Re: [Xen-devel] [PATCH 2/2] xen: arm: more flexible scheme for specifying early printk device

[Tim Deegan <tim@xxxxxxx>]

At 16:51 +0000 on 12 Mar (1426175517), Ian Campbell wrote:
> On Thu, 2015-03-12 at 12:03 +0100, Tim Deegan wrote:
> > CONFIG_EARLY_PRINTK := $(or $(EARLY_PRINTK_$(CONFIG_EARLY_PRINTK)), 
> > $(CONFIG_EARLY_PRINTK)
> > EARLY_PRINTK_CFG := $(subst $(COMMA), ,$(CONFIG_EARLY_PRINTK))
> 
> I didn't know about $(or ...) (but I suppose I could have guessed it
> existed, I wonder since when though).

Since 3.81 (April 2006), it seems, so OK for debians back to squeeze.
We don't specify a gmake version, but that's very slightly newer than
GCC 4.1.

> In my early testing I found that 
>       CONFIG_EARLY_PRINTK := $(EARLY_PRINTK_$(CONFIG_EARLY_PRINTK))
> didn't do as I expected with CONFIG_EARLY_PRINTK on the make command
> line, but it's possible I messed up the trial.
> 
> > Or maybe not, now that I've written it out. :) Either way is probably fine.
> 
> :-)
> 
> I could do:
> 
> EARLY_PRINTK_CFG := $(subst $(COMMA), ,$(or 
> $(EARLY_PRINTK_$(CONFIG_EARLY_PRINTK)),
>                                             $(CONFIG_EARLY_PRINTK)))
> 
> Not sure that's better either.

Yep, or use another intermediate variable.  The bikeshed will look
lovely.

Tim.

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