linux-kernel - Re: [PATCH v2 04/17] driver core: platform: Add driver dma ownership management

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Date:   Sun, 28 Nov 2021 09:10:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        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>, iommu@...ts.linux-foundation.org,
        linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 04/17] driver core: platform: Add driver dma ownership
 management

On Sun, Nov 28, 2021 at 10:50:38AM +0800, Lu Baolu wrote:
> Multiple platform devices may be placed in the same IOMMU group because
> they cannot be isolated from each other. These devices must either be
> entirely under kernel control or userspace control, never a mixture. This
> checks and sets DMA ownership during driver binding, and release the
> ownership during driver unbinding.
> 
> Driver may set a new flag (suppress_auto_claim_dma_owner) to disable auto
> claiming DMA_OWNER_DMA_API ownership in the binding process. For instance,
> the userspace framework drivers (vfio etc.) which need to manually claim
> DMA_OWNER_PRIVATE_DOMAIN_USER when assigning a device to userspace.

Why would any vfio driver be a platform driver?  That should never be
the case as they obviously are not platform drivers, they are virtual
ones.

> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  include/linux/platform_device.h |  1 +
>  drivers/base/platform.c         | 30 +++++++++++++++++++++++++++++-
>  2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index 7c96f169d274..779bcf2a851c 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -210,6 +210,7 @@ struct platform_driver {
>  	struct device_driver driver;
>  	const struct platform_device_id *id_table;
>  	bool prevent_deferred_probe;
> +	bool suppress_auto_claim_dma_owner;

What platform driver needs this change?

>  };
>  
>  #define to_platform_driver(drv)	(container_of((drv), struct platform_driver, \
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 598acf93a360..df4b385c8a52 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -30,6 +30,7 @@
>  #include <linux/property.h>
>  #include <linux/kmemleak.h>
>  #include <linux/types.h>
> +#include <linux/iommu.h>
>  
>  #include "base.h"
>  #include "power/power.h"
> @@ -1465,6 +1466,32 @@ int platform_dma_configure(struct device *dev)
>  	return ret;
>  }
>  
> +static int _platform_dma_configure(struct device *dev)
> +{
> +	struct platform_driver *drv = to_platform_driver(dev->driver);
> +	int ret;
> +
> +	if (!drv->suppress_auto_claim_dma_owner) {
> +		ret = iommu_device_set_dma_owner(dev, DMA_OWNER_DMA_API, NULL);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	ret = platform_dma_configure(dev);
> +	if (ret && !drv->suppress_auto_claim_dma_owner)
> +		iommu_device_release_dma_owner(dev, DMA_OWNER_DMA_API);
> +
> +	return ret;
> +}
> +
> +static void _platform_dma_unconfigure(struct device *dev)
> +{
> +	struct platform_driver *drv = to_platform_driver(dev->driver);
> +
> +	if (!drv->suppress_auto_claim_dma_owner)
> +		iommu_device_release_dma_owner(dev, DMA_OWNER_DMA_API);
> +}
> +
>  static const struct dev_pm_ops platform_dev_pm_ops = {
>  	SET_RUNTIME_PM_OPS(pm_generic_runtime_suspend, pm_generic_runtime_resume, NULL)
>  	USE_PLATFORM_PM_SLEEP_OPS
> @@ -1478,7 +1505,8 @@ struct bus_type platform_bus_type = {
>  	.probe		= platform_probe,
>  	.remove		= platform_remove,
>  	.shutdown	= platform_shutdown,
> -	.dma_configure	= platform_dma_configure,
> +	.dma_configure	= _platform_dma_configure,

What happened to the original platform_dma_configure() function?

And single "_" prefixes are odd, please just spell out what the
difference is in the function name, "_" gives us no hint at all.

thnaks,

greg k-h