[U-Boot] [PATCH 5/5] Warn when the machine ID isn't passed to an ARM kernel and u-boot is compiled in debug mode. The kernel cannot boot without it.

[Jason]

On Mon, Jul 04, 2011 at 04:32:35PM -0400, Christopher Harvey wrote:
> On Mon, Jul 04, 2011 at 04:13:49PM -0400, Jason wrote:
> > On Mon, Jul 04, 2011 at 02:55:54PM -0400, Christopher Harvey wrote:
> > > On Mon, Jul 04, 2011 at 02:08:44PM -0400, Jason wrote:
> > > > On Mon, Jul 04, 2011 at 01:45:41PM -0400, Christopher Harvey wrote:
> > > > > +	   Hopefully there will never be this many machines. 
> > > > > +	   Can't use 0 since 0 is already used as a mach-type. */
> > > > > +	gd->bd->bi_arch_number = 0xffffffff; 
> > > > >  
> > > > >  	gd->bd->bi_baudrate = gd->baudrate;
> > > > >  	/* Ram ist board specific, so move it to board code ... */
> > > > > diff --git a/arch/arm/lib/bootm.c b/arch/arm/lib/bootm.c
> > > > > index 802e833..70b3b76 100644
> > > > > --- a/arch/arm/lib/bootm.c
> > > > > +++ b/arch/arm/lib/bootm.c
> > > > > @@ -113,6 +113,12 @@ int do_bootm_linux(int flag, int argc, char *argv[], bootm_headers_t *images)
> > > > >  		printf ("Using machid 0x%x from environment\n", machid);
> > > > >  	}
> > > > >  
> > > > > +#ifdef DEBUG
> > > > > +	if(machid==0xffffffff) {
> > > > > +	        debug("\nWarning: machid not set! Linux will not finish booting.\n\n");
> > > > 
> > > > s/finish/start/ ;-)
> > > >
> > > I'll have to disagree here.  Linux will decompress and some functions
> > > will run but it will eventually stop, hence will not finish.
> > 
> > On further investigation, you're right, it doesn't finish
> > starting/booting.  Sorry for the noise.
> > 
> > > > Also, shouldn't the compile fail in this case (#error)?  Or, at least #warn?
> > > >
> > > The compiler can't know what machid will be at runtime. Maybe a "would
> > > you like to continue?" prompt could work.
> > 
> > Since the kernel throws a nice fat error message when the MACH_TYPE
> > doesn't match what it was compiled for, I don't see the point to adding
> > another message at the same point in the development process.
> 
> I didn't see that message. Do you know what lines of code in the
> kernel print it? Or maybe just the message itself? 

In init/main.c
	start_kernel() calls
		setup_arch()

In arch/arm/kernel/setup.c
	setup_arch() calls
		setup_machine_tags() which calls
			dump_machine_table()

when the value in r1 doesn't match any of the mach-types the kernel was
compiled for.

> If the kernel can check the value why would it need to be passed 
> in the first place?

Because the kernel has no way of easily determining which arm board it's
running on without this feature.

hth,

Jason.