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

[Greg Kroah-Hartman]

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@xxxxxxxxxxxxxxx>
> ---
>  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