usb: add a HCD_DMA flag instead of guestimating DMA capabilities

The usb core is the only major place in the kernel that checks for
a non-NULL device dma_mask to see if a device is DMA capable.  This
is generally a bad idea, as all major busses always set up a DMA mask,
even if the device is not DMA capable - in fact bus layers like PCI
can't even know if a device is DMA capable at enumeration time.  This
leads to lots of workaround in HCD drivers, and also prevented us from
setting up a DMA mask for platform devices by default last time we
tried.

Replace this guess with an explicit HCD_DMA that is set by drivers that
appear to have DMA support.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20190816062435.881-4-hch@lst.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 0 insertions, 6 deletions

diff --git a/drivers/usb/host/sl811-hcd.c b/drivers/usb/host/sl811-hcd.c
index 5b061e599948..72a34a1eb618 100644
--- a/drivers/usb/host/sl811-hcd.c
+++ b/drivers/usb/host/sl811-hcd.c
@@ -1632,12 +1632,6 @@ sl811h_probe(struct platform_device *dev)
 	irq = ires->start;
 	irqflags = ires->flags & IRQF_TRIGGER_MASK;
 
-	/* refuse to confuse usbcore */
-	if (dev->dev.dma_mask) {
-		dev_dbg(&dev->dev, "no we won't dma\n");
-		return -EINVAL;
-	}
-
 	/* the chip may be wired for either kind of addressing */
 	addr = platform_get_resource(dev, IORESOURCE_MEM, 0);
 	data = platform_get_resource(dev, IORESOURCE_MEM, 1);