arm/early-printk: allow skipping of UART init

While it seems obvious to initialize the UART before using it, chances
are that some firmware code or the bootloader already did this.
So it may actually be a good idea to skip the initialization, in fact
this fixes early printk on my TC2 Versatile Express.
So provide an option in xen/arch/arm/Rules.mk to only initialize the
UART when needed.

Signed-off-by: Andre Przywara <andre.przywara@calxeda.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/docs/misc/arm/early-printk.txt b/docs/misc/arm/early-printk.txt
index 10c30531f6111cdb9004f18b1664bae2f0d74437..965add56b8122ff7366a75ae276a41b392e9a064 100644 (file)
--- a/docs/misc/arm/early-printk.txt
+++ b/docs/misc/arm/early-printk.txt
@@ -14,5 +14,9 @@ where mach is the name of the machine:
 
 The baud rate is hardcoded in xen/arch/arm/Rules.mk,
 see there when adding support for new machines.
+If not explicitly requested with "EARLY_PRINTK_INIT_UART := y" in Rules.mk,
+the code will not try to initialize the UART, so that bootloader or
+firmware settings can be used for maximum compatibility. The baud rate
+parameter is ignored in this case.
 
 By default early printk is disabled.

diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
index b4d690716a8f6288f8bae45b378e155d11e9ec15..fdcf73e453995577d6d8644aed8c2b7462f6f04c 100644 (file)
--- a/xen/arch/arm/Rules.mk
+++ b/xen/arch/arm/Rules.mk
@@ -49,6 +49,7 @@ EARLY_PRINTK_BAUD := 38400
 endif
 ifeq ($(CONFIG_EARLY_PRINTK), exynos5250)
 EARLY_PRINTK_INC := exynos4210
+EARLY_PRINTK_INIT_UART := y
 EARLY_PRINTK_BAUD := 115200
 endif
 
@@ -57,6 +58,7 @@ EARLY_PRINTK := y
 endif
 
 CFLAGS-$(EARLY_PRINTK) += -DEARLY_PRINTK
+CFLAGS-$(EARLY_PRINTK_INIT_UART) += -DEARLY_PRINTK_INIT_UART
 CFLAGS-$(EARLY_PRINTK) += -DEARLY_PRINTK_INC=\"debug-$(EARLY_PRINTK_INC).inc\"
 CFLAGS-$(EARLY_PRINTK) += -DEARLY_PRINTK_BAUD=$(EARLY_PRINTK_BAUD)
 endif

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index ec7f64061334aae4ee260de75e798a99ef5c8abb..0588d54709d7dd6a5a2f74f1033e875e5c1a5938 100644 (file)
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -369,7 +369,9 @@ fail:   PRINT("- Boot failed -\r\n")
  * r11: Early UART base address
  * Clobbers r0-r2 */
 init_uart:
+#ifdef EARLY_PRINTK_INIT_UART
         early_uart_init r11, r1, r2
+#endif
         adr   r0, 1f
         b     puts                  /* Jump to puts */
 1:      .asciz "- UART enabled -\r\n"

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 89559469ad13c2ba9673717c925d75074c95ce7a..21b7e4d7415033e162a7953d3cf4a1cc80e2128f 100644 (file)
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -116,7 +116,9 @@ boot_cpu:
 #ifdef EARLY_PRINTK
         ldr   x23, =EARLY_UART_BASE_ADDRESS /* x23 := UART base address */
         cbnz  x22, 1f
+#ifdef EARLY_PRINTK_INIT_UART
         bl    init_uart                 /* CPU 0 sets up the UART too */
+#endif
 1:      PRINT("- CPU ")
         mov   x0, x22
         bl    putn