Re: [patch V2 29/46] irqdomain/msi: Allow to override msi_domain_alloc/free_irqs()

["Dey, Megha" <megha.dey@intel.com>]

Hi Thomas,

On 8/26/2020 4:16 AM, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> To support MSI irq domains which do not fit at all into the regular MSI
> irqdomain scheme, like the XEN MSI interrupt management for PV/HVM/DOM0,
> it's necessary to allow to override the alloc/free implementation.
>
> This is a preperatory step to switch X86 away from arch_*_msi_irqs() and
> store the irq domain pointer right in struct device.
>
> No functional change for existing MSI irq domain users.
>
> Aside of the evil XEN wrapper this is also useful for special MSI domains
> which need to do extra alloc/free work before/after calling the generic
> core function. Work like allocating/freeing MSI descriptors, MSI storage
> space etc.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
> ---
>   include/linux/msi.h |   27 ++++++++++++++++++++
>   kernel/irq/msi.c    |   70 +++++++++++++++++++++++++++++++++++-----------------
>   2 files changed, 75 insertions(+), 22 deletions(-)
>
> --- a/include/linux/msi.h
> +++ b/include/linux/msi.h
> @@ -241,6 +241,10 @@ struct msi_domain_info;
>    * @msi_finish:		Optional callback to finalize the allocation
>    * @set_desc:		Set the msi descriptor for an interrupt
>    * @handle_error:	Optional error handler if the allocation fails
> + * @domain_alloc_irqs:	Optional function to override the default allocation
> + *			function.
> + * @domain_free_irqs:	Optional function to override the default free
> + *			function.
>    *
>    * @get_hwirq, @msi_init and @msi_free are callbacks used by
>    * msi_create_irq_domain() and related interfaces
> @@ -248,6 +252,22 @@ struct msi_domain_info;
>    * @msi_check, @msi_prepare, @msi_finish, @set_desc and @handle_error
>    * are callbacks used by msi_domain_alloc_irqs() and related
>    * interfaces which are based on msi_desc.
> + *
> + * @domain_alloc_irqs, @domain_free_irqs can be used to override the
> + * default allocation/free functions (__msi_domain_alloc/free_irqs). This
> + * is initially for a wrapper around XENs seperate MSI universe which can't
> + * be wrapped into the regular irq domains concepts by mere mortals.  This
> + * allows to universally use msi_domain_alloc/free_irqs without having to
> + * special case XEN all over the place.
> + *
> + * Contrary to other operations @domain_alloc_irqs and @domain_free_irqs
> + * are set to the default implementation if NULL and even when
> + * MSI_FLAG_USE_DEF_DOM_OPS is not set to avoid breaking existing users and
> + * because these callbacks are obviously mandatory.
> + *
> + * This is NOT meant to be abused, but it can be useful to build wrappers
> + * for specialized MSI irq domains which need extra work before and after
> + * calling __msi_domain_alloc_irqs()/__msi_domain_free_irqs().
>    */
>   struct msi_domain_ops {
>   	irq_hw_number_t	(*get_hwirq)(struct msi_domain_info *info,
> @@ -270,6 +290,10 @@ struct msi_domain_ops {
>   				    struct msi_desc *desc);
>   	int		(*handle_error)(struct irq_domain *domain,
>   					struct msi_desc *desc, int error);
> +	int		(*domain_alloc_irqs)(struct irq_domain *domain,
> +					     struct device *dev, int nvec);
> +	void		(*domain_free_irqs)(struct irq_domain *domain,
> +					    struct device *dev);
>   };
>   
>   /**
> @@ -327,8 +351,11 @@ int msi_domain_set_affinity(struct irq_d
>   struct irq_domain *msi_create_irq_domain(struct fwnode_handle *fwnode,
>   					 struct msi_domain_info *info,
>   					 struct irq_domain *parent);
> +int __msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
> +			    int nvec);
>   int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
>   			  int nvec);
> +void __msi_domain_free_irqs(struct irq_domain *domain, struct device *dev);
>   void msi_domain_free_irqs(struct irq_domain *domain, struct device *dev);
>   struct msi_domain_info *msi_get_domain_info(struct irq_domain *domain);
>   
> --- a/kernel/irq/msi.c
> +++ b/kernel/irq/msi.c
> @@ -229,11 +229,13 @@ static int msi_domain_ops_check(struct i
>   }
>   
>   static struct msi_domain_ops msi_domain_ops_default = {
