[Xen-changelog] [xen staging] xen/arm32: head: Rework UART initialization on boot CPU

[patchbot@xxxxxxx]

commit f68eece73c69bbb9686def0980b252cd17f8e130
Author:     Julien Grall <julien.grall@xxxxxxx>
AuthorDate: Mon Apr 15 22:16:25 2019 +0100
Commit:     Julien Grall <julien.grall@xxxxxxx>
CommitDate: Sat Sep 7 12:10:16 2019 +0100

    xen/arm32: head: Rework UART initialization on boot CPU
    
    Anything executed after the label common_start can be executed on all
    CPUs. However most of the instructions executed between the label
    common_start and init_uart are not executed on the boot CPU.
    
    The only instructions executed are to lookup the CPUID so it can be
    printed on the console (if earlyprintk is enabled). Printing the CPUID
    is not entirely useful to have for the boot CPU and requires a
    conditional branch to bypass unused instructions.
    
    Furthermore, the function init_uart is only called for boot CPU
    requiring another conditional branch. This makes the code a bit tricky
    to follow.
    
    The UART initialization is now moved before the label common_start. This
    now requires to have a slightly altered print for the boot CPU and set
    the early UART base address in each the two path (boot CPU and
    secondary CPUs).
    
    This has the nice effect to remove a couple of conditional branch in
    the code.
    
    After this rework, the CPUID is only used at the very beginning of the
    secondary CPUs boot path. So there is no need to "reserve" x24 for the
    CPUID.
    
    Lastly, take the opportunity to replace load from literal pool with the
    new macro mov_w.
    
    Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/arm32/head.S | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index b54331c19d..fd3a273550 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -54,7 +54,7 @@
  *   r4  -
  *   r5  -
  *   r6  - identity map in place
- *   r7  - CPUID
+ *   r7  -
  *   r8  - DTB address (boot CPU only)
  *   r9  - paddr(start)
  *   r10 - phys offset
@@ -123,6 +123,12 @@ past_zImage:
         add   r8, r10                /* r8 := paddr(DTB) */
 #endif
 
+        /* Initialize the UART if earlyprintk has been enabled. */
+#ifdef CONFIG_EARLY_PRINTK
+        bl    init_uart
+#endif
+        PRINT("- Boot CPU booting -\r\n")
+
         mov   r12, #0                /* r12 := is_secondary_cpu */
 
         b     common_start
@@ -137,14 +143,9 @@ GLOBAL(init_secondary)
 
         mov   r12, #1                /* r12 := is_secondary_cpu */
 
-common_start:
         mrc   CP32(r1, MPIDR)
         bic   r7, r1, #(~MPIDR_HWID_MASK) /* Mask out flags to get CPU ID */
 
-        /* Non-boot CPUs wait here until __cpu_up is ready for them */
-        teq   r12, #0
-        beq   1f
-
         ldr   r0, =smp_up_cpu
         add   r0, r0, r10            /* Apply physical offset */
         dsb
@@ -156,15 +157,14 @@ common_start:
 1:
 
 #ifdef CONFIG_EARLY_PRINTK
-        ldr   r11, =EARLY_UART_BASE_ADDRESS  /* r11 := UART base address */
-        teq   r12, #0                /* Boot CPU sets up the UART too */
-        bleq  init_uart
+        mov_w r11, EARLY_UART_BASE_ADDRESS   /* r11 := UART base address */
         PRINT("- CPU ")
         mov   r0, r7
         bl    putn
         PRINT(" booting -\r\n")
 #endif
 
+common_start:
         /* Check that this CPU has Hyp mode */
         mrc   CP32(r0, ID_PFR1)
         and   r0, r0, #0xf000        /* Bits 12-15 define virt extensions */
@@ -497,11 +497,15 @@ ENTRY(switch_ttbr)
 
 #ifdef CONFIG_EARLY_PRINTK
 /*
- * Bring up the UART.
- * r11: Early UART base address
- * Clobbers r0-r2
+ * Initialize the UART. Should only be called on the boot CPU.
+ *
+ * Output:
+ *  r11: Early UART base physical address
+ *
+ * Clobbers r0 - r3
  */
 init_uart:
+        mov_w r11, EARLY_UART_BASE_ADDRESS
 #ifdef EARLY_PRINTK_INIT_UART
         early_uart_init r11, r1, r2
 #endif
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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