Re: [patch 28/33] PCI/MSI: Provide IMS (Interrupt Message Store) support

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Nov 11, 2022 at 02:58:55PM +0100, Thomas Gleixner wrote:
> IMS (Interrupt Message Store) is a new specification which allows
> implementation specific storage of MSI messages contrary to the
> strict standard specified MSI and MSI-X message stores.
> 
> This requires new device specific interrupt domains to handle the
> implementation defined storage which can be an array in device memory or
> host/guest memory which is shared with hardware queues.
> 
> Add a function to create IMS domains for PCI devices. IMS domains are using
> the new per device domain mechanism and are configured by the device driver
> via a template. IMS domains are created as secondary device domains so they
> work side on side with MSI[-X] on the same device.
> 
> The IMS domains have a few constraints:
> 
>   - The index space is managed by the core code.
> 
>     Device memory based IMS provides a storage array with a fixed size
>     which obviously requires an index. But there is no association between
>     index and functionality so the core can randomly allocate an index in
>     the array.
> 
>     Queue memory based IMS does not have the concept of an index as the
>     storage is somewhere in memory. In that case the index is purely
>     software based to keep track of the allocations.
> 
>   - There is no requirement for consecutive index ranges
> 
>     This is currently a limitation of the MSI core and can be implemented
>     if there is a justified use case by changing the internal storage from
>     xarray to maple_tree. For now it's single vector allocation.
> 
>   - The interrupt chip must provide the following callbacks:
> 
>   	- irq_mask()
> 	- irq_unmask()
> 	- irq_write_msi_msg()
> 
>    - The interrupt chip must provide the following optional callbacks
>      when the irq_mask(), irq_unmask() and irq_write_msi_msg() callbacks
>      cannot operate directly on hardware, e.g. in the case that the
>      interrupt message store is in queue memory:
> 
>      	- irq_bus_lock()
> 	- irq_bus_unlock()
> 
>      These callbacks are invoked from preemptible task context and are
>      allowed to sleep. In this case the mandatory callbacks above just
>      store the information. The irq_bus_unlock() callback is supposed to
>      make the change effective before returning.
> 
>    - Interrupt affinity setting is handled by the underlying parent
>      interrupt domain and communicated to the IMS domain via
>      irq_write_msi_msg(). IMS domains cannot have a irq_set_affinity()
>      callback. That's a reasonable restriction similar to the PCI/MSI
>      device domain implementations.
> 
> The domain is automatically destroyed when the PCI device is removed.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

A couple typos below.

> ---
>  drivers/pci/msi/irqdomain.c |   59 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci.h         |    5 +++
>  2 files changed, 64 insertions(+)
> 
> --- a/drivers/pci/msi/irqdomain.c
> +++ b/drivers/pci/msi/irqdomain.c
> @@ -355,6 +355,65 @@ bool pci_msi_domain_supports(struct pci_
>  	return (supported & feature_mask) == feature_mask;
>  }
>  
> +/**
> + * pci_create_ims_domain - Create a secondary IMS domain for a PCI device
> + * @pdev:	The PCI device to operate on
> + * @template:	The MSI info template which describes the domain
> + * @hwsize:	The size of the hardware entry table or 0 if the domain
> + *		is purely software managed
> + * @data:	Optional pointer to domain specific data to be stored
> + *		in msi_domain_info::data
> + *
> + * Return: True on success, false otherwise
> + *
> + * A IMS domain is expected to have the following constraints:

An IMS ...

> + *	- The index space is managed by the core code
> + *
> + *	- There is no requirement for consecutive index ranges
> + *
> + *	- The interrupt chip must provide the following callbacks:
> + *		- irq_mask()
> + *		- irq_unmask()
> + *		- irq_write_msi_msg()
> + *
> + *	- The interrupt chip must provide the following optional callbacks
> + *	  when the irq_mask(), irq_unmask() and irq_write_msi_msg() callbacks
> + *	  cannot operate directly on hardware, e.g. in the case that the
> + *	  interrupt message store is in queue memory:
> + *		- irq_bus_lock()
> + *		- irq_bus_unlock()
> + *
> + *	  These callbacks are invoked from preemptible task context and are
> + *	  allowed to sleep. In this case the mandatory callbacks above just
> + *	  store the information. The irq_bus_unlock() callback is supposed
> + *	  to make the change effective before returning.
> + *
> + *     - Interrupt affinity setting is handled by the underlying parent
> + *	 interrupt domain and communicated to the IMS domain via
> + *	 irq_write_msi_msg().

Different indentation than the bullet items above.

> + *
> + * The domain is automatically destroyed when the PCI device is removed.
> + */
> +bool pci_create_ims_domain(struct pci_dev *pdev, const struct msi_domain_template *template,
> +			   unsigned int hwsize, void *data)
> +{
> +	struct irq_domain *domain = dev_get_msi_domain(&pdev->dev);
> +
> +	if (!domain || !irq_domain_is_msi_parent(domain))
> +		return -ENOTSUPP;
> +
> +	if (template->info.bus_token != DOMAIN_BUS_PCI_DEVICE_IMS ||
> +	    !(template->info.flags & MSI_FLAG_ALLOC_SIMPLE_MSI_DESCS) ||
> +	    !(template->info.flags & MSI_FLAG_FREE_MSI_DESCS) ||
> +	    !template->chip.irq_mask || !template->chip.irq_unmask ||
> +	    !template->chip.irq_write_msi_msg || template->chip.irq_set_affinity)
> +		return -EINVAL;
> +
> +	return msi_create_device_irq_domain(&pdev->dev, MSI_SECONDARY_DOMAIN, template,
> +					    hwsize, data, NULL);
> +}
> +EXPORT_SYMBOL_GPL(pci_create_ims_domain);
> +
>  /*
>   * Users of the generic MSI infrastructure expect a device to have a single ID,
>   * so with DMA aliases we have to pick the least-worst compromise. Devices with
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2481,6 +2481,11 @@ static inline bool pci_is_thunderbolt_at
>  void pci_uevent_ers(struct pci_dev *pdev, enum  pci_ers_result err_type);
>  #endif
>  
> +struct msi_domain_template;
> +
> +bool pci_create_ims_domain(struct pci_dev *pdev, const struct msi_domain_template *template,
> +			   unsigned int hwsize, void *data);
> +
>  #include <linux/dma-mapping.h>
>  
>  #define pci_printk(level, pdev, fmt, arg...) \
>