August 2021 - Stratos-dev - op-lists.linaro.org

[PATCH V5 0/2] gpio: Add virtio based driver

by Viresh Kumar

Hello, This adds Virtio GPIO driver based on the proposed specification [1]. The specification for basic GPIO operations is already reviewed by Linus and Arnd, while the IRQ stuff is still under discussion and not finalized. I am sharing the code, so everyone gets more clarity on how it will work eventually in Linux. I have tested this patchset with Qemu guest with help of the libgpiod utility. I have also tested basic handling of interrupts on the guest side. It works as expected. The host side virtio-backend isn't ready yet and my tests only tested the flow control between guest and host, but didn't play with real GPIO pins. That will be done once I have a working backend in place (WIP). V4->V5: - Use ____cacheline_aligned for buffers. - Proper locking in place, which avoids the use of work-item for processing interrupts. - Separate callbacks for enable/disable of irqs. - The irq is disabled at the host only for enable/disable now, instead of mask/unmask. - mask/unmask only control the queuing of buffers now. - Use handle_level_irq() instead of handle_fasteoi_irq(). - Other minor changes. V3->V4: - Lots of changes, as the specification changed too much. Better forget everything we have done until now :) -- Viresh [1] https://lists.oasis-open.org/archives/virtio-dev/202107/msg00232.html Viresh Kumar (2): gpio: Add virtio-gpio driver gpio: virtio: Add IRQ support MAINTAINERS | 7 + drivers/gpio/Kconfig | 10 + drivers/gpio/Makefile | 1 + drivers/gpio/gpio-virtio.c | 668 +++++++++++++++++++++++++++++++ include/uapi/linux/virtio_gpio.h | 72 ++++ 5 files changed, 758 insertions(+) create mode 100644 drivers/gpio/gpio-virtio.c create mode 100644 include/uapi/linux/virtio_gpio.h -- 2.31.1.272.g89b43f80a514

4 years

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Re: [Stratos-dev] virtio-proxy approach for hypervisor-agnostic backend

by Alex Bennée

AKASHI Takahiro via Stratos-dev <stratos-dev(a)op-lists.linaro.org> writes: > Hi All, > > # Some of you might have received a similar message, the purpose > # is the same, but for wider audience. > > I have been thinking of some idea of creating hypervisor-agnostic > framework which will enable us to implement virtio device (backend) > VMs on whatever the underlying hypervisor is. The aim is to > create VMs as bare-metal applications using a small number of > "common" vm services. I name this framework "virtio proxy"[1]. > (You can think it as my solution proposal against the topic which > Alex raised a concern on yesterday.) > > Now it is the time that we have to decide whether this approach > can appeal to you and meet your requirements, and so if it is worth > my continuing this study in the *next development cycle* which will > start in September (or October). > > 1) Please give me your insights/feedback against my proposal. > If we see no positive feedback or interest in the next two weeks or so, > especially, from member company engineers, this study will be > automatically *cancelled*. > > 2) If there is any interest seen, I will like to set up a dedicated > Stratos call meeting in two weeks timeframe to discuss more. > What is the best time slot for you? > As I live in Japan, UTC-6, 7, or 8 (or even earlier) would be the best, > but I would like to hear from member company engineers in West coast of > USA, the timeslot is quite flexible. > > > Here is my draft proposal: > [1] > https://docs.google.com/presentation/d/1jAOKbQpv44Rje74OI4pNKXlsCfRCQf547lH… I think it would be useful to discuss this at the next Stratos meeting at the beginning of September as we discuss the ways forward for the next cycle of development. More broadly now we have a bunch of backends implemented it's time to start considering the various approaches to hypervisor agnosticism. Mike, Can we shift the Sept meeting to a morning slot to better align with JST? > > Thanks, > -Takahiro Akashi -- Alex Bennée

4 years

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Re: [Stratos-dev] [PATCH V4 2/2] gpio: virtio: Add IRQ support

by Arnd Bergmann

On Mon, Aug 9, 2021 at 12:47 PM Viresh Kumar via Stratos-dev <stratos-dev(a)op-lists.linaro.org> wrote: > > On 09-08-21, 09:55, Arnd Bergmann wrote: > > Ah, right. There is already a flag that gets checked by the caller. > > > > It does feel odd to have an empty 'irq_mask' callback though, so > > maybe there is still something missing, just not what I thought. > > > > It's probably the result of calling handle_level_irq(), which as you > > said is closer to what we want, but is not exactly what we need for > > this protocol. > > Okay, I have tried to take care of locking as well now and used local > flags only to make sure I can depend on them to get the locking > working properly. Lets see what's broken in this now :) I don't see anything wrong with this version, but let's see what Marc thinks. I expect that he can still poke some holes in it, or at least find some simplifications. I was slightly surprised at the relation between the disabled and masked states, where 'disable' always implies 'mask' and 'enable' always implies 'unmask', but I don't actually know how those two are actually defined in the irqchip code in Linux, so I assume you did this correctly. Arnd

