linux-kernel - Re: [PATCH 1/7] genirq/msi: Add a new field in msi

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Message-ID: <7e77331c-4adf-5bb4-0c23-4d01a6ac5ab4@arm.com>
Date:   Tue, 23 Apr 2019 11:23:57 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Julien Grall <julien.grall@....com>, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org
Cc:     logang@...tatee.com, douliyangs@...il.com,
        miquel.raynal@...tlin.com, jason@...edaemon.net,
        tglx@...utronix.de, joro@...tes.org, robin.murphy@....com,
        bigeasy@...utronix.de, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH 1/7] genirq/msi: Add a new field in msi_desc to store an
 IOMMU cookie

Hi Julien,

On 18/04/2019 18:26, Julien Grall wrote:
> When an MSI doorbell is located downstream of an IOMMU, it is required
> to swizzle the physical address with an appropriately-mapped IOVA for any
> device attached to one of our DMA ops domain.
> 
> At the moment, the allocation of the mapping may be done when composing
> the message. However, the composing may be done in non-preemtible
> context while the allocation requires to be called from preemptible
> context.
> 
> A follow-up patch will split the current logic in two functions
> requiring to keep an IOMMU cookie per MSI.
> 
> This patch introduces a new field in msi_desc to store an IOMMU cookie
> when CONFIG_IOMMU_DMA is selected.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> ---
>  include/linux/msi.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/msi.h b/include/linux/msi.h
> index 7e9b81c3b50d..d7907feef1bb 100644
> --- a/include/linux/msi.h
> +++ b/include/linux/msi.h
> @@ -77,6 +77,9 @@ struct msi_desc {
>  	struct device			*dev;
>  	struct msi_msg			msg;
>  	struct irq_affinity_desc	*affinity;
> +#ifdef CONFIG_IOMMU_DMA
> +	const void			*iommu_cookie;
> +#endif
>  
>  	union {
>  		/* PCI MSI/X specific data */
> 

Given that this is the only member in this structure that is dependent
on a config option, you could also add a couple of accessors that would
do nothing when IOMMU_DMA is not selected (and use that in the DMA code).

Thanks,

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