Re: [PATCH] hw/core: Introduce proxy-pic

[Bernhard Beschow]

Am 4. Januar 2023 22:22:01 UTC schrieb Mark Cave-Ayland 
<mark.cave-ayland@ilande.co.uk>:
>On 04/01/2023 19:53, Bernhard Beschow wrote:
>
>> Having a proxy PIC allows for ISA PICs to be created and wired up in
>> southbridges. This is especially useful for PIIX3 for two reasons:
>> First, the southbridge doesn't need to care about the virtualization
>> technology used (KVM, TCG, Xen) due to in-IRQs (where devices get
>> attached) and out-IRQs (which will trigger the IRQs of the respective
>> virtualization technology) are separated. Second, since the in-IRQs are
>> populated with fully initialized qemu_irq's, they can already be wired
>> up inside PIIX3.
>> 
>> Signed-off-by: Bernhard Beschow <shentey@gmail.com>
>> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
>> Message-Id: <20221022150508.26830-15-shentey@gmail.com>
>> ---
>> Changes since v4:
>> * Change license to GPL-2.0-or-later and use SPDX-License-Identifier
>> * Fix typo in commit message
>> ---
>>   include/hw/core/proxy-pic.h | 38 ++++++++++++++++++++++++++
>>   hw/core/proxy-pic.c         | 54 +++++++++++++++++++++++++++++++++++++
>>   MAINTAINERS                 |  2 ++
>>   hw/core/Kconfig             |  3 +++
>>   hw/core/meson.build         |  1 +
>>   5 files changed, 98 insertions(+)
>>   create mode 100644 include/hw/core/proxy-pic.h
>>   create mode 100644 hw/core/proxy-pic.c
>> 
>> diff --git a/include/hw/core/proxy-pic.h b/include/hw/core/proxy-pic.h
>> new file mode 100644
>> index 0000000000..32bc7936bd
>> --- /dev/null
>> +++ b/include/hw/core/proxy-pic.h
>> @@ -0,0 +1,38 @@
>> +/*
>> + * SPDX-License-Identifier: GPL-2.0-or-later
>> + *
>> + * Proxy interrupt controller device.
>> + *
>> + * Copyright (c) 2022 Bernhard Beschow <shentey@gmail.com>
>> + */
>> +
>> +#ifndef HW_PROXY_PIC_H
>> +#define HW_PROXY_PIC_H
>> +
>> +#include "hw/qdev-core.h"
>> +#include "qom/object.h"
>> +#include "hw/irq.h"
>> +
>> +#define TYPE_PROXY_PIC "proxy-pic"
>> +OBJECT_DECLARE_SIMPLE_TYPE(ProxyPICState, PROXY_PIC)
>> +
>> +#define MAX_PROXY_PIC_LINES 16
>> +
>> +/**
>> + * This is a simple device which has 16 pairs of GPIO input and output 
>> lines.
>> + * Any change on an input line is forwarded to the respective output.
>> + *
>> + * QEMU interface:
>> + *  + 16 unnamed GPIO inputs: the input lines
>> + *  + 16 unnamed GPIO outputs: the output lines
>> + */
>
>Re-reading this as a standalone patch, I can understand now why Phil was 
>asking about device properties etc. because aside from the commit message, it 
>isn't particularly clear that this is a workaround for QEMU's PIC devices and 
>accelerator implementations not (yet) supporting direct wiring with qdev 
>gpios. I would definitely argue that it is a special purpose and not a generic 
>device.
>
>I apologise that this is quite late in the review process, however given that 
>this wasn't immediately clear I do think it is worth making a few minor 
>changes. Perhaps something like:
>
>- Update the comment above in proxy_pic.h clarifying that this is only for 
>wiring up
>  ISA PICs (similar to the commit message) until gpios can be used

Will do.

>- Move the .c and .h files from hw/core/proxy-pic.c and 
>include/hw/core/proxy_pic.h
>  to hw/i386/proxy-pic.c and include/hw/i386/proxy_pic.h to provide a strong 
> hint
>  that the device is restricted to x86-only

The device gets used in PIIX4 as well, i.e. MIPS, too. I therefore think it is 
not x86 but rather PIC specific. I propose to move it back to hw/intc/i8259 
where it was implemented until v2: 
https://patchew.org/QEMU/20221022150508.26830-1-shentey@gmail.com/20221022150508.26830-15-shentey@gmail.com/
 . I can also rename the device back to isa-pic to make things more obvious.

What do you think?