4 years, 1 month

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Re: [Stratos-dev] [PATCH V4 2/2] gpio: virtio: Add IRQ support

by Arnd Bergmann

On Fri, Aug 6, 2021 at 9:44 AM Viresh Kumar via Stratos-dev <stratos-dev(a)op-lists.linaro.org> wrote: > > On 05-08-21, 15:10, Arnd Bergmann wrote: > > I hope this can still be simplified by working out better which state > > transitions are needed exactly. In particular, I would expect that we > > can get away with not sending a VIRTIO_GPIO_MSG_IRQ_TYPE > > for 'mask' state changes at all, but use that only for forcing 'enabled' > > state changes. > > Something like this ? > static void virtio_gpio_irq_mask(struct irq_data *d) > { > /* Nothing to do here */ > } You'd have to do /something/ here I think, if only setting the flag that we don't want to deliver the next interrupt. > static void virtio_gpio_irq_unmask(struct irq_data *d) > { > struct gpio_chip *gc = irq_data_get_irq_chip_data(d); > struct virtio_gpio *vgpio = gpiochip_get_data(gc); > > /* Queue the buffer unconditionally on unmask */ > virtio_gpio_irq_prepare(vgpio, d->hwirq); > } And check the flag here to not requeue it if it's masked. Now, there is already a flag in the irq descriptor, so rather than having double accounting, the easy way may be to just use irqd_irq_masked()/irq_state_set_masked(), or have the irq core take care of this. Arnd

4 years, 1 month

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[PATCH V8 0/2] virtio: Add specification for virtio-gpio

by Viresh Kumar

Hello, This patchset adds virtio specification for GPIO devices. It supports basic GPIO line operations, along with optional interrupts on them (in a separate patch). This is an *alternative implementation* of the virtio-gpio specification, a different version of it was earlier posted by Enrico [1]. I took back V4 of the specification I posted earlier (on June 17th), to allow Enrico to come up with something that is robust and works for everyone (as he started this thing last year), but it didn't go as expected. I couldn't see any of my review comments being incorporated (or any intentions of them getting in ever) in the three versions Enrico posted until now. This patchset is already reviewed by Linus (GPIO Maintainer) and Arnd. Key differences from Enrico's approach [1]: - config structure is rearranged to remove everything apart from number of gpios and size of the gpio_names_field. - Request/free is merged with set-direction itself. - Interrupt implementation handled with feature bit 0. Either the interrupts are fully supported or not at all. - All non-interrupt traffic happens on a single virtqueue, requestq. Interrupt traffic goes over eventq. - Doesn't add any ordering restrictions on the device for different GPIO lines, it can respond earlier to the second request, while still processing the first one. Version history of the my changes: V7 -> V8: - Use fixed-length struct virtio_gpio_response for all requests and define a separate structure for get-names. - Explicitly write the expected values of direction in the get/set-direction tables. - Better/detailed interrupt handling information, based on fast-eoi mechanism now, where the driver notifies the device only once after the interrupt is handled. - Added reviewed-by tags collected so far. V6 -> V7: - Drop Activate/Deactivate requests and merge them with set-direction one. - Dropped separate calls to set direction to input or output (with a value), with a single call to set-direction (input, output, or none). Note that the driver needs to call set-value before calling set-direction-out now. - Allow multiple messages for a GPIO line to be sent together, they must be processed in order though. - The gpio-line names aren't required to be set for all the lines now, it is optional and can be present only for a subset of lines. Provided example as well. - Merge irq-set/mask/unmask to a single set-irq-type message. - We have only 6 message types now instead of 11 in v6. - Mentioned about non-atomic nature of the these messages in commit log for patch 1/2. - Improved spec content overall. V5 -> V6: - All non-interrupt traffic happens on a single virtqueue, requestq. Interrupt traffic goes over eventq now. - Many fields dropped from the config structure. - Separate message type to get gpio-names, added more description about how the names should be. - Much clearer message flows, both non-irq messages and irq-messages. - Parallelism supported for all type of messages, for different GPIO pins. - All references to POSIX errors dropped, just reply pass or fail. - request/free renamed to activate/deactivate, as that's what we will end up doing there, activate or deactivate a GPIO line. - General purpose IO as I/O or Input/Output instead. - Hopefully I didn't miss any review comments. V4 -> V5: - Split into two patches, irq stuff in patch 2. - Use separate virtqueue for sending data from device/driver. - Allow parallel processing of requests for different GPIOs, only one request at a time for the same GPIO line. - Same goes for interrupt side, only one interrupt request per GPIO line. - Improved formatting in general. - Add new sections explaining message flow sequence. V3 -> V4: - The GPIO line names must be unique within a device. - The gpio_names[0] field is dropped and gpio_names_offset field is added in place of the 2 bytes of padding. - New interrupts must not be initiated by the device, without a response for the previous one. V2 -> V3: - Unused char in name string should be marked 0 now. - s/host/device/ and s/guest/driver/ - Added a new feature for IRQ mode, VIRTIO_GPIO_F_IRQ. - A new feature should be added for Version information if required later on. V1 -> V2: - gpio_names_size is 32 bit. - gpio field is 16 bit. - padding added 16 bit. - Added packed attribute to few structures - Add the missing 'type' field to the request - Dropped to _nodata request/responses to simplify a bit, updated related text. -- Viresh [1] https://lists.oasis-open.org/archives/virtio-dev/202106/msg00030.html Viresh Kumar (2): virtio-gpio: Add the device specification virtio-gpio: Add support for interrupts conformance.tex | 30 ++- content.tex | 1 + virtio-gpio.tex | 578 ++++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 605 insertions(+), 4 deletions(-) create mode 100644 virtio-gpio.tex -- 2.31.1.272.g89b43f80a514

