linux-kernel - Re: [PATCH v14 04/16] iommu/dma: MSI doorbell alloc/free

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Message-ID: <87lgxrqijs.fsf@e105922-lin.cambridge.arm.com>
Date:   Fri, 14 Oct 2016 12:25:11 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, christoffer.dall@...aro.org,
        marc.zyngier@....com, robin.murphy@....com,
        alex.williamson@...hat.com, will.deacon@....com, joro@...tes.org,
        tglx@...utronix.de, jason@...edaemon.net,
        linux-arm-kernel@...ts.infradead.org, drjones@...hat.com,
        kvm@...r.kernel.org, Manish.Jaggi@...iumnetworks.com,
        p.fedin@...sung.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, pranav.sawargaonkar@...il.com,
        yehuday@...vell.com
Subject: Re: [PATCH v14 04/16] iommu/dma: MSI doorbell alloc/free

Hi Eric,

One query and a comment below.

Eric Auger <eric.auger@...hat.com> writes:

> We introduce the capability to (un)register MSI doorbells.
>
> A doorbell region is characterized by its physical address base, size,
> and whether it its safe (ie. it implements IRQ remapping). A doorbell
> can be per-cpu or global. We currently only care about global doorbells.
>
> A function returns whether all registered doorbells are safe.
>
> MSI controllers likely to work along with IOMMU that translate MSI
> transaction must register their doorbells to allow device assignment
> with MSI support.  Otherwise the MSI transactions will cause IOMMU faults.
>
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>
> ---
>
> v13 -> v14:
> - previously in msi-doorbell.h/c
> ---
>  drivers/iommu/dma-iommu.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-iommu.h | 41 ++++++++++++++++++++++++++
>  2 files changed, 116 insertions(+)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index d45f9a0..d8a7d86 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -43,6 +43,38 @@ struct iommu_dma_cookie {
>  	spinlock_t		msi_lock;
>  };
>  
> +/**
> + * struct iommu_msi_doorbell_info - MSI doorbell region descriptor
> + * @percpu_doorbells: per cpu doorbell base address
> + * @global_doorbell: base address of the doorbell
> + * @doorbell_is_percpu: is the doorbell per cpu or global?
> + * @safe: true if irq remapping is implemented
> + * @size: size of the doorbell
> + */
> +struct iommu_msi_doorbell_info {
> +	union {
> +		phys_addr_t __percpu    *percpu_doorbells;

Out of curiosity, have you come across systems that have per-cpu
doorbells? I couldn't find a system that'd help solidify my
understanding on it's usage.

> +		phys_addr_t             global_doorbell;
> +	};
> +	bool    doorbell_is_percpu;
> +	bool    safe;

Although you've got the comment above, 'safe' doesn't quite convey it's
purpose. Can this be renamed to something more descriptive -
'intr_remapping' or 'intr_isolation' perhaps?

Thanks,
Punit


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