Best regards,
Bernhard

>
>I think this makes it more obvious what the device is doing, and also prevent 
>its usage leaking into other places in the codebase. In fact in its current 
>form there is no need for device properties to configure the PIC lines, since 
>legacy x86 PICs always have 16 (ISA) IRQ lines.
>
>> +struct ProxyPICState {
>> +    /*< private >*/
>> +    struct DeviceState parent_obj;
>> +    /*< public >*/
>> +
>> +    qemu_irq in_irqs[MAX_PROXY_PIC_LINES];
>> +    qemu_irq out_irqs[MAX_PROXY_PIC_LINES];
>> +};
>> +
>> +#endif /* HW_PROXY_PIC_H */
>> diff --git a/hw/core/proxy-pic.c b/hw/core/proxy-pic.c
>> new file mode 100644
>> index 0000000000..40fd70b9e2
>> --- /dev/null
>> +++ b/hw/core/proxy-pic.c
>> @@ -0,0 +1,54 @@
>> +/*
>> + * SPDX-License-Identifier: GPL-2.0-or-later
>> + *
>> + * Proxy interrupt controller device.
>> + *
>> + * Copyright (c) 2022 Bernhard Beschow <shentey@gmail.com>
>> + */
>> +
>> +#include "qemu/osdep.h"
>> +#include "hw/core/proxy-pic.h"
>> +
>> +static void proxy_pic_set_irq(void *opaque, int irq, int level)
>> +{
>> +    ProxyPICState *s = opaque;
>> +
>> +    qemu_set_irq(s->out_irqs[irq], level);
>> +}
>> +
>> +static void proxy_pic_realize(DeviceState *dev, Error **errp)
>> +{
>> +    ProxyPICState *s = PROXY_PIC(dev);
>> +
>> +    qdev_init_gpio_in(DEVICE(s), proxy_pic_set_irq, MAX_PROXY_PIC_LINES);
>> +    qdev_init_gpio_out(DEVICE(s), s->out_irqs, MAX_PROXY_PIC_LINES);
>> +
>> +    for (int i = 0; i < MAX_PROXY_PIC_LINES; ++i) {
>> +        s->in_irqs[i] = qdev_get_gpio_in(DEVICE(s), i);
>> +    }
>> +}
>> +
>> +static void proxy_pic_class_init(ObjectClass *klass, void *data)
>> +{
>> +    DeviceClass *dc = DEVICE_CLASS(klass);
>> +
>> +    /* No state to reset or migrate */
>> +    dc->realize = proxy_pic_realize;
>> +
>> +    /* Reason: Needs to be wired up to work */
>> +    dc->user_creatable = false;
>> +}
>> +
>> +static const TypeInfo proxy_pic_info = {
>> +    .name          = TYPE_PROXY_PIC,
>> +    .parent        = TYPE_DEVICE,
>> +    .instance_size = sizeof(ProxyPICState),
>> +    .class_init = proxy_pic_class_init,
>> +};
>> +
>> +static void split_irq_register_types(void)
>> +{
>> +    type_register_static(&proxy_pic_info);
>> +}
>> +
>> +type_init(split_irq_register_types)
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 7a40d4d865..295a76bfbd 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -1674,6 +1674,7 @@ S: Supported
>>   F: hw/char/debugcon.c
>>   F: hw/char/parallel*
>>   F: hw/char/serial*
>> +F: hw/core/proxy-pic.c
>>   F: hw/dma/i8257*
>>   F: hw/i2c/pm_smbus.c
>>   F: hw/input/pckbd.c
>> @@ -1690,6 +1691,7 @@ F: hw/watchdog/wdt_ib700.c
>>   F: hw/watchdog/wdt_i6300esb.c
>>   F: include/hw/display/vga.h
>>   F: include/hw/char/parallel.h
>> +F: include/hw/core/proxy-pic.h
>>   F: include/hw/dma/i8257.h
>>   F: include/hw/i2c/pm_smbus.h
>>   F: include/hw/input/i8042.h
>> diff --git a/hw/core/Kconfig b/hw/core/Kconfig
>> index 9397503656..a7224f4ca0 100644
>> --- a/hw/core/Kconfig
>> +++ b/hw/core/Kconfig
>> @@ -22,6 +22,9 @@ config OR_IRQ
>>   config PLATFORM_BUS
>>       bool
>>   +config PROXY_PIC
>> +    bool
>> +
>>   config REGISTER
>>       bool
>>   diff --git a/hw/core/meson.build b/hw/core/meson.build
>> index 7a4d02b6c0..e86aef6ec3 100644
>> --- a/hw/core/meson.build
>> +++ b/hw/core/meson.build
>> @@ -30,6 +30,7 @@ softmmu_ss.add(when: ['CONFIG_GUEST_LOADER', fdt], 
>> if_true: files('guest-loader.
>>   softmmu_ss.add(when: 'CONFIG_OR_IRQ', if_true: files('or-irq.c'))
>>   softmmu_ss.add(when: 'CONFIG_PLATFORM_BUS', if_true: 
>> files('platform-bus.c'))
>>   softmmu_ss.add(when: 'CONFIG_PTIMER', if_true: files('ptimer.c'))
>> +softmmu_ss.add(when: 'CONFIG_PROXY_PIC', if_true: files('proxy-pic.c'))
>>   softmmu_ss.add(when: 'CONFIG_REGISTER', if_true: files('register.c'))
>>   softmmu_ss.add(when: 'CONFIG_SPLIT_IRQ', if_true: files('split-irq.c'))
>>   softmmu_ss.add(when: 'CONFIG_XILINX_AXI', if_true: files('stream.c'))
>
>
>ATB,
>
>Mark.