4 years, 1 month

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Re: [Stratos-dev] [PATCH V4 2/2] gpio: virtio: Add IRQ support

by Arnd Bergmann

On Thu, Aug 5, 2021 at 1:26 PM Viresh Kumar via Stratos-dev <stratos-dev(a)op-lists.linaro.org> wrote: > > On 03-08-21, 17:01, Arnd Bergmann wrote: > > As far as I can tell, the update_irq_type() message would lead to the > > interrupt getting delivered when it was armed and is now getting disabled, > > but I don't see why we would call update_irq_type() as a result of the > > eventq notification. > > Based on discussion we had today (offline), I changed the design a bit > and used handle_level_irq() instead, as it provides consistent calls > to mask/unmask(), which simplified the whole thing a bit. The new flow looks much nicer to me, without the workqueue, and doing the requeue directly in the unmask() operation. I don't quite understand the purpose of the type_pending and mask_pending flags yet, can you explain what they actually do? Also, I have no idea about whether using the handle_level_irq() function is actually correct here. I suppose if necessary, the driver could provide its own irq.handler callback in place of that. > Also I have broken the rule from specs, maybe we should update spec > with that, where the specs said that the buffer must not be queued > before enabling the interrupt. I just queue the buffer unconditionally > now from unmask(). > > I am not sure but there may be some race around the "queued" flag and > I wonder if we can land in a scenario where the buffer is left > un-queued somehow, while an interrupt is enabled. Can that be integrated with the "masked" state now? It looks like the two flags are always opposites now. Arnd

4 years, 1 month

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[PATCH V4 0/2] gpio: Add virtio based driver

by Viresh Kumar

Hello, This adds Virtio GPIO driver based on the proposed specification [1]. The specification for basic GPIO operations is already reviewed by Linus and Arnd, while the IRQ stuff is still under discussion and not finalized. I am sharing the code, so everyone gets more clarity on how it will work eventually in Linux. I have tested this patchset with Qemu guest with help of the libgpiod utility. I have also tested basic handling of interrupts on the guest side. It works as expected. The host side virtio-backend isn't ready yet and my tests only tested the flow control between guest and host, but didn't play with real GPIO pins. That will be done once I have a working backend in place (WIP). V3->V4: - Lots of changes, as the specification changed too much. Better forget everything we have done until now :) -- Viresh [1] https://lists.oasis-open.org/archives/virtio-dev/202107/msg00232.html Viresh Kumar (2): gpio: Add virtio-gpio driver gpio: virtio: Add IRQ support MAINTAINERS | 7 + drivers/gpio/Kconfig | 10 + drivers/gpio/Makefile | 1 + drivers/gpio/gpio-virtio.c | 648 +++++++++++++++++++++++++++++++ include/uapi/linux/virtio_gpio.h | 72 ++++ 5 files changed, 738 insertions(+) create mode 100644 drivers/gpio/gpio-virtio.c create mode 100644 include/uapi/linux/virtio_gpio.h -- 2.31.1.272.g89b43f80a514

4 years, 1 month

2
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virtio-proxy approach for hypervisor-agnostic backend

by AKASHI Takahiro

Hi All, # Some of you might have received a similar message, the purpose # is the same, but for wider audience. I have been thinking of some idea of creating hypervisor-agnostic framework which will enable us to implement virtio device (backend) VMs on whatever the underlying hypervisor is. The aim is to create VMs as bare-metal applications using a small number of "common" vm services. I name this framework "virtio proxy"[1]. (You can think it as my solution proposal against the topic which Alex raised a concern on yesterday.) Now it is the time that we have to decide whether this approach can appeal to you and meet your requirements, and so if it is worth my continuing this study in the *next development cycle* which will start in September (or October). 1) Please give me your insights/feedback against my proposal. If we see no positive feedback or interest in the next two weeks or so, especially, from member company engineers, this study will be automatically *cancelled*. 2) If there is any interest seen, I will like to set up a dedicated Stratos call meeting in two weeks timeframe to discuss more. What is the best time slot for you? As I live in Japan, UTC-6, 7, or 8 (or even earlier) would be the best, but I would like to hear from member company engineers in West coast of USA, the timeslot is quite flexible. Here is my draft proposal: [1] https://docs.google.com/presentation/d/1jAOKbQpv44Rje74OI4pNKXlsCfRCQf547lH… Thanks, -Takahiro Akashi

4 years, 1 month

1
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Stratos-dev August 2021