linux-kernel - RE: [PATCH 3/7] iommu/arm-smmu: Add tlb

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Date:   Fri, 30 Aug 2019 18:05:19 +0000
From:   Krishna Reddy <vdumpa@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
CC:     Sachin Nikam <Snikam@...dia.com>,
        "Thomas Zeng (SW-TEGRA)" <thomasz@...dia.com>,
        Juha Tukkinen <jtukkinen@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Pritesh Raithatha <praithatha@...dia.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Timo Alho <talho@...dia.com>, Yu-Huan Hsu <YHsu@...dia.com>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        Thierry Reding <treding@...dia.com>,
        Alexander Van Brunt <avanbrunt@...dia.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "will.deacon@....com" <will.deacon@....com>,
        "joro@...tes.org" <joro@...tes.org>
Subject: RE: [PATCH 3/7] iommu/arm-smmu: Add tlb_sync implementation hook

>> +	for (i = 0; i < to_nsmmu(smmu)->num_inst; i++)

>It might make more sense to make this the innermost loop, i.e.:
	for (i = 0; i < nsmmu->num_inst; i++)
		reg &= readl_relaxed(nsmmu_page(smmu, i, page)...
>since polling the instances in parallel rather than in series seems like it might be a bit more efficient.

Sync register is programmed at the same time for both instances. The status check is serialized.
I can update it to check status of both at the same time.

>> +	if (smmu->impl->tlb_sync) {
>> +		smmu->impl->tlb_sync(smmu, page, sync, status);

>What I'd hoped is that rather than needing a hook for this, you could just override smmu_domain->tlb_ops from .init_context to wire up the alternate .sync method directly. That would save this extra level of indirection.

With arm_smmu_domain now available in arm-smmu.h,  arm-smmu-nvidia.c can directly update the tlb_ops->tlb_sync and avoid indirection.
Will update in next version.

-KR