linux-kernel - Re: [PATCH v6 6/6] iommu/tegra-smmu: Add pagetable mappings to debugfs

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Date:   Tue, 14 Sep 2021 22:20:30 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     thierry.reding@...il.com, joro@...tes.org, will@...nel.org,
        vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 6/6] iommu/tegra-smmu: Add pagetable mappings to
 debugfs

14.09.2021 21:49, Nicolin Chen пишет:
> On Tue, Sep 14, 2021 at 04:29:15PM +0300, Dmitry Osipenko wrote:
>> 14.09.2021 04:38, Nicolin Chen пишет:
>>> +static unsigned long pd_pt_index_iova(unsigned int pd_index, unsigned int pt_index)
>>> +{
>>> +	return ((dma_addr_t)pd_index & (SMMU_NUM_PDE - 1)) << SMMU_PDE_SHIFT |
>>> +	       ((dma_addr_t)pt_index & (SMMU_NUM_PTE - 1)) << SMMU_PTE_SHIFT;
>>> +}
>>
>> We know that IOVA is fixed to u32 for this controller. Can we avoid all
>> these dma_addr_t castings? It should make code cleaner a tad, IMO.
> 
> Tegra210 actually supports 34-bit IOVA...
> 

It doesn't. 34-bit is PA, 32-bit is VA.

Quote from T210 TRM:

"The SMMU is a centralized virtual-to-physical translation for MSS. It
maps a 32-bit virtual address to a 34-bit physical address. If the
client address is 40 bits then bits 39:32 are ignored."

Even if it supported more than 32bit, then the returned ulong is 32bit,
which doesn't make sense.