> -	.get_hwirq	= msi_domain_ops_get_hwirq,
> -	.msi_init	= msi_domain_ops_init,
> -	.msi_check	= msi_domain_ops_check,
> -	.msi_prepare	= msi_domain_ops_prepare,
> -	.set_desc	= msi_domain_ops_set_desc,
> +	.get_hwirq		= msi_domain_ops_get_hwirq,
> +	.msi_init		= msi_domain_ops_init,
> +	.msi_check		= msi_domain_ops_check,
> +	.msi_prepare		= msi_domain_ops_prepare,
> +	.set_desc		= msi_domain_ops_set_desc,
> +	.domain_alloc_irqs	= __msi_domain_alloc_irqs,
> +	.domain_free_irqs	= __msi_domain_free_irqs,
>   };
>   
>   static void msi_domain_update_dom_ops(struct msi_domain_info *info)
> @@ -245,6 +247,14 @@ static void msi_domain_update_dom_ops(st
>   		return;
>   	}
>   
> +	if (ops->domain_alloc_irqs == NULL)
> +		ops->domain_alloc_irqs = msi_domain_ops_default.domain_alloc_irqs;
> +	if (ops->domain_free_irqs == NULL)
> +		ops->domain_free_irqs = msi_domain_ops_default.domain_free_irqs;
> +
> +	if (!(info->flags & MSI_FLAG_USE_DEF_DOM_OPS))
> +		return;
> +
>   	if (ops->get_hwirq == NULL)
>   		ops->get_hwirq = msi_domain_ops_default.get_hwirq;
>   	if (ops->msi_init == NULL)
> @@ -278,8 +288,7 @@ struct irq_domain *msi_create_irq_domain
>   {
>   	struct irq_domain *domain;
>   
> -	if (info->flags & MSI_FLAG_USE_DEF_DOM_OPS)
> -		msi_domain_update_dom_ops(info);
> +	msi_domain_update_dom_ops(info);
>   	if (info->flags & MSI_FLAG_USE_DEF_CHIP_OPS)
>   		msi_domain_update_chip_ops(info);
>   
> @@ -386,17 +395,8 @@ static bool msi_check_reservation_mode(s
>   	return desc->msi_attrib.is_msix || desc->msi_attrib.maskbit;
>   }
>   
> -/**
> - * msi_domain_alloc_irqs - Allocate interrupts from a MSI interrupt domain
> - * @domain:	The domain to allocate from
> - * @dev:	Pointer to device struct of the device for which the interrupts
> - *		are allocated
> - * @nvec:	The number of interrupts to allocate
> - *
> - * Returns 0 on success or an error code.
> - */
> -int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
> -			  int nvec)
> +int __msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
> +			    int nvec)
>   {
>   	struct msi_domain_info *info = domain->host_data;
>   	struct msi_domain_ops *ops = info->ops;
> @@ -490,12 +490,24 @@ int msi_domain_alloc_irqs(struct irq_dom
>   }
>   
>   /**
> - * msi_domain_free_irqs - Free interrupts from a MSI interrupt @domain associated tp @dev
> - * @domain:	The domain to managing the interrupts
> + * msi_domain_alloc_irqs - Allocate interrupts from a MSI interrupt domain
> + * @domain:	The domain to allocate from
>    * @dev:	Pointer to device struct of the device for which the interrupts
> - *		are free
> + *		are allocated
> + * @nvec:	The number of interrupts to allocate
> + *
> + * Returns 0 on success or an error code.
>    */
> -void msi_domain_free_irqs(struct irq_domain *domain, struct device *dev)
> +int msi_domain_alloc_irqs(struct irq_domain *domain, struct device *dev,
> +			  int nvec)
> +{
> +	struct msi_domain_info *info = domain->host_data;
> +	struct msi_domain_ops *ops = info->ops;
> +
> +	return ops->domain_alloc_irqs(domain, dev, nvec);
> +}
> +

Since, our upcoming driver will directly call this API, an 
EXPORT_SYMBOL_GPL tag would be required.

Currently there is no use case. I was wondering if we should add this 
change while submitting the

idxd/ims patches or would you add this to this patch?

> +void __msi_domain_free_irqs(struct irq_domain *domain, struct device *dev)
>   {
>   	struct msi_desc *desc;
>   
> @@ -513,6 +525,20 @@ void msi_domain_free_irqs(struct irq_dom
>   }
>   
>   /**
> + * __msi_domain_free_irqs - Free interrupts from a MSI interrupt @domain associated tp @dev
> + * @domain:	The domain to managing the interrupts
> + * @dev:	Pointer to device struct of the device for which the interrupts
> + *		are free
> + */
> +void msi_domain_free_irqs(struct irq_domain *domain, struct device *dev)
> +{
> +	struct msi_domain_info *info = domain->host_data;
> +	struct msi_domain_ops *ops = info->ops;
> +
> +	return ops->domain_free_irqs(domain, dev);
> +}
> +
> +/**
>    * msi_get_domain_info - Get the MSI interrupt domain info for @domain
>    * @domain:	The interrupt domain to retrieve data from
>    *
>
>