Re: [PATCH v4 09/22] KVM: arm64: ITS: Report the ITE size in GITS_TYPER

[Marc Zyngier <marc.zyngier@arm.com>]

On Mon, Mar 27 2017 at 10:30:59 AM, Eric Auger <eric.auger@redhat.com> wrote:
> An ITE size of 8 Bytes is reported to the guest. Combining this
> information with the number of event IDs the guest wants to support,
> this latter will be able to allocate each device's ITT with the
> right size.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Reviewed-by: Andre Przywara <andre.przywara@arm.com>
>
> ---
>
> v2 -> v3:
> - changed (u64)(VITS_ESZ - 1) to (VITS_ESZ - 1ULL) in
>   vgic_register_its_iodev
> - added Andre's R-b
>
> v1 -> v2:
> - correct ITT_ENTRY_SIZE field
> - remove ITE_SIZE since all entries become 8 bytes
> ---
>  include/linux/irqchip/arm-gic-v3.h | 1 +
>  virt/kvm/arm/vgic/vgic-its.c       | 5 ++++-
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index 97cbca1..d86f963 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -232,6 +232,7 @@
>  #define GITS_CTLR_QUIESCENT		(1U << 31)
>  
>  #define GITS_TYPER_PLPIS		(1UL << 0)
> +#define GITS_TYPER_ITT_ENTRY_SIZE_SHIFT	4
>  #define GITS_TYPER_IDBITS_SHIFT		8
>  #define GITS_TYPER_DEVBITS_SHIFT	13
>  #define GITS_TYPER_DEVBITS(r)		((((r) >> GITS_TYPER_DEVBITS_SHIFT) & 0x1f) + 1)
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 169b486..fabcac1 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -179,6 +179,8 @@ static struct its_ite *find_ite(struct vgic_its *its, u32 device_id,
>  
>  #define GIC_LPI_OFFSET 8192
>  
> +#define VITS_ESZ 8
> +
>  /*
>   * Finds and returns a collection in the ITS collection table.
>   * Must be called with the its_lock mutex held.
> @@ -379,6 +381,7 @@ static unsigned long vgic_mmio_read_its_typer(struct kvm *kvm,
>  	 */
>  	reg |= 0x0f << GITS_TYPER_DEVBITS_SHIFT;
>  	reg |= 0x0f << GITS_TYPER_IDBITS_SHIFT;
> +	reg |= (VITS_ESZ - 1) << GITS_TYPER_ITT_ENTRY_SIZE_SHIFT;
>  
>  	return extract_bytes(reg, addr & 7, len);
>  }
> @@ -1436,7 +1439,7 @@ static int vgic_register_its_iodev(struct kvm *kvm, struct vgic_its *its)
>  	(GIC_BASER_CACHEABILITY(GITS_BASER, INNER, RaWb)		| \
>  	 GIC_BASER_CACHEABILITY(GITS_BASER, OUTER, SameAsInner)		| \
>  	 GIC_BASER_SHAREABILITY(GITS_BASER, InnerShareable)		| \
> -	 ((8ULL - 1) << GITS_BASER_ENTRY_SIZE_SHIFT)			| \
> +	 ((VITS_ESZ - 1ULL) << GITS_BASER_ENTRY_SIZE_SHIFT)		| \
>  	 GITS_BASER_PAGE_SIZE_64K)
>  
>  #define INITIAL_PROPBASER_VALUE						  \

nit: since we're going to now encode a number of sizes in various
registers, I have the feeling that it would make sense to have a macro
that performs that encoding in a relatively generic way.

Something along the lines of

#define GIC_ENCODE_SZ(n,w) (((unsigned long)(n) - 1) & GENMASK_ULL(((w) - 1), 0))

where n is the value, and w is the number of bits required. Somehow, I'd
find it slightly more readable. Or do you think that it is completely
overkill?

Thanks,

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