linux-kernel - Re: [PATCH v3 1/7] iommu/arm-smmu-v3: Introduce SMMU option PAGE0_REGS

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Date:   Sat, 6 May 2017 01:03:28 +0200
From:   Robert Richter <rric@...nel.org>
To:     Geetha sowjanya <gakula@...iumnetworks.com>
Cc:     will.deacon@....com, robin.murphy@....com,
        lorenzo.pieralisi@....com, hanjun.guo@...aro.org,
        sudeep.holla@....com, iommu@...ts.linux-foundation.org,
        jcm@...hat.com, linux-kernel@...r.kernel.org,
        robert.richter@...ium.com, catalin.marinas@....com,
        sgoutham@...ium.com, linux-arm-kernel@...ts.infradead.org,
        linux-acpi@...r.kernel.org, geethasowjanya.akula@...il.com,
        linu.cherian@...ium.com, Charles.Garcia-Tobin@....com,
        Geetha Sowjanya <geethasowjanya.akula@...ium.com>
Subject: Re: [PATCH v3 1/7] iommu/arm-smmu-v3: Introduce SMMU option
 PAGE0_REGS_ONLY for ThunderX2 errata #74

On 05.05.17 17:38:05, Geetha sowjanya wrote:
> From: Linu Cherian <linu.cherian@...ium.com>
> 
> Cavium ThunderX2 SMMU implementation doesn't support page 1 register space
> and PAGE0_REGS_ONLY option will be enabled as an errata workaround.
> 
> This option when turned on, replaces all page 1 offsets used for
> EVTQ_PROD/CONS, PRIQ_PROD/CONS register access with page 0 offsets.
> 
> Signed-off-by: Linu Cherian <linu.cherian@...ium.com>
> Signed-off-by: Geetha Sowjanya <geethasowjanya.akula@...ium.com>
> ---
>  .../devicetree/bindings/iommu/arm,smmu-v3.txt      |  6 +++
>  drivers/iommu/arm-smmu-v3.c                        | 44 ++++++++++++++++------
>  2 files changed, 38 insertions(+), 12 deletions(-)

> @@ -1995,8 +2011,10 @@ static int arm_smmu_init_queues(struct arm_smmu_device *smmu)
>  	if (!(smmu->features & ARM_SMMU_FEAT_PRI))
>  		return 0;
>  
> -	return arm_smmu_init_one_queue(smmu, &smmu->priq.q, ARM_SMMU_PRIQ_PROD,
> -				       ARM_SMMU_PRIQ_CONS, PRIQ_ENT_DWORDS);
> +	return arm_smmu_init_one_queue(smmu, &smmu->priq.q,
> +				       ARM_SMMU_PRIQ_PROD(smmu),
> +				       ARM_SMMU_PRIQ_CONS(smmu),
> +				       PRIQ_ENT_DWORDS);

I would also suggest Robin's idea from the v1 review here. This works
if we rework arm_smmu_init_one_queue() to pass addresses instead of
offsets.

This would make these widespread offset calculations obsolete.

-Robert