Re: [Qemu-devel] Modeling a device controlled by combination of GPIO and UART

[Martin Schroeder]

Thanks Peter.

I have set it up such that master device has qemu_irq array which it
initializes using qdev_init_gpio_out with number of gpio lines going
out and slave device calls qdev_init_gpio_in with a callback that
should be called when irq is raised. Then I connect them together at
higher level using qdev_connect_gpio_out as you said. Then master
calls qemu_set_irq with 1 or 0 depending on whether the gpio is high
or low.

This works, but not as I would expect. The handler that I supply to
the init_gpio_in is only being called very infrequently - perhaps once
every 50 toggles on the gpio pin. I need to make sure that it gets
called every time master device calls qemu_set_irq.

What's the mechanism behind this behavior and how can I deliver gpio
change to the slave?
On Tue, Aug 21, 2018 at 3:57 PM Peter Maydell <address@hidden> wrote:
>
> On 21 August 2018 at 14:29, Martin Schroeder via Qemu-devel
> <address@hidden> wrote:
> > I'd like to add a virtual device that is controlled by a couple of
> > GPIO pins on my controller (cortex-m4) and a serial port. I suppose I
> > can derive it from SSISlaveClass to make the new device a serial
> > slave.
> >
> > But how do I connect GPIOs?
> >
> > I want the slave device to be notified when guest firmware toggles a
> > gpio pin through the gpio driver which is an mmio device mapped into
> > the gpio memory area. So the GPIO driver currently keeps the state of
> > the pins internal to the driver. What I would like to do is somehow,
> > without requiring that the GPIO driver knows about the connected slave
> > device, deliver the notification of a gpio pin being toggled to the
> > slave device.
>
> The GPIO device should expose its outbound GPIO lines
> as qdev gpio lines. The slave device should have a GPIO line
> which is an input qdev gpio. The board code then connects the two
> together using
>   qdev_connect_gpio_out(your_gpio_device, i,
>                         qdev_get_gpio_in(slavedevice, j));
>
> which connects the GPIO controller's output GPIO i to
> slave device's input GPIO j.
>
> There are also _named() versions of these so you can
> give GPIO lines names rather than having them be unnamed
> (which makes the code a bit easier to understand, especially
> where the device isn't a gpio controller whose outputs are
> all just "the GPIO lines").
>
> thanks
> -- PMM