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

From: Greg KH
Date: Thu Sep 10 2020 - 03:54:06 EST

On Thu, Sep 10, 2020 at 07:40:38AM +0200, Christoph Hellwig wrote:
> From: Jim Quinlan <james.quinlan@xxxxxxxxxxxx>
> 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