[RFC PATCH] tests/qtest/stm32l4x5_usart: Avoid accessing NVIC via MMIO

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

The STM32L4x5 SoC family use a ARM Cortex-M core. Such
core is architecturally tied with a NVIC (interrupt controller),
having the NVIC MMIO mapped in the core address space.

When using the QTest accelerator, we don't emulate vCPU, only
a dummy is created. For now, QTest is only supposed to access
MMIO devices mapped on the main 'SysBus'. Thus it shouldn't
be able to access a NVIC MMIO region, because such region is
specific to a vCPU address space, which isn't available under
QTest.

In order to avoid NVIC MMIO accesses, rather than checking
UART IRQs on the NVIC, intercept the UART IRQ and check for
raised/lowered events.

The sysbus USART1 IRQ output is wired to EXTI #26 input.
Use qtest_irq_intercept_out_named() to intercept it, count
the events with qtest_get_irq_lowered_counter() and
qtest_get_irq_raised_counter().

Remove the then unused check/clear_nvic_pending() methods.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
Based-on: <20241216141818.111255-7-gustavo.romero@linaro.org>
"tests/qtest: Add API functions to capture IRQ toggling"

This patch is to fix the problem reported by Fabiano when
removing the &first_cpu global in qtest, see analysis in:
https://lore.kernel.org/qemu-devel/05820c9b-a683-4eb4-a836-e97aa708d5e5@linaro.org/

Note, while writing that patch I noticed a problem with the
b-l475e-iot01a machine. In bl475e_init() somes output GPIOs
are wired twice. The EXTI outputs are passed to the SoC with
qdev_pass_gpios(), and few are re-wired to the various output
IRQ splitters. I'll open a GitLab issue so it can be cleared
later.
---
 tests/qtest/stm32l4x5_usart-test.c | 33 +++++++-----------------------
 1 file changed, 7 insertions(+), 26 deletions(-)

diff --git a/tests/qtest/stm32l4x5_usart-test.c b/tests/qtest/stm32l4x5_usart-test.c
index 927bab63614..35622e9434d 100644
--- a/tests/qtest/stm32l4x5_usart-test.c
+++ b/tests/qtest/stm32l4x5_usart-test.c
@@ -46,26 +46,7 @@ REG32(ICR, 0x20)
 REG32(RDR, 0x24)
 REG32(TDR, 0x28)
 
-#define NVIC_ISPR1 0XE000E204
-#define NVIC_ICPR1 0xE000E284
-#define USART1_IRQ 37
-
-static bool check_nvic_pending(QTestState *qts, unsigned int n)
-{
-    /* No USART interrupts are less than 32 */
-    assert(n > 32);
-    n -= 32;
-    return qtest_readl(qts, NVIC_ISPR1) & (1 << n);
-}
-
-static bool clear_nvic_pending(QTestState *qts, unsigned int n)
-{
-    /* No USART interrupts are less than 32 */
-    assert(n > 32);
-    n -= 32;
-    qtest_writel(qts, NVIC_ICPR1, (1 << n));
-    return true;
-}
+#define USART1_EXTI_IRQ 26
 
 /*
  * Wait indefinitely for the flag to be updated.
@@ -195,6 +176,8 @@ static void init_uart(QTestState *qts)
     /* Enable the transmitter, the receiver and the USART. */
     qtest_writel(qts, (USART1_BASE_ADDR + A_CR1),
         cr1 | R_CR1_UE_MASK | R_CR1_RE_MASK | R_CR1_TE_MASK);
+
+    qtest_irq_intercept_out_named(qts, "machine/soc/exti", "sysbus-irq");
 }
 
 static void test_write_read(void)
@@ -221,7 +204,7 @@ static void test_receive_char(void)
     g_assert_true(send(sock_fd, "a", 1, 0) == 1);
     usart_wait_for_flag(qts, USART1_BASE_ADDR + A_ISR, R_ISR_RXNE_MASK);
     g_assert_cmphex(qtest_readl(qts, USART1_BASE_ADDR + A_RDR), ==, 'a');
-    g_assert_false(check_nvic_pending(qts, USART1_IRQ));
+    g_assert_cmpuint(qtest_get_irq_lowered_counter(qts, USART1_EXTI_IRQ), ==, 0);
 
     /* Now with the IRQ */
     cr1 = qtest_readl(qts, (USART1_BASE_ADDR + A_CR1));
@@ -230,8 +213,7 @@ static void test_receive_char(void)
     g_assert_true(send(sock_fd, "b", 1, 0) == 1);
     usart_wait_for_flag(qts, USART1_BASE_ADDR + A_ISR, R_ISR_RXNE_MASK);
     g_assert_cmphex(qtest_readl(qts, USART1_BASE_ADDR + A_RDR), ==, 'b');
-    g_assert_true(check_nvic_pending(qts, USART1_IRQ));
-    clear_nvic_pending(qts, USART1_IRQ);
+    g_assert_cmpuint(qtest_get_irq_lowered_counter(qts, USART1_EXTI_IRQ), >, 0);
 
     close(sock_fd);
 
@@ -251,7 +233,7 @@ static void test_send_char(void)
     qtest_writel(qts, USART1_BASE_ADDR + A_TDR, 'c');
     g_assert_true(recv(sock_fd, s, 1, 0) == 1);
     g_assert_cmphex(s[0], ==, 'c');
-    g_assert_false(check_nvic_pending(qts, USART1_IRQ));
+    g_assert_cmpuint(qtest_get_irq_lowered_counter(qts, USART1_EXTI_IRQ), ==, 0);
 
     /* Now with the IRQ */
     cr1 = qtest_readl(qts, (USART1_BASE_ADDR + A_CR1));
@@ -260,8 +242,7 @@ static void test_send_char(void)
     qtest_writel(qts, USART1_BASE_ADDR + A_TDR, 'd');
     g_assert_true(recv(sock_fd, s, 1, 0) == 1);
     g_assert_cmphex(s[0], ==, 'd');
-    g_assert_true(check_nvic_pending(qts, USART1_IRQ));
-    clear_nvic_pending(qts, USART1_IRQ);
+    g_assert_cmpuint(qtest_get_irq_raised_counter(qts, USART1_EXTI_IRQ), >, 0);
 
     close(sock_fd);
 
-- 
2.47.1