The sysbus floppy controllers (devices sysbus-fdc and sun-fdtwo)
don't support DMA. The core floppy controller code expects this to
be indicated by setting FDCtrl::dma_chann to -1. This used to be
done in the device instance_init functions sysbus_fdc_initfn() and
sun4m_fdc_initfn(), but in commit 1430759ec3e we refactored this code
and accidentally lost the setting of dma_chann.
For sysbus-fdc this has no ill effects because we were redundantly
also setting dma_chann in fdctrl_init_sysbus(), but for sun-fdtwo
this means that guests which try to enable DMA on the floppy
controller will cause QEMU to crash because FDCtrl::dma is NULL.
Set dma_chann to -1 in the common instance init, and remove the
redundant code in fdctrl_init_sysbus() that is also setting it.
There is a six-year-old FIXME comment in the jazz board code to the
effect that in theory it should support doing DMA via a custom DMA
controller. If anybody ever chooses to fix that they can do it by
adding support for setting both FDCtrl::dma_chann and FDCtrl::dma.
(A QOM link property 'dma-controller' on the sysbus device which can
be set to an instance of IsaDmaClass is probably the way to go.)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/958
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
Changes v1->v2: remove now-unused 'fdctrl' local variable
from fdctrl_init_sysbus()
---
include/hw/block/fdc.h | 3 +--
hw/block/fdc-sysbus.c | 16 +++++++++++-----
hw/mips/jazz.c | 2 +-
3 files changed, 13 insertions(+), 8 deletions(-)