linux-kernel - Re: [PATCH V11 3/5] i2c: tegra: Add DMA support

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 6 Feb 2019 20:37:36 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>
Cc:     jonathanh@...dia.com, mkarthik@...dia.com, smohammed@...dia.com,
        talho@...dia.com, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH V11 3/5] i2c: tegra: Add DMA support

06.02.2019 17:56, Dmitry Osipenko пишет:
> 06.02.2019 17:53, Thierry Reding пишет:
>> On Tue, Feb 05, 2019 at 05:26:25PM +0300, Dmitry Osipenko wrote:
>> [...]
>>> Oh, another important moment is that physically contiguous dma_buf
>>> allocation isn't guaranteed by the DMA API. This may become a problem
>>> for T186+ that can transfer up to 64K. We need to enforce the
>>> contiguous-allocation requirement by using
>>> dma_alloc_attrs(DMA_ATTR_FORCE_CONTIGUOUS) instead of the
>>> dma_alloc_coherent(), please see my other comment below.
>>
>> Actually I don't think that's necessary here. DMA_ATTR_FORCE_CONTIGUOUS
>> only seems relevant if you've got an IOMMU attached to the device to
>> make sure the physical memory is also contiguous.
>>
>> See this extract from Documentation/DMA-attributes.txt:
>>
>> | DMA_ATTR_FORCE_CONTIGUOUS
>> | -------------------------
>> | 
>> | By default DMA-mapping subsystem is allowed to assemble the buffer
>> | allocated by dma_alloc_attrs() function from individual pages if it can
>> | be mapped as contiguous chunk into device dma address space. By
>> | specifying this attribute the allocated buffer is forced to be contiguous
>> | also in physical memory.
>>
>> We don't have an IOMMU attached to I2C or APBDMA, so this can't happen
>> and even if we had an IOMMU attached, all we care about is the device's
>> DMA address space, which means IOVA space, and that would still be
>> guaranteed to be contiguous, according to the above.
> 
> Yes, but doesn't T186+ have IOMMU support for the DMA controller?
> 

Ah, sorry I probably skimmed way too quickly thorough the message. Hmm.. well, seems I was wrong.

Sowjanya, after all looks like it should be fine to use the default dma_alloc_coherent() helper. Please put it back in v14.