From: Jacob Abrams <satur9nine@gmail.com>

SW modifying USART_CR1 TE bit should cuase HW to respond by altering
USART_ISR TEACK bit, and likewise for RE and REACK bit.

This resolves some but not all issues necessary for the official STM USART
HAL driver to function as is.

Fixes: 87b77e6e01ca ("hw/char/stm32l4x5_usart: Enable serial read and write")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2540
Signed-off-by: Jacob Abrams <satur9nine@gmail.com>
Message-id: 20240911043255.51966-1-satur9nine@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
(cherry picked from commit 6cce0dcc6f7aaaeb7f17577776da510b04f67c99)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/char/stm32l4x5_usart.c b/hw/char/stm32l4x5_usart.c
index fc5dcac0c4..3cf200c080 100644
--- a/hw/char/stm32l4x5_usart.c
+++ b/hw/char/stm32l4x5_usart.c
@@ -154,6 +154,21 @@ REG32(RDR, 0x24)
 REG32(TDR, 0x28)
     FIELD(TDR, TDR, 0, 9)
 
+static void stm32l4x5_update_isr(Stm32l4x5UsartBaseState *s)
+{
+    if (s->cr1 & R_CR1_TE_MASK) {
+        s->isr |= R_ISR_TEACK_MASK;
+    } else {
+        s->isr &= ~R_ISR_TEACK_MASK;
+    }
+
+    if (s->cr1 & R_CR1_RE_MASK) {
+        s->isr |= R_ISR_REACK_MASK;
+    } else {
+        s->isr &= ~R_ISR_REACK_MASK;
+    }
+}
+
 static void stm32l4x5_update_irq(Stm32l4x5UsartBaseState *s)
 {
     if (((s->isr & R_ISR_WUF_MASK) && (s->cr3 & R_CR3_WUFIE_MASK))        ||
@@ -456,6 +471,7 @@ static void stm32l4x5_usart_base_write(void *opaque, hwaddr addr,
     case A_CR1:
         s->cr1 = value;
         stm32l4x5_update_params(s);
+        stm32l4x5_update_isr(s);
         stm32l4x5_update_irq(s);
         return;
     case A_CR2:
diff --git a/tests/qtest/stm32l4x5_usart-test.c b/tests/qtest/stm32l4x5_usart-test.c
index 8902518233..0630f8d53b 100644
--- a/tests/qtest/stm32l4x5_usart-test.c
+++ b/tests/qtest/stm32l4x5_usart-test.c
@@ -36,6 +36,8 @@ REG32(GTPR, 0x10)
 REG32(RTOR, 0x14)
 REG32(RQR, 0x18)
 REG32(ISR, 0x1C)
+    FIELD(ISR, REACK, 22, 1)
+    FIELD(ISR, TEACK, 21, 1)
     FIELD(ISR, TXE, 7, 1)
     FIELD(ISR, RXNE, 5, 1)
     FIELD(ISR, ORE, 3, 1)
@@ -191,7 +193,7 @@ static void init_uart(QTestState *qts)
 
     /* Enable the transmitter, the receiver and the USART. */
     qtest_writel(qts, (USART1_BASE_ADDR + A_CR1),
-        R_CR1_UE_MASK | R_CR1_RE_MASK | R_CR1_TE_MASK);
+        cr1 | R_CR1_UE_MASK | R_CR1_RE_MASK | R_CR1_TE_MASK);
 }
 
 static void test_write_read(void)
@@ -296,6 +298,37 @@ static void test_send_str(void)
     qtest_quit(qts);
 }
 
+static void test_ack(void)
+{
+    uint32_t cr1;
+    uint32_t isr;
+    QTestState *qts = qtest_init("-M b-l475e-iot01a");
+
+    init_uart(qts);
+
+    cr1 = qtest_readl(qts, (USART1_BASE_ADDR + A_CR1));
+
+    /* Disable the transmitter and receiver. */
+    qtest_writel(qts, (USART1_BASE_ADDR + A_CR1),
+        cr1 & ~(R_CR1_RE_MASK | R_CR1_TE_MASK));
+
+    /* Test ISR ACK for transmitter and receiver disabled */
+    isr = qtest_readl(qts, (USART1_BASE_ADDR + A_ISR));
+    g_assert_false(isr & R_ISR_TEACK_MASK);
+    g_assert_false(isr & R_ISR_REACK_MASK);
+
+    /* Enable the transmitter and receiver. */
+    qtest_writel(qts, (USART1_BASE_ADDR + A_CR1),
+        cr1 | (R_CR1_RE_MASK | R_CR1_TE_MASK));
+
+    /* Test ISR ACK for transmitter and receiver disabled */
+    isr = qtest_readl(qts, (USART1_BASE_ADDR + A_ISR));
+    g_assert_true(isr & R_ISR_TEACK_MASK);
+    g_assert_true(isr & R_ISR_REACK_MASK);
+
+    qtest_quit(qts);
+}
+
 int main(int argc, char **argv)
 {
     int ret;
@@ -308,6 +341,7 @@ int main(int argc, char **argv)
     qtest_add_func("stm32l4x5/usart/send_char", test_send_char);
     qtest_add_func("stm32l4x5/usart/receive_str", test_receive_str);
     qtest_add_func("stm32l4x5/usart/send_str", test_send_str);
+    qtest_add_func("stm32l4x5/usart/ack", test_ack);
     ret = g_test_run();
 
     return ret;
-- 
2.39.5