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From: | Damien Hedde |
Subject: | Re: [RFC PATCH v5 0/3] Sysbus device generic QAPI plug support |
Date: | Wed, 25 May 2022 11:51:31 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 |
On 5/24/22 19:44, Mark Cave-Ayland wrote:
On 24/05/2022 14:48, Damien Hedde wrote:Hi all, This series is about enabling to plug sysbus devices with device_add QAPI command. I've put RFC because, there are several options and I would like to know if you think the current version is ok to be added in qemu. Right now only a few sysbus device can be plugged using "-device" CLI option and a custom plugging mechanism. A machine defines a list of allowed/supported sysbus devices and provides some code to handle the plug. For example, it sets up the memory map and irq connections. In order to configure a machine from scratch with qapi, we want to cold plug sysbus devices to the _none_ machine with qapi commands without requiring the machine to provide some specific per-device support. There are mostly 2 options (option 1 is in these patches). Note that in any case this only applies to "user-creatable" device. + Option 1: Use the current plug mechanism by allowing any sysbus device, without adding handle code in the machine. + Option 2: Add a boolean flag in the machine to allow to plug any sysbus device. We can additionally differentiate the sysbus devices requiring the legacy plug mechanism (with a flag, for example) and the others. The setup of the memory map and irq connections is not related to the option choice above. We planned to rely on qapi commands to do these operations. A new _sysbus-mmio-map_ command is proposed in this series to setup the mapping. Irqs can already be connected using the _qom-set_ command. Alternatively we could probably add parameters/properties to device_add to handle the memory map, but it looks more complicated to achieve. Based-on: <20220519153402.41540-1-damien.hedde@greensocs.com> ( QAPI support for device cold-plug ) Note that it does not stricly require this to be merged, but this series does not make much sense without the ability to cold plug with device_add first. Thanks for your feedback, -- Damien Damien Hedde (3): none-machine: allow cold plugging sysbus devices softmmu/memory: add memory_region_try_add_subregion function add sysbus-mmio-map qapi command qapi/qdev.json | 31 ++++++++++++++++++++++++++ include/exec/memory.h | 22 +++++++++++++++++++ hw/core/null-machine.c | 4 ++++ hw/core/sysbus.c | 49 ++++++++++++++++++++++++++++++++++++++++++ softmmu/memory.c | 26 ++++++++++++++-------- 5 files changed, 123 insertions(+), 9 deletions(-)Sorry for coming late into this series, however one of the things I've been thinking about a lot recently is that with the advent of QOM and qdev, is there really any distinction between TYPE_DEVICE and TYPE_SYS_BUS_DEVICE anymore, and whether it makes sense to keep TYPE_SYS_BUS_DEVICE long term.
On QAPI/CLI level there is a huge difference since TYPE_SYS_BUS_DEVICE is the only subtype of TYPE_DEVICE which is subject to special treatment. It prevents to plug a sysbus device which has not be allowed by code and that's what I want to get rid of (or workaround by allowing all of them).
No objection to the concept of being able to plug devices into the none machine, but I'm wondering if the "sysbus-mmio-map" QAPI command should be a generic "device-map" instead so that the concept of SYS_BUS_DEVICE doesn't leak into QAPI.
It is possible to change this command to a more generic command if people feel better with it. Instead of providing a mmio index we just need to provide an argument to identify the memory region in the device (by it's name/path maybe ?).
Can you give a bit more detail as to the sequence of QMP transactions that would be used to map a SYS_BUS_DEVICE with this series applied? I'm particularly interested to understand how SYS_BUS_DEVICEs are identified, and how their memory regions and gpios are enumerated by the client to enable it to generate the final "sysbus-mmio-map" and "qom-set" commands.
Here's a typical example of commands to create and connect an uart (here "plic" is the id of the interrupt controller created before):
> device_add driver=ibex-uart id=uart chardev=serial0 > sysbus-mmio-map device=uart addr=1073741824 > qom-set path=uart property=sysbus-irq[0] value=plic/unnamed-gpio-in[1] > qom-set path=uart property=sysbus-irq[1] value=plic/unnamed-gpio-in[2] > qom-set path=uart property=sysbus-irq[2] value=plic/unnamed-gpio-in[3] > qom-set path=uart property=sysbus-irq[3] value=plic/unnamed-gpio-in[4]This comes from one of my example here (it needs more patches than this series): https://github.com/GreenSocs/qemu-qmp-machines/blob/master/riscv-opentitan/machine.qmp
I'm note sure what you mean by identification and enumeration. I do not do any introspection and rely on knowing which mmio or irq index corresponds to what. The "id" in `device_add` allows to reference the device in following commands.
Thanks, -- Damien
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