Re: [PATCH V5 6/6] libxl: Allocate MMIO params for GPIO device and update DT

[Julien Grall <julien@xxxxxxx>]

(+ Bertrand)

Hi Viresh,

On 22/08/2022 10:15, Viresh Kumar wrote:
> This patch allocates Virtio MMIO params (IRQ and memory region) and pass
> them to the backend, also update Guest device-tree based on Virtio GPIO
> DT bindings [1].
>
> [1] 
> https://www.kernel.org/doc/Documentation/devicetree/bindings/gpio/gpio-virtio.yaml
>
> Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
>   tools/libs/light/libxl_arm.c | 51 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 51 insertions(+)
>
> diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
> index 4c1012e56893..86c1e560900f 100644
> --- a/tools/libs/light/libxl_arm.c
> +++ b/tools/libs/light/libxl_arm.c
> @@ -121,6 +121,15 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
>               return rc;
>       }
>   
> +    for (i = 0; i < d_config->num_gpios; i++) {
> +        libxl_device_gpio *gpio = &d_config->gpios[i];
> +    int rc = alloc_virtio_mmio_params(gc, &gpio->base, &gpio->irq,
> +                                      &virtio_mmio_base, &virtio_mmio_irq);
> +
> +    if (rc)
> +        return rc;
> +    }
> +
>       /*
>        * Every virtio-mmio device uses one emulated SPI. If Virtio devices are
>        * present, make sure that we allocate enough SPIs for them.
> @@ -984,6 +993,38 @@ static int make_virtio_mmio_node_i2c(libxl__gc *gc, void 
> *fdt, uint64_t base,
>       return fdt_end_node(fdt);
>   }
>   
> +static int make_virtio_mmio_node_gpio(libxl__gc *gc, void *fdt, uint64_t base,
> +                                      uint32_t irq, uint32_t backend_domid)
> +{
> +    int res;
> +
> +    res = make_virtio_mmio_node_common(gc, fdt, base, irq, backend_domid);
> +    if (res) return res;
> +
> +    res = fdt_begin_node(fdt, "gpio");
> +    if (res) return res;
> +
> +    res = fdt_property_compat(gc, fdt, 1, "virtio,device29");
It is a very descriptive compatible :). And yes I realize this is the 
compatible chosen by upstream.
> +    if (res) return res;
> +
> +    res = fdt_property(fdt, "gpio-controller", NULL, 0);
> +    if (res) return res;
> +
> +    res = fdt_property_cell(fdt, "#gpio-cells", 2);
> +    if (res) return res;
> +
> +    res = fdt_property(fdt, "interrupt-controller", NULL, 0);
> +    if (res) return res;
> +
> +    res = fdt_property_cell(fdt, "#interrupt-cells", 2);
> +    if (res) return res;
> +
> +    res = fdt_end_node(fdt);
> +    if (res) return res;
> +
> +    return fdt_end_node(fdt);
> +}
> +
>   static const struct arch_info *get_arch_info(libxl__gc *gc,
>                                                const struct xc_dom_image *dom)
>   {
> @@ -1317,6 +1358,16 @@ static int libxl__prepare_dtb(libxl__gc *gc, 
> libxl_domain_config *d_config,
>                                              i2c->backend_domid) );
>           }
>   
> +        for (i = 0; i < d_config->num_gpios; i++) {
> +            libxl_device_gpio *gpio = &d_config->gpios[i];
> +
> +            if (gpio->backend_domid != LIBXL_TOOLSTACK_DOMID)
> +                iommu_needed = true;
> +
> +            FDT( make_virtio_mmio_node_gpio(gc, fdt, gpio->base, gpio->irq,
> +                                            gpio->backend_domid) );
So this is exposing a GPIO interrupt controller but IIUC we will also 
need to describe the devices in the device-tree. Can you outline how you 
would expect it to work?
To put some context, this is related to what I wrote in patch #1. How 
much code will be necessary in libxl to add new device?
I am not the maintainer of this code, but I would expect some example 
how this can be used once this merged. This would help us to understand 
whether the interface is correct.
Cheers,

--
Julien Grall