[02/10] ARM: zx: add low level debug support

Commit Message

Shawn Guo March 16, 2015, 2:37 a.m. UTC

On Sun, Mar 15, 2015 at 10:48:18PM +0000, Russell King - ARM Linux wrote:
> On Sat, Mar 14, 2015 at 07:49:37PM +0800, Jun Nie wrote:
> > Use the UART0 peripheral for low level debug. Only the UART port 0 is
> > currently supported.
> 
> None of this code is necessary - in fact, you don't have to add one line
> of assembly code what so ever.
> 
> We have generic PL011 debug support.  Please use that, you only need to
> ensure that the phys and virtual addresses are properly configured in
> arch/arm/Kconfig.debug and that the appropriate symbol is selected.

For some reason we never understood, ZTE designers chose to use a
different offset on Data and Flag register, which make it difficult to
reuse pl01x.S.

/* Data read or written from the interface. */
#define UART01x_DR	0x00
#define ZX_UART01x_DR	0x04

/* Flag register (Read only). */
#define ZX_UART01x_FR	0x14
#define UART01x_FR	0x18

We chose to duplicate the file to avoid churning generic pl01x.S.  Would
something like below be acceptable?  Or any better idea?



Shawn

Comments

Arnd Bergmann March 16, 2015, 10:08 a.m. UTC | #1

On Monday 16 March 2015 10:37:42 Shawn Guo wrote:
> 
> We chose to duplicate the file to avoid churning generic pl01x.S.  Would
> something like below be acceptable?  Or any better idea?
> 
> diff --git a/arch/arm/include/debug/pl01x.S b/arch/arm/include/debug/pl01x.S
> index 92ef808a2337..da83512c4788 100644
> --- a/arch/arm/include/debug/pl01x.S
> +++ b/arch/arm/include/debug/pl01x.S
> @@ -12,6 +12,13 @@
>  */
>  #include <linux/amba/serial.h>
>  
> +#ifdef CONFIG_ARCH_ZX
> +#undef UART01x_DR
> +#undef UART01x_FR
> +#define UART01x_DR     0x04
> +#define UART01x_FR     0x14
> +#endif
> +
>  #ifdef CONFIG_DEBUG_UART_PHYS
> 

This is almost right, but breaks a corner case where you want to debug
the boot on a platform other than ZX, but in a kernel that also has
ARCH_ZX enabled. I think the best way to solve this is to have
CONFIG_DEBUG_ZTE_ZX select CONFIG_DEBUG_UART_PL01X, and then
use #ifdef CONFIG_DEBUG_ZTE_ZX above rather than CONFIG_ARCH_ZX.

	Arnd

Patch

diff --git a/arch/arm/include/debug/pl01x.S b/arch/arm/include/debug/pl01x.S
index 92ef808a2337..da83512c4788 100644
--- a/arch/arm/include/debug/pl01x.S
+++ b/arch/arm/include/debug/pl01x.S
@@ -12,6 +12,13 @@ 
 */
 #include <linux/amba/serial.h>
 
+#ifdef CONFIG_ARCH_ZX
+#undef UART01x_DR
+#undef UART01x_FR
+#define UART01x_DR     0x04
+#define UART01x_FR     0x14
+#endif
+
 #ifdef CONFIG_DEBUG_UART_PHYS
                .macro  addruart, rp, rv, tmp
                ldr     \rp, =CONFIG_DEBUG_UART_PHYS