diff mbox series

[v2] hw/block/fdc-sysbus: Always mark sysbus floppy controllers as not having DMA

Message ID 20220505101842.2757905-1-peter.maydell@linaro.org
State Accepted
Headers show
Series [v2] hw/block/fdc-sysbus: Always mark sysbus floppy controllers as not having DMA | expand

Commit Message

Peter Maydell May 5, 2022, 10:18 a.m. UTC 
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(-)

Comments

Markus Armbruster May 5, 2022, 11:52 a.m. UTC | #1 
Peter Maydell <peter.maydell@linaro.org> writes:

> 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.

Worth a

  Fixes: 1430759ec3e4cb92da224d739c914a0e8d78d786

tag?

>
> 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>
Philippe Mathieu-Daudé May 30, 2022, 2:15 p.m. UTC | #2 
On 5/5/22 12:18, Peter Maydell wrote:
> 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(-)

Queued to mips-next, thanks.
diff mbox series

Patch

diff --git a/include/hw/block/fdc.h b/include/hw/block/fdc.h
index 1ecca7cac7f..35248c08379 100644
--- a/include/hw/block/fdc.h
+++ b/include/hw/block/fdc.h
@@ -10,8 +10,7 @@ 
 #define TYPE_ISA_FDC "isa-fdc"
 
 void isa_fdc_init_drives(ISADevice *fdc, DriveInfo **fds);
-void fdctrl_init_sysbus(qemu_irq irq, int dma_chann,
-                        hwaddr mmio_base, DriveInfo **fds);
+void fdctrl_init_sysbus(qemu_irq irq, hwaddr mmio_base, DriveInfo **fds);
 void sun4m_fdctrl_init(qemu_irq irq, hwaddr io_base,
                        DriveInfo **fds, qemu_irq *fdc_tc);
 
diff --git a/hw/block/fdc-sysbus.c b/hw/block/fdc-sysbus.c
index 57fc8773f12..86ea51d0034 100644
--- a/hw/block/fdc-sysbus.c
+++ b/hw/block/fdc-sysbus.c
@@ -94,18 +94,14 @@  static void fdctrl_handle_tc(void *opaque, int irq, int level)
     trace_fdctrl_tc_pulse(level);
 }
 
-void fdctrl_init_sysbus(qemu_irq irq, int dma_chann,
-                        hwaddr mmio_base, DriveInfo **fds)
+void fdctrl_init_sysbus(qemu_irq irq, hwaddr mmio_base, DriveInfo **fds)
 {
-    FDCtrl *fdctrl;
     DeviceState *dev;
     SysBusDevice *sbd;
     FDCtrlSysBus *sys;
 
     dev = qdev_new("sysbus-fdc");
     sys = SYSBUS_FDC(dev);
-    fdctrl = &sys->state;
-    fdctrl->dma_chann = dma_chann; /* FIXME */
     sbd = SYS_BUS_DEVICE(dev);
     sysbus_realize_and_unref(sbd, &error_fatal);
     sysbus_connect_irq(sbd, 0, irq);
@@ -138,6 +134,16 @@  static void sysbus_fdc_common_instance_init(Object *obj)
     FDCtrlSysBus *sys = SYSBUS_FDC(obj);
     FDCtrl *fdctrl = &sys->state;
 
+    /*
+     * DMA is not currently supported for sysbus floppy controllers.
+     * If we wanted to add support then probably the best approach is
+     * to have a QOM link property 'dma-controller' which the board
+     * code can set to an instance of IsaDmaClass, and an integer
+     * property 'dma-channel', so that we can set fdctrl->dma and
+     * fdctrl->dma_chann accordingly.
+     */
+    fdctrl->dma_chann = -1;
+
     qdev_set_legacy_instance_id(dev, 0 /* io */, 2); /* FIXME */
 
     memory_region_init_io(&fdctrl->iomem, obj,
diff --git a/hw/mips/jazz.c b/hw/mips/jazz.c
index 6598d7dddd5..96dc6ab32dd 100644
--- a/hw/mips/jazz.c
+++ b/hw/mips/jazz.c
@@ -353,7 +353,7 @@  static void mips_jazz_init(MachineState *machine,
         fds[n] = drive_get(IF_FLOPPY, 0, n);
     }
     /* FIXME: we should enable DMA with a custom IsaDma device */
-    fdctrl_init_sysbus(qdev_get_gpio_in(rc4030, 1), -1, 0x80003000, fds);
+    fdctrl_init_sysbus(qdev_get_gpio_in(rc4030, 1), 0x80003000, fds);
 
     /* Real time clock */
     mc146818_rtc_init(isa_bus, 1980, NULL);