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Re: [PATCH 4/7] ppc/pnv: Simplify pnv_bmc_create()

From: Cédric Le Goater
Subject: Re: [PATCH 4/7] ppc/pnv: Simplify pnv_bmc_create()
Date: Fri, 29 Jan 2021 09:39:14 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

On 1/28/21 11:40 PM, David Gibson wrote:
> On Thu, Jan 28, 2021 at 08:46:01AM +0100, Cédric Le Goater wrote:
>> On 1/28/21 1:46 AM, Joel Stanley wrote:
>>> On Tue, 26 Jan 2021 at 17:14, Cédric Le Goater <clg@kaod.org> wrote:
>>>> and reuse pnv_bmc_set_pnor() to share the setting of the PNOR.
>>>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
>>>> ---
>>>>  hw/ppc/pnv_bmc.c | 7 +------
>>>>  1 file changed, 1 insertion(+), 6 deletions(-)
>>>> diff --git a/hw/ppc/pnv_bmc.c b/hw/ppc/pnv_bmc.c
>>>> index 67ebb16c4d5f..86d16b493539 100644
>>>> --- a/hw/ppc/pnv_bmc.c
>>>> +++ b/hw/ppc/pnv_bmc.c
>>>> @@ -260,13 +260,8 @@ IPMIBmc *pnv_bmc_create(PnvPnor *pnor)
>>>>      Object *obj;
>>>>      obj = object_new(TYPE_IPMI_BMC_SIMULATOR);
>>>> -    object_ref(OBJECT(pnor));
>>>> -    object_property_add_const_link(obj, "pnor", OBJECT(pnor));
>>> I assume it's ok to move the link set to after the realise of the BMC 
>>> object?
>> When 2 objects need to be linked, one has to be realized first. 
>> I suppose this is why it is allowed but I am not expert in that area. 
>> Greg  ?
>> That was the case already when defining a "ipmi-bmc-sim" device on the 
>> command line.
> Well, the other thing here is that the IPMI_BMC_SIMULATOR isn't a
> POWER specific object, and doesn't actually know anything about pnor,
> so it never looks at that property.  Do we even need it?

It does through hiomap_cmd() which handles HIOMAP commands related 
to the PNOR. The link was introduced to remove a reference to the 
global machine (qdev_get_machine()). The PNOR device is instantiated 
at the machine level but conceptually, this is incorrect. 

The PNOR is a device controlled by the BMC and accessed by the host 
through a mapping on the LPC FW address space. It used to be controlled 
from the host also, through the iLPC2AHB device and mboxes, but these 
"doors" were closed sometime ago.

I am thinking of moving the PNOR at the BMC level. It won't change 
the default device settings but '-nodefaults' will result in no PNOR, 
same impact if the BMC device is an external one, but that's a more 
complex matter. We would need a way to model memory operations on a 
LPC bus shared by two QEMU machines.

We are doing something similar with the Aspeed iBT device but it's
very specific to this device. I hope the QEMU multi-process patchset
offers some framework on which we can build upon.


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