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

[Peter Maydell]

Thanks for the bug report; I've submitted this patch (which is similar to but 
not quite the same as your fix):
https://patchwork.ozlabs.org/patch/896715/

Hopefully this will get into 2.12, but we're quite close to release now
so it will depend on whether we need to spin an extra release candidate
for some other reason.


** Changed in: qemu
       Status: New => In Progress

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

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

Status in QEMU:
  In Progress

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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