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

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Message-ID: <3d734164-51c9-3465-cddd-276093389797@arm.com>
Date:   Mon, 2 Sep 2019 14:00:07 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Krishna Reddy <vdumpa@...dia.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

On 30/08/2019 23:49, Krishna Reddy wrote:
>>> +	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.
> 
> Hi Robin,  overriding tlb_ops->tlb_sync function is not enough here.
> There are direct references to arm_smmu_tlb_sync_context(),  arm_smmu_tlb_sync_global() functions.
> In arm-smmu.c.  we can replace these direct references with tlb_ops->tlb_sync() function except in one function arm_smmu_device_reset().
> When arm_smmu_device_reset() gets called, domains are not initialized and tlb_ops is not available.
> Should we add a new hook for arm_smmu_tlb_sync_global() or make this as a responsibility of impl->reset() hook as it gets
> called at the same place?

Ah, right, I'd forgotten about the TLB maintenance on reset. Looking 
again, though, I think you might need to implement impl->reset anyway 
for the sake of clearing GFSR correctly - since the value read from the 
base instance technically may not match whatever bits might happen to be 
set in the other instances - so I don't see any issue with just calling 
nsmmu_tlb_sync() from there as well.

Robin.