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usb: add a HCD_DMA flag instead of guestimating DMA capabilities

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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>
This commit is contained in:
Christoph Hellwig
2019-08-16 08:24:32 +02:00
committed by Greg Kroah-Hartman
parent 0709831a50
commit 7b81cb6bdd
35 changed files with 31 additions and 62 deletions
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1
include/linux/usb.h
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@@ -426,7 +426,6 @@ struct usb_bus {
struct device *sysdev; /* as seen from firmware or bus */
int busnum; /* Bus number (in order of reg) */
const char *bus_name; /* stable id (PCI slot_name etc) */
u8 uses_dma; /* Does the host controller use DMA? */
u8 uses_pio_for_control; /*
* Does the host controller use PIO
* for control transfers?