[PATCH 3/3] dma-mapping: introduce DMA range map, supplanting dma_pfn_offset

Greg KH greg at kroah.com
Thu Sep 10 03:53:51 EDT 2020

On Thu, Sep 10, 2020 at 07:40:38AM +0200, Christoph Hellwig wrote:
> From: Jim Quinlan <james.quinlan at broadcom.com>
> The new field 'dma_range_map' in struct device is used to facilitate the
> use of single or multiple offsets between mapping regions of cpu addrs and
> dma addrs.  It subsumes the role of "dev->dma_pfn_offset" which was only
> capable of holding a single uniform offset and had no region bounds
> checking.
> The function of_dma_get_range() has been modified so that it takes a single
> argument -- the device node -- and returns a map, NULL, or an error code.
> The map is an array that holds the information regarding the DMA regions.
> Each range entry contains the address offset, the cpu_start address, the
> dma_start address, and the size of the region.
> of_dma_configure() is the typical manner to set range offsets but there are
> a number of ad hoc assignments to "dev->dma_pfn_offset" in the kernel
> driver code.  These cases now invoke the function
> dma_attach_offset_range(dev, cpu_addr, dma_addr, size).

So if an error happens, we don't do anything?

> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index 6197938dcc2d8f..935ee98e049f65 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -1956,10 +1956,11 @@ int usb_set_configuration(struct usb_device *dev, int configuration)
>  		intf->dev.groups = usb_interface_groups;
>  		/*
>  		 * Please refer to usb_alloc_dev() to see why we set
> -		 * dma_mask and dma_pfn_offset.
> +		 * dma_mask and dma_range_map.
>  		 */
>  		intf->dev.dma_mask = dev->dev.dma_mask;
> -		intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset;
> +		if (dma_direct_copy_range_map(&intf->dev, &dev->dev))
> +			dev_err(&dev->dev, "failed to copy DMA map\n");

We tell the user, but then just keep on running?  Is there anything that
we can do here?

If not, why not have dma_direct_copy_range_map() print out the error?


greg k-h

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