linux-kernel - Re: [PATCH] m68k/mac: Allocate IOP message pool and queues dynamically

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Date:	Mon, 1 Jul 2013 17:48:22 +1000 (EST)
From:	Finn Thain <fthain@...egraphics.com.au>
To:	Brad Boyer <flar@...andria.com>
cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k/mac: Allocate IOP message pool and queues
 dynamically

On Sun, 30 Jun 2013, Brad Boyer wrote:

> On Sun, Jun 30, 2013 at 12:02:22PM +0200, Geert Uytterhoeven wrote:
> >  
> >  	if (iop_scc_present) {
> >  		printk("IOP: detected SCC IOP at %p\n", iop_base[IOP_NUM_SCC]);
> > +		alloc_msg_queue(IOP_NUM_SCC);
> 
> Technically, this isn't actually useful. As long as we never start this
> IOP, it can't ever send or be sent any messages.

That assumes that the SCC IOP is in a stopped state after iop_preinit(). 
But I don't think that's the case. If it is technically possible to 
exchange messages with a device in bypass mode (?) then I think the code 
above is correct.

> > @@ -315,6 +307,9 @@ void __init iop_register_interrupts(void)
> >  		} else {
> >  			printk("IOP: the ISM IOP seems to be alive.\n");
> >  		}
> 
> The if/else above isn't useful if it is run before the call to 
> iop_start. However, it's also useless if it is called immediately after 
> the call to iop_alive which is now below. It was supposed to eventually 
> be called in the background on a regular schedule, but that never 
> happened.
> 

I agree. That if/else statement and the conditional printk's should be 
omitted.

I had thought that in the existing code the interrupt service routine was 
registered before the call to iop_start() but in fact iop_start() happens 
first. Looks like a bug to me. The interrupt handler needs to be able to 
acknowledge unsolicited messages...

Finn
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