linux-kernel - Re: [PATCH v5 02/14] driver core: Add dma_cleanup callback in bus

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Date:   Tue, 8 Feb 2022 13:55:29 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Christoph Hellwig <hch@...radead.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 02/14] driver core: Add dma_cleanup callback in
 bus_type

Hi Greg,

On 1/4/22 9:04 PM, Greg Kroah-Hartman wrote:
> On Tue, Jan 04, 2022 at 08:39:11AM -0400, Jason Gunthorpe wrote:
>> On Tue, Jan 04, 2022 at 02:08:36AM -0800, Christoph Hellwig wrote:
>>> All these bus callouts still looks horrible and just create tons of
>>> boilerplate code.
>>
>> Yes, Lu - Greg asked questions then didn't respond to their answers
>> meaning he accepts them, you should stick with the v4 version.
> 
> Trying to catch up on emails from the break, that was way down my list
> of things to get back to as it's messy and non-obvious.  I'll revisit it
> again after 5.17-rc1 is out, this is too late for that merge window
> anyway.

In this series we want to add calls into the iommu subsystem during
device driver binding/unbinding, so that the device DMA ownership
conflict (kernel driver vs. user-space) could be detected and avoided
before calling into device driver's .probe().

In this v5 series, we implemented this in the affected buses (amba/
platform/fsl-mc/pci) which are known to support assigning devices to
user space through the vfio framework currently. And more buses are
possible to be affected in the future if they also want to support
device assignment. Christoph commented that this will create boilerplate
code in various bus drivers.

Back to v4 of this series (please refer to below link [1]), we added
this call in the driver core if buses have provided the dma_configure()
callback (please refer to below link [2]).

Which would you prefer, or any other suggestions? We need your guide to
move this series ahead. Please help to suggest.

[1] 
https://lore.kernel.org/linux-iommu/20211217063708.1740334-1-baolu.lu@linux.intel.com/
[2] 
https://lore.kernel.org/linux-iommu/20211217063708.1740334-3-baolu.lu@linux.intel.com/

Best regards,
baolu