[Qemu-devel] [Bug 1760262] [NEW] cmsdk-apb-uart doesn't appear to clear interrupt flags

[Patrick Oppenlander]

Public bug reported:

I have been writing a small operating system and using QEMU emulating
the mps2-an385 board for some of my testing.

During development of the uart driver I observed some odd behaviour with
the TX interrupt -- writing a '1' to bit 0 of the INTCLEAR register
doesn't clear the TX interrupt flag, and the interrupt fires
continuously.

It's possible that I have an error somewhere in my code, but after
inspecting the QEMU source it does appear to be a QEMU bug. I applied
the following patch and it solved my issue:

>From 9875839c144fa60a3772f16ae44d32685f9328aa Mon Sep 17 00:00:00 2001
From: Patrick Oppenlander <address@hidden>
Date: Sat, 31 Mar 2018 15:10:28 +1100
Subject: [PATCH] hw/char/cmsdk-apb-uart: fix clearing of interrupt flags

---
 hw/char/cmsdk-apb-uart.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/char/cmsdk-apb-uart.c b/hw/char/cmsdk-apb-uart.c
index 1ad1e14295..64991bd9d7 100644
--- a/hw/char/cmsdk-apb-uart.c
+++ b/hw/char/cmsdk-apb-uart.c
@@ -274,6 +274,7 @@ static void uart_write(void *opaque, hwaddr offset, 
uint64_t value,
          * is then reflected into the intstatus value by the update function).
          */
         s->state &= ~(value & (R_INTSTATUS_TXO_MASK | R_INTSTATUS_RXO_MASK));
+        s->intstatus &= ~(value & ~(R_INTSTATUS_TXO_MASK | 
R_INTSTATUS_RXO_MASK));
         cmsdk_apb_uart_update(s);
         break;
     case A_BAUDDIV:
-- 
2.16.2

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1760262

Title:
  cmsdk-apb-uart doesn't appear to clear interrupt flags

Status in QEMU:
  New

Bug description:
  I have been writing a small operating system and using QEMU emulating
  the mps2-an385 board for some of my testing.

  During development of the uart driver I observed some odd behaviour
  with the TX interrupt -- writing a '1' to bit 0 of the INTCLEAR
  register doesn't clear the TX interrupt flag, and the interrupt fires
  continuously.

  It's possible that I have an error somewhere in my code, but after
  inspecting the QEMU source it does appear to be a QEMU bug. I applied
  the following patch and it solved my issue:

  From 9875839c144fa60a3772f16ae44d32685f9328aa Mon Sep 17 00:00:00 2001
  From: Patrick Oppenlander <address@hidden>
  Date: Sat, 31 Mar 2018 15:10:28 +1100
  Subject: [PATCH] hw/char/cmsdk-apb-uart: fix clearing of interrupt flags

  ---
   hw/char/cmsdk-apb-uart.c | 1 +
   1 file changed, 1 insertion(+)

  diff --git a/hw/char/cmsdk-apb-uart.c b/hw/char/cmsdk-apb-uart.c
  index 1ad1e14295..64991bd9d7 100644
  --- a/hw/char/cmsdk-apb-uart.c
  +++ b/hw/char/cmsdk-apb-uart.c
  @@ -274,6 +274,7 @@ static void uart_write(void *opaque, hwaddr offset, 
uint64_t value,
            * is then reflected into the intstatus value by the update 
function).
            */
           s->state &= ~(value & (R_INTSTATUS_TXO_MASK | R_INTSTATUS_RXO_MASK));
  +        s->intstatus &= ~(value & ~(R_INTSTATUS_TXO_MASK | 
R_INTSTATUS_RXO_MASK));
           cmsdk_apb_uart_update(s);
           break;
       case A_BAUDDIV:
  -- 
  2.16.2

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