linux-kernel - Re: [PATCH] ARM: at91: debug: use DEBUG_UART

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Date:	Tue, 7 Jun 2016 18:23:01 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Nicolas Ferre <nicolas.ferre@...el.com>
Cc:	Russell King <linux@...linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: at91: debug: use DEBUG_UART_VIRT

On 07/06/2016 at 17:48:21 +0200, Nicolas Ferre wrote :
> Le 07/06/2016 17:24, Alexandre Belloni a écrit :
> > AT91 still uses an offset (0x0100 0000) from the physical address to map
> > the debug UART. This is unfortunate as for some platforms (sama5d3 and
> > earlier), it ends up in the PCI zone and PCI is enabled in multi_v7.
> > Switch to DEBUG_UART_VIRT to solve that.
> > 
> > Tested on sama5d3 and 9g20.
> > 
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> 
> People using their old defconfigs must pay attention to this change...
> but it's true that it's a debug configuration anyway...
> 

I really doubt people are letting DEBUG_LL enabled in a production
kernel...

> > diff --git a/arch/arm/include/debug/at91.S b/arch/arm/include/debug/at91.S
> > index d4ae3b8e2426..0098401e5aeb 100644
> > --- a/arch/arm/include/debug/at91.S
> > +++ b/arch/arm/include/debug/at91.S
> > @@ -9,14 +9,6 @@
> >   *
> >  */
> >  
> > -#ifdef CONFIG_MMU
> > -#define AT91_IO_P2V(x) ((x) - 0x01000000)
> > -#else
> > -#define AT91_IO_P2V(x) (x)
> > -#endif
> > -
> > -#define AT91_DEBUG_UART_VIRT AT91_IO_P2V(CONFIG_DEBUG_UART_PHYS)
> > -
> >  #define AT91_DBGU_SR		(0x14)	/* Status Register */
> >  #define AT91_DBGU_THR		(0x1c)	/* Transmitter Holding Register */
> >  #define AT91_DBGU_TXRDY		(1 << 1)	/* Transmitter Ready */
> > @@ -24,7 +16,7 @@
> >  
> >  	.macro	addruart, rp, rv, tmp
> >  	ldr	\rp, =CONFIG_DEBUG_UART_PHYS		@ System peripherals (phys address)
> > -	ldr	\rv, =AT91_DEBUG_UART_VIRT		@ System peripherals (virt address)
> > +	ldr	\rv, =CONFIG_DEBUG_UART_VIRT		@ System peripherals (virt address)
> 
> Shouldn't we protect the use of this defined value with some
> #warning "Beware the value CONFIG_DEBUG_UART_VIRT haven't been defined:
> is it intentional"
> or even #error?
> 
> or something like that?
> 

Well, those that are using this feature are supposed to know what they
are doing. There is now protection for CONFIG_DEBUG_UART_PHYS anyway.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com