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

[Jason Gunthorpe]

On Fri, May 01, 2020 at 03:30:02PM -0700, Dey, Megha wrote:
> Hi Jason,
> 
> On 4/23/2020 1:11 PM, Jason Gunthorpe wrote:
> > 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.
> 
> Basically what I am trying to do here is to determine if the device is an
> mdev device or not.

Why? mdev devices are virtual they don't have HW elements.

The caller should use the concrete pci_device to allocate
platform_msi? What is preventing this?

> > > +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?
> 
> It is just a way to create a new domain specifically for IMS interrupts.
> Although, since there is a platform_msi_create_irq_domain already, which
> does something similar, I will use the same for IMS as well.

But this is all code already intended to be used by the platform, why
is it in drivers/base?

> Also, since there is quite a stir over the name 'IMS' do you have any
> suggestion for a more generic name for this?

It seems we have a name, this is called platform_msi in Linux?

Jason