linux-kernel - Re: [PATCH v7 5/8] genirq/irq: introduce msi_doorbell's structs and related callback

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Date:	Wed, 20 Apr 2016 10:16:08 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Eric Auger <eric.auger@...aro.org>, eric.auger@...com,
	robin.murphy@....com, alex.williamson@...hat.com,
	will.deacon@....com, joro@...tes.org, tglx@...utronix.de,
	jason@...edaemon.net, christoffer.dall@...aro.org,
	linux-arm-kernel@...ts.infradead.org
Cc:	patches@...aro.org, linux-kernel@...r.kernel.org,
	Bharat.Bhushan@...escale.com, pranav.sawargaonkar@...il.com,
	p.fedin@...sung.com, iommu@...ts.linux-foundation.org,
	Jean-Philippe.Brucker@....com, julien.grall@....com
Subject: Re: [PATCH v7 5/8] genirq/irq: introduce msi_doorbell's structs and
 related callback

On 19/04/16 18:13, Eric Auger wrote:
> The purpose is to be able to retrieve the MSI doorbells of an irqchip.
> This is now needed since on some platforms those doorbells must be
> iommu mapped (in case the MSIs transit through an IOMMU that do not
> bypass those transactions).
> 
> The assumption is there is a maximum of one doorbell region per cpu.
> The number of doorbells for the whole irqchip is stored in nb_doorbells.
> 
> A doorbell region is characterized by its physical address base, size and
> IOMMU protection flag.
> 
> irq_chip msi_doorbell_info callback enables to retrieve the doorbells of
> the irqchip.
> 
> Signed-off-by: Eric Auger <eric.auger@...aro.org>
> 
> ---
> 
> v7: creation
> ---
>  include/linux/irq.h | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/irq.h b/include/linux/irq.h
> index c4de623..fdad8c1 100644
> --- a/include/linux/irq.h
> +++ b/include/linux/irq.h
> @@ -312,9 +312,25 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
>  	return d->hwirq;
>  }
>  
> -/**
> - * struct irq_chip - hardware interrupt chip descriptor
> - *
> +/* MSI doorbell region */
> +struct irq_chip_msi_doorbell {
> +	phys_addr_t base;
> +	size_t size;
> +	int prot; /* iommu protection flag */

I find this one a bit scary. "int" is a probably not the right type if
it is a set of flags (it should describe both the protection and the
memory attributes - in this case, probably something like Device +
Writeable). You should probably use the same type the IOMMU code uses
(and if it is actually an int, then I'll shut up...).

> +};
> +
> +/*
> + * Describe all the MSI doorbell regions for an irqchip.
> + * A single doorbell region per cpu is assumed.
> + * In case a single doorbell is supported for the whole irqchip,
> + * the region is described in as cpu #0's one
> + */
> +struct irq_chip_msi_doorbell_info {
> +	struct irq_chip_msi_doorbell __percpu *percpu_doorbells;
> +	int nb_doorbells; /* overall number of doorbells */
> +};

How can size and prot be different from one CPU to another? It really
feels like they should be common. Can I suggest something like this?

struct irq_chip_msi_doorbell_info {
	phys_addr_t __percpu	*doorbells;
	size_t			size;
	u32			prot;
};

and get rid of struct irq_chip_msi_doorbell altogether?

> +
> +/** * struct irq_chip - hardware interrupt chip descriptor *
>   * @name:		name for /proc/interrupts
>   * @irq_startup:	start up the interrupt (defaults to ->enable if NULL)
>   * @irq_shutdown:	shut down the interrupt (defaults to ->disable if NULL)
> @@ -349,6 +365,7 @@ static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
>   * @irq_get_irqchip_state:	return the internal state of an interrupt
>   * @irq_set_irqchip_state:	set the internal state of a interrupt
>   * @irq_set_vcpu_affinity:	optional to target a vCPU in a virtual machine
> + * @msi_doorbell_info:	return the MSI doorbell info
>   * @ipi_send_single:	send a single IPI to destination cpus
>   * @ipi_send_mask:	send an IPI to destination cpus in cpumask
>   * @flags:		chip specific flags
> @@ -394,7 +411,8 @@ struct irq_chip {
>  	int		(*irq_set_irqchip_state)(struct irq_data *data, enum irqchip_irq_state which, bool state);
>  
>  	int		(*irq_set_vcpu_affinity)(struct irq_data *data, void *vcpu_info);
> -
> +	const struct irq_chip_msi_doorbell_info *(*msi_doorbell_info)(
> +							struct irq_data *data);
>  	void		(*ipi_send_single)(struct irq_data *data, unsigned int cpu);
>  	void		(*ipi_send_mask)(struct irq_data *data, const struct cpumask *dest);
>  
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...