DON'T USE!" next to the register 1 addr
> > > > definition (vBufAH), and only uses register 15 (vBufA).
> > > >
> > > > So remove the definition of 'anh' and use only 'a' (with VIA_REG_ANH and
> > > > VIA_REG_A).
> > >
> > > I'm not actually following the rationale for removing the register.
> > > Linux doesn't use it, but if it's part of the real hardware model we
> > > should keep it, no?
> >
> > It's actually two methods to access the same register (with handshake,
> > without handshake).
> >
> > In the datashit Register 15 is described as "Same as register 1 except
> > no handshake".
>
> Indeed, certainly my reading of the specification was that it was the same 
> register.
> I'd be inclined to add qemu_log() at unimp for the handshake registers so at 
> least we
> can easily spot if anything is using them.

Agreed, clever than my review suggestion.

     case VIA_REG_A:
+        qemu_log_mask(LOG_UNIMP, ...);
+        /* fall through */
+    case VIA_REG_ANH:
         val = s->a;
         break;