linux-kernel - Re: [PATCH v5 04/14] driver core: platform: Add driver dma ownership management

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Message-ID: <YgooFjSWLTSapuIs@kroah.com>
Date:   Mon, 14 Feb 2022 10:59:50 +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>,
        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 04/14] driver core: platform: Add driver dma ownership
 management

On Tue, Jan 04, 2022 at 09:56:34AM +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.
> 
> The device driver may set a new flag (no_kernel_api_dma) to skip calling
> iommu_device_use_dma_api() during the binding process. For instance, the
> userspace framework drivers (vfio etc.) which need to manually claim
> their own dma ownership when assigning the device to userspace.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  include/linux/platform_device.h |  1 +
>  drivers/base/platform.c         | 20 ++++++++++++++++++++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index 17fde717df68..8f0eaafcef47 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 no_kernel_api_dma;
>  };
>  
>  #define to_platform_driver(drv)	(container_of((drv), struct platform_driver, \
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index b4d36b46ab2e..d5171e44d903 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"
> @@ -1451,9 +1452,16 @@ static void platform_shutdown(struct device *_dev)
>  
>  static int platform_dma_configure(struct device *dev)
>  {
> +	struct platform_driver *drv = to_platform_driver(dev->driver);
>  	enum dev_dma_attr attr;
>  	int ret = 0;
>  
> +	if (!drv->no_kernel_api_dma) {
> +		ret = iommu_device_use_dma_api(dev);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	if (dev->of_node) {
>  		ret = of_dma_configure(dev, dev->of_node, true);
>  	} else if (has_acpi_companion(dev)) {
> @@ -1461,9 +1469,20 @@ static int platform_dma_configure(struct device *dev)
>  		ret = acpi_dma_configure(dev, attr);
>  	}
>  
> +	if (ret && !drv->no_kernel_api_dma)
> +		iommu_device_unuse_dma_api(dev);

So you are now going to call this for every platform driver _unless_
they set this flag?

And having "negative" flags is rough to parse at times.  Yes, we have
"prevent_deferred_probe" already here, so maybe keep this in the same
nameing scheme and use "prevent_dma_api"?

And it would be good to document this somewhere as to what this means.

thanks,

greg k-h