linux-kernel - Re: [PATCH v3 04/18] driver core: platform: Add driver dma ownership management

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Date:   Mon, 6 Dec 2021 11:06:47 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.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 v3 04/18] driver core: platform: Add driver dma ownership
 management

On Mon, Dec 06, 2021 at 06:36:27AM -0800, Christoph Hellwig wrote:
> I really hate the amount of boilerplate code that having this in each
> bus type causes.

+1 

I liked the first version of this series better with the code near
really_probe().

Can we go back to that with some device_configure_dma() wrapper
condtionally called by really_probe as we discussed?

> Between that and the suggestion from Joerg I wonder if we could do the
> following again:
> 
>  - add new no_kernel_dma flag to struct device_driver
>  - set this flag for the various vfio drivers
>  - skip claiming the kernel dma ownership for those (or rather release
>    it if the suggestion from Joerg works out)

v1 did exactly this.

Jason