RE: [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI irq domain

[Dey, Megha]

Hi Thomas,

> -----Original Message-----
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Sent: Wednesday, July 22, 2020 1:45 PM
> To: Jiang, Dave <dave.jiang@xxxxxxxxx>; vkoul@xxxxxxxxxx; Dey, Megha
> <megha.dey@xxxxxxxxx>; maz@xxxxxxxxxx; bhelgaas@xxxxxxxxxx;
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> Sanjay K <sanjay.k.kumar@xxxxxxxxx>; Luck, Tony <tony.luck@xxxxxxxxx>; Lin,
> Jing <jing.lin@xxxxxxxxx>; Williams, Dan J <dan.j.williams@xxxxxxxxx>;
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> Subject: Re: [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI irq domain
> 
> Dave Jiang <dave.jiang@xxxxxxxxx> writes:
> > From: Megha Dey <megha.dey@xxxxxxxxx>
> >
> > When DEV_MSI is enabled, the dev_msi_default_domain is updated to the
> > base DEV-MSI irq  domain. If interrupt remapping is enabled, we create
> 
> s/we//

ok
> 
> > a new IR-DEV-MSI irq domain and update the dev_msi_default domain to
> > the same.
> >
> > For X86, introduce a new irq_alloc_type which will be used by the
> > interrupt remapping driver.
> >
> > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Signed-off-by: Megha Dey <megha.dey@xxxxxxxxx>
> > Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
> > ---
> >  arch/x86/include/asm/hw_irq.h       |    1 +
> >  arch/x86/kernel/apic/msi.c          |   12 ++++++
> >  drivers/base/dev-msi.c              |   66 +++++++++++++++++++++++++++++++----
> >  drivers/iommu/intel/irq_remapping.c |   11 +++++-
> >  include/linux/intel-iommu.h         |    1 +
> >  include/linux/irqdomain.h           |   11 ++++++
> >  include/linux/msi.h                 |    3 ++
> 
> Why is this mixing generic code, x86 core code and intel specific driver code?
> This is new functionality so:
> 
>       1) Provide the infrastructure
>       2) Add support to architecture specific parts
>       3) Enable it

Ok, I will try to adhere to the layering next time around..
> 
> > +
> > +#ifdef CONFIG_DEV_MSI
> > +int dev_msi_prepare(struct irq_domain *domain, struct device *dev,
> > +			   int nvec, msi_alloc_info_t *arg) {
> > +	memset(arg, 0, sizeof(*arg));
> > +
> > +	arg->type = X86_IRQ_ALLOC_TYPE_DEV_MSI;
> > +
> > +	return 0;
> > +}
> > +#endif
> 
> What is this? Tons of new lines for taking up more space and not a single
> comment.

Hmm, I will add a comment..
> 
> > -static int dev_msi_prepare(struct irq_domain *domain, struct device
> > *dev,
> > +int __weak dev_msi_prepare(struct irq_domain *domain, struct device
> > +*dev,
> >  			   int nvec, msi_alloc_info_t *arg)  {
> >  	memset(arg, 0, sizeof(*arg));
> 
> Oh well. So every architecure which needs to override this and I assume all
> which are eventually going to support it need to do the memset() in their
> override.
> 
>        memset(arg,,,);
>        arch_dev_msi_prepare();
> 
> 
Per you suggestion, I have introduced arch_dev_msi_prepare which returns 0 by default unless
overridden by arch code in the next patch set.

> > -	dev_msi_default_domain = msi_create_irq_domain(fn,
> &dev_msi_domain_info, parent);
> > +	/*
> > +	 * This initcall may come after remap code is initialized. Ensure that
> > +	 * dev_msi_default domain is updated correctly.
> 
> What? No, this is a disgusting hack. Get your ordering straight, that's not rocket
> science.
> 

Hmm yeah, actually I realized we don't really need to have 2 new IRQ domains for dev-msi 
(with and without interrupt remapping enabled). Hence all this will go away in the next round
of patches.

> > +#ifdef CONFIG_IRQ_REMAP
> 
> IRQ_REMAP is x86 specific. Is this file x86 only or intended to be for general use?
> If it's x86 only, then this should be clearly documented. If not, then these
> x86'isms have no place here.

True, I will take care of this in the next patch set.
> 
> > +struct irq_domain *create_remap_dev_msi_irq_domain(struct irq_domain
> *parent,
> > +						   const char *name)
> 
> So we have msi_create_irq_domain() and this is about dev_msi, right? So can
> you please stick with a consistent naming scheme?

sure
> 
> > +{
> > +	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, &dev_msi_ir_domain_info,
> parent);
> > +	if (!domain) {
> > +		pr_warn("failed to initialize irqdomain for IR-DEV-MSI.\n");
> > +		return ERR_PTR(-ENXIO);
> > +	}
> > +
> > +	irq_domain_update_bus_token(domain,
> DOMAIN_BUS_PLATFORM_MSI);
> > +
> > +	if (!dev_msi_default_domain)
> > +		dev_msi_default_domain = domain;
> 
> Can this be called several times? If so, then this lacks a comment. If not, then
> this condition is useless.

Hmm this will go way in the next patch set, thank you for your input!
> 
> Thanks,
> 
>         tglx