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Re: [Qemu-devel] [PATCH v2 5/9] hw/block/pflash_cfi01: Add the DeviceRes

From: Laszlo Ersek
Subject: Re: [Qemu-devel] [PATCH v2 5/9] hw/block/pflash_cfi01: Add the DeviceReset() handler
Date: Tue, 2 Jul 2019 16:32:36 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 07/02/19 11:37, Philippe Mathieu-Daudé wrote:
> On 7/2/19 11:23 AM, Peter Maydell wrote:
>> On Tue, 2 Jul 2019 at 04:16, John Snow <address@hidden> wrote:
>>> Does reset always get called as part of realize, really?
>>> Or are we just trusting that the device is probably going to get reset
>>> by the guest during bringup?
>> Reset is not called "as part of realize", but it is guaranteed
>> to be called after realize and before we try to run the guest,
>> as long as the device is in the qbus tree. Things are in the
>> qbus tree if either:
>>  * they're plugged into something already in the tree (eg
>>    pci devices, scsi disks)
>>  * they're a sysbus device (which is automatically plugged into
>>    the 'main system bus' which is effectively the root of the
>>    qbus tree)
>> In this case TYPE_PFLASH_CFI01 is a subclass of TYPE_SYS_BUS_DEVICE,
>> so it will always be reset as part of system reset.
>> (the main things which don't get automatically reset are direct
>> subclasses of TYPE_DEVICE, notably CPU objects.)
> Thanks for the clarification!
> I will update the commit description paraphrasing Peter:
>   The TYPE_DEVICE interface provides a DeviceReset handler.
>   This pflash device is a subclass of TYPE_SYS_BUS_DEVICE (which
>   is a subclass of TYPE_DEVICE).
>   SYS_BUS devices are automatically plugged into the 'main system
>   bus', which is the root of the qbus tree.
>   Devices in the qbus tree are guaranteed to have their reset()
>   handler called after realize() and before we try to run the guest.
>   To avoid incoherent states when the machine resets (see but report
>   below), factor out the reset code into pflash_cfi01_system_reset,
>   and register the method as a device reset callback.
> John, Laszlo, is that OK with you?

works for me, sure.


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