Re: [Qemu-devel] [Qemu-ppc] [PATCH v2 1/2] spapr: Add support for hwrng when available

[Thomas Huth <thuth@redhat.com>]

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On 09/09/15 23:10, Thomas Huth wrote:
> On 08/09/15 07:15, David Gibson wrote:
...
>> At this point rather than just implementing them as discrete machine
>> options, I suspect it will be more maintainable to split out the
>> h-random implementation as a pseudo-device with its own qdev and so
>> forth.  We already do similarly for the RTAS time of day functions
>> (spapr-rtc).
> 
> I gave that I try, but it does not work as expected. To be able to
> specify the options, I'd need to instantiate this device with the
> "-device" option, right? Something like:
> 
> 	-device spapr-rng,backend=rng0,usekvm=0
> 
> Now this does not work when I use TYPE_SYS_BUS_DEVICE as parent class
> like it is done for spapr-rtc, since the user apparently can not plug
> device to this bus on machine spapr (you can also not plug an spapr-rtc
> device this way!).
> 
> The spapr-vlan, spapr-vty, etc. devices are TYPE_VIO_SPAPR_DEVICE, so I
> also tried that instead, but then the rng device suddenly shows up under
> /vdevice in the device tree - that's also not what we want, I guess.

I did some more tests, and I think I can get this working with one small
modification to spapr_vio.c:

diff --git a/hw/ppc/spapr_vio.c b/hw/ppc/spapr_vio.c
index c51eb8e..8e7f6b4 100644
--- a/hw/ppc/spapr_vio.c
+++ b/hw/ppc/spapr_vio.c
@@ -99,6 +99,14 @@ static int vio_make_devnode(VIOsPAPRDevice *dev,
     int vdevice_off, node_off, ret;
     char *dt_name;

+    if (!pc->dt_name) {
+        ret = 0;
+        if (pc->devnode) {
+            ret = (pc->devnode)(dev, fdt, -1);
+        }
+        return ret;
+    }
+
     vdevice_off = fdt_path_offset(fdt, "/vdevice");
     if (vdevice_off < 0) {
         return vdevice_off;

i.e. when the dt_name has not been set, the device won't be added to the
/vdevice device tree node. If that's acceptable, I'll continue with this
approach.

 Thomas



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