linux-kernel - Re: [RFC PATCH 1/3] dma-mapping: introduce a new dma api dma_addr_to_phys

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Date:   Thu, 24 Oct 2019 07:49:03 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     "hch@....de" <hch@....de>
CC:     Robin Murphy <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Leo Li <leoyang.li@....com>,
        Diana Madalina Craciun <diana.craciun@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Madalin Bucur <madalin.bucur@....com>
Subject: Re: [RFC PATCH 1/3] dma-mapping: introduce a new dma api
 dma_addr_to_phys_addr()



On 24.10.2019 05:01, hch@....de wrote:
> On Wed, Oct 23, 2019 at 11:53:41AM +0000, Laurentiu Tudor wrote:
>> We had an internal discussion over these points you are raising and
>> Madalin (cc-ed) came up with another idea: instead of adding this prone
>> to misuse api how about experimenting with a new dma unmap and dma sync
>> variants that would return the physical address by calling the newly
>> introduced dma map op. Something along these lines:
>>    * phys_addr_t dma_unmap_page_ret_phys(...)
>>    * phys_addr_t dma_unmap_single_ret_phys(...)
>>    * phys_addr_t dma_sync_single_for_cpu_ret_phys(...)
>> I'm thinking that this proposal should reduce the risks opened by the
>> initial variant.
>> Please let me know what you think.
> 
> I'm not sure what the ret is supposed to mean, but I generally like
> that idea better.  

It was supposed to be short for "return" but given that I'm not good at 
naming stuff I'll just drop it.

> We also need to make sure there is an easy way
> to figure out if these APIs are available, as they generally aren't
> for any non-IOMMU API IOMMU drivers.

I was really hoping to manage making them as generic as possible but 
anyway, I'll start working on a PoC and see how it turns out. This will 
probably happen sometime next next week as the following week I'll be 
traveling to a conference.

---
Best Regards, Laurentiu