tests/qtest/boot-serial-test: Initialize PL011 Control register

The tests using the PL011 UART of the virt and raspi machines
weren't properly enabling the UART and its transmitter previous
to sending characters. Follow the PL011 manual initialization
recommendation by setting the proper bits of the control register.

Update the ASM code prefixing:

  *UART_CTRL = UART_ENABLE | TX_ENABLE;

to:

  while (true) {
      *UART_DATA = 'T';
  }

Note, since commit 51b61dd ("hw/char/pl011: Warn when using
disabled transmitter") incomplete PL011 initialization can be
logged using the '-d guest_errors' command line option.

Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>

Author: philmd

tests/qtest/boot-serial-test.c

@@ -70,15 +70,20 @@ static const uint8_t kernel_plml605[] = {
 };
 
 static const uint8_t bios_raspi2[] = {
-    0x08, 0x30, 0x9f, 0xe5,                 /*        ldr     r3, [pc, #8]   Get &UART0 */
+    0x10, 0x30, 0x9f, 0xe5,                 /*        ldr     r3, [pc, #16]  Get &UART0 */
+    0x10, 0x20, 0x9f, 0xe5,                 /*        ldr     r2, [pc, #16]  Get &CR */
+    0xb0, 0x23, 0xc3, 0xe1,                 /*        strh    r2, [r3, #48]  Set CR */
     0x54, 0x20, 0xa0, 0xe3,                 /*        mov     r2, #'T' */
     0x00, 0x20, 0xc3, 0xe5,                 /* loop:  strb    r2, [r3]       *TXDAT = 'T' */
     0xff, 0xff, 0xff, 0xea,                 /*        b       -4             (loop) */
     0x00, 0x10, 0x20, 0x3f,                 /* UART0: 0x3f201000 */
+    0x01, 0x01, 0x00, 0x00,                 /* CR:    0x101 = UARTEN|TXE */
 };
 
 static const uint8_t kernel_aarch64[] = {
     0x02, 0x20, 0xa1, 0xd2,                 /*        mov    x2, #0x9000000  Load UART0 */
+    0x21, 0x20, 0x80, 0x52,                 /*        mov    w1, 0x101       CR = UARTEN|TXE */
+    0x41, 0x60, 0x00, 0x79,                 /*        strh   w1, [x2, #48]   Set CR */
     0x81, 0x0a, 0x80, 0x52,                 /*        mov    w1, #'T' */
     0x41, 0x00, 0x00, 0x39,                 /* loop:  strb   w1, [x2]        *TXDAT = 'T' */
     0xff, 0xff, 0xff, 0x17,                 /*        b      -4              (loop) */