Re: [PATCH RFC 04/15] drivers/base: Add support for a new IMS irq domain

[Jason Gunthorpe]

On Tue, Apr 21, 2020 at 04:34:11PM -0700, Dave Jiang wrote:
> diff --git a/drivers/base/ims-msi.c b/drivers/base/ims-msi.c
> new file mode 100644
> index 000000000000..738f6d153155
> +++ b/drivers/base/ims-msi.c
> @@ -0,0 +1,100 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Support for Device Specific IMS interrupts.
> + *
> + * Copyright  2019 Intel Corporation.
> + *
> + * Author: Megha Dey <megha.dey@xxxxxxxxx>
> + */
> +
> +#include <linux/dmar.h>
> +#include <linux/irq.h>
> +#include <linux/mdev.h>
> +#include <linux/pci.h>
> +
> +/*
> + * Determine if a dev is mdev or not. Return NULL if not mdev device.
> + * Return mdev's parent dev if success.
> + */
> +static inline struct device *mdev_to_parent(struct device *dev)
> +{
> +	struct device *ret = NULL;
> +	struct device *(*fn)(struct device *dev);
> +	struct bus_type *bus = symbol_get(mdev_bus_type);
> +
> +	if (bus && dev->bus == bus) {
> +		fn = symbol_get(mdev_dev_to_parent_dev);
> +		ret = fn(dev);
> +		symbol_put(mdev_dev_to_parent_dev);
> +		symbol_put(mdev_bus_type);

No, things like this are not OK in the drivers/base

Whatever this is doing needs to be properly architected in some
generic way.

> +static int dev_ims_prepare(struct irq_domain *domain, struct device *dev,
> +			   int nvec, msi_alloc_info_t *arg)
> +{
> +	if (dev_is_mdev(dev))
> +		dev = mdev_to_parent(dev);

Like maybe the caller shouldn't be passing in a mdev in the first
place, or some generic driver layer scheme is needed to go from a
child device (eg a mdev or one of these new virtual bus things) to the
struct device that owns the IRQ interface.

> +	init_irq_alloc_info(arg, NULL);
> +	arg->dev = dev;
> +	arg->type = X86_IRQ_ALLOC_TYPE_IMS;

Also very bewildering to see X86_* in drivers/base

> +struct irq_domain *arch_create_ims_irq_domain(struct irq_domain *parent,
> +					      const char *name)
> +{
> +	struct fwnode_handle *fn;
> +	struct irq_domain *domain;
> +
> +	fn = irq_domain_alloc_named_fwnode(name);
> +	if (!fn)
> +		return NULL;
> +
> +	domain = msi_create_irq_domain(fn, &ims_ir_domain_info, parent);
> +	if (!domain)
> +		return NULL;
> +
> +	irq_domain_update_bus_token(domain, DOMAIN_BUS_PLATFORM_MSI);
> +	irq_domain_free_fwnode(fn);
> +
> +	return domain;
> +}

I'm still not really clear why all this is called IMS.. This looks
like the normal boilerplate to setup an IRQ domain? What is actually
'ims' in here?

> diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h
> index 7d922950caaf..c21f1305a76b 100644
> +++ b/drivers/vfio/mdev/mdev_private.h
> @@ -36,7 +36,6 @@ struct mdev_device {
>  };
>  
>  #define to_mdev_device(dev)	container_of(dev, struct mdev_device, dev)
> -#define dev_is_mdev(d)		((d)->bus == &mdev_bus_type)
>  
>  struct mdev_type {
>  	struct kobject kobj;
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 0ce30ca78db0..fa2344e239ef 100644
> +++ b/include/linux/mdev.h
> @@ -144,5 +144,8 @@ void mdev_unregister_driver(struct mdev_driver *drv);
>  struct device *mdev_parent_dev(struct mdev_device *mdev);
>  struct device *mdev_dev(struct mdev_device *mdev);
>  struct mdev_device *mdev_from_dev(struct device *dev);
> +struct device *mdev_dev_to_parent_dev(struct device *dev);
> +
> +#define dev_is_mdev(dev) ((dev)->bus == symbol_get(mdev_bus_type))

NAK on the symbol_get

Jason