RE: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended_msi

[Pavel Fedin <p.fedin@samsung.com>]

 Hello!

> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org] On Behalf Of Eric Auger
> Sent: Monday, June 29, 2015 6:37 PM
> To: eric.auger@st.com; eric.auger@linaro.org; linux-arm-kernel@lists.infradead.org;
> marc.zyngier@arm.com; christoffer.dall@linaro.org; andre.przywara@arm.com;
> kvmarm@lists.cs.columbia.edu; kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org; patches@linaro.org; p.fedin@samsung.com; pbonzini@redhat.com
> Subject: [PATCH 1/7] KVM: api: add kvm_irq_routing_extended_msi
> 
> On ARM, the MSI msg (address and data) comes along with
> out-of-band device ID information. The device ID encodes the device
> that composes the MSI msg. Let's create a new routing entry type,
> dubbed KVM_IRQ_ROUTING_EXTENDED_MSI and use the __u32 pad space
> to convey the device ID.
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> 
> ---
> 
> RFC -> PATCH
> - remove kvm_irq_routing_extended_msi and use union instead
> ---
>  Documentation/virtual/kvm/api.txt | 9 ++++++++-
>  include/uapi/linux/kvm.h          | 6 +++++-
>  2 files changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index d20fd94..6426ae9 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -1414,7 +1414,10 @@ struct kvm_irq_routing_entry {
>  	__u32 gsi;
>  	__u32 type;
>  	__u32 flags;
> -	__u32 pad;
> +	union {
> +		__u32 pad;
> +		__u32 devid;
> +	};
>  	union {
>  		struct kvm_irq_routing_irqchip irqchip;
>  		struct kvm_irq_routing_msi msi;

 devid is actually a part of MSI bunch. Shouldn't it be a part of struct kvm_irq_routing_msi then?
It also has reserved pad.

> @@ -1427,6 +1430,10 @@ struct kvm_irq_routing_entry {
>  #define KVM_IRQ_ROUTING_IRQCHIP 1
>  #define KVM_IRQ_ROUTING_MSI 2
>  #define KVM_IRQ_ROUTING_S390_ADAPTER 3
> +#define KVM_IRQ_ROUTING_EXTENDED_MSI 4
> +
> +In case of KVM_IRQ_ROUTING_EXTENDED_MSI routing type, devid is used to convey
> +the device ID.
> 
>  No flags are specified so far, the corresponding field must be set to zero.

What if we use KVM_MSI_VALID_DEVID flag instead of new KVM_IRQ_ROUTING_EXTENDED_MSI definition? I
believe this would make an API more consistent and introduce less new definitions.

> 
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 2a23705..8484681 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -841,12 +841,16 @@ struct kvm_irq_routing_s390_adapter {
>  #define KVM_IRQ_ROUTING_IRQCHIP 1
>  #define KVM_IRQ_ROUTING_MSI 2
>  #define KVM_IRQ_ROUTING_S390_ADAPTER 3
> +#define KVM_IRQ_ROUTING_EXTENDED_MSI 4
> 
>  struct kvm_irq_routing_entry {
>  	__u32 gsi;
>  	__u32 type;
>  	__u32 flags;
> -	__u32 pad;
> +	union {
> +		__u32 pad;
> +		__u32 devid;
> +	};
>  	union {
>  		struct kvm_irq_routing_irqchip irqchip;
>  		struct kvm_irq_routing_msi msi;
> --
> 1.9.1
> 
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Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia