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

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Date:   Wed, 22 Jul 2020 10:03:45 -0700
From:   "Dey, Megha" <megha.dey@...el.com>
To:     Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>
CC:     <vkoul@...nel.org>, <maz@...nel.org>, <bhelgaas@...gle.com>,
        <rafael@...nel.org>, <gregkh@...uxfoundation.org>,
        <tglx@...utronix.de>, <hpa@...or.com>,
        <alex.williamson@...hat.com>, <jacob.jun.pan@...el.com>,
        <ashok.raj@...el.com>, <yi.l.liu@...el.com>, <baolu.lu@...el.com>,
        <kevin.tian@...el.com>, <sanjay.k.kumar@...el.com>,
        <tony.luck@...el.com>, <jing.lin@...el.com>,
        <dan.j.williams@...el.com>, <kwankhede@...dia.com>,
        <eric.auger@...hat.com>, <parav@...lanox.com>,
        <dave.hansen@...el.com>, <netanelg@...lanox.com>,
        <shahafs@...lanox.com>, <yan.y.zhao@...ux.intel.com>,
        <pbonzini@...hat.com>, <samuel.ortiz@...el.com>,
        <mona.hossain@...el.com>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        <linux-pci@...r.kernel.org>, <kvm@...r.kernel.org>
Subject: Re: [PATCH RFC v2 03/18] irq/dev-msi: Create IR-DEV-MSI irq domain

Hi Dan,

On 7/21/2020 9:21 AM, Jason Gunthorpe wrote:
> On Tue, Jul 21, 2020 at 09:02:35AM -0700, Dave Jiang wrote:
>> From: Megha Dey <megha.dey@...el.com>
>>
>> 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
>> 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.
> 
> Why? Shouldn't this by symmetrical with normal MSI? Does MSI do this?

Since I am introducing the new dev msi domain for the case when IR_REMAP 
is turned on, I have introduced the new type in this patch.

MSI/MSIX have their own irq alloc types which are also only used by the 
intel remapping driver..

> 
> I would have thought you'd want to switch to this remapping mode as
> part of vfio or something like current cases.

Can you let me know what current case you are referring to?
> 
>> +struct irq_domain *create_remap_dev_msi_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, &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;
>> +
>> +	return domain;
>> +}
> 
> What about this code creates a "remap" ? ie why is the function called
> "create_remap" ?

Well, this function creates a new domain for the case when IR_REMAP is 
enabled, hence I called it create_remap...

> 
>> diff --git a/include/linux/msi.h b/include/linux/msi.h
>> index 1da97f905720..7098ba566bcd 100644
>> +++ b/include/linux/msi.h
>> @@ -378,6 +378,9 @@ void *platform_msi_get_host_data(struct irq_domain *domain);
>>   void platform_msi_write_msg(struct irq_data *data, struct msi_msg *msg);
>>   void platform_msi_unmask_irq(struct irq_data *data);
>>   void platform_msi_mask_irq(struct irq_data *data);
>> +
>> +int dev_msi_prepare(struct irq_domain *domain, struct device *dev,
>> +                           int nvec, msi_alloc_info_t *arg);
> 
> I wonder if this should use the popular #ifdef dev_msi_prepare scheme
> instead of a weak symbol?

Ok, I will look into the #ifdef option.
> 
> Jason
>