busdma problem

[Andrew Thompson]

On Fri, Jan 30, 2009 at 09:31:47AM -0800, Andrew Thompson wrote:
> On Fri, Jan 30, 2009 at 09:18:11AM -0800, Sam Leffler wrote:
> > Andrew Thompson wrote:
> >> Hi,
> >> 
> >> 
> >> I am having an issue with busdma when bounce buffers are used. I have
> >> patched _bus_dmamap_sync_bp() to print out the details when a bounce
> >> happens and also print the driver buffer before and after.
> >> 
> >> During normal dma everything is fine,
> >> 
> >> Before: 0xc7c1ab40 data=c1:4b:a4:80:c0:5d:ed:78:00:00:08:0d:c1:1f:46:78:00:00:20:02:00:00:20:02:
> >> [...do dma...]
> >> After:  0xc7c1ab40 data=2c:03:4e:00:6f:00:76:00:61:00:74:00:65:00:6c:00:20:00:57:00:69:00:72:00:
> >> 
> >> The buffer 2c:03:4e:00:... is the correct response from the hardware.
> >> When a bounce buffer is used I see the correct data come in and be
> >> bcopy'd to my memory region but it is not visible when read later.
> >> 
> >> Before: 0xc7c29b40 data=c1:50:19:00:c0:5d:ed:f8:00:00:08:0d:c1:1f:46:78:00:00:20:02:00:00:20:02:
> >> dma bounced 0x1271000 -> 0xc7c29b40 len=193 data=2c:03:4e:00:6f:00:76:00:61:00:74:00:65:00:6c:00:20:00:57:00:69:00:72:00:
> >> After:  0xc7c29b40 data=c1:50:19:00:c0:5d:ed:f8:00:00:08:0d:c1:1f:46:78:00:00:20:02:00:00:20:02:
> >> 
> >> 
> >> This is on an xscale ixp425 with 128m memory, the PCI dma tag is limited
> >> to 64m.
> >>   
> > What device is involved?  Is this on HEAD?
> 
> This is usb/ehci. The specific function I am looking at is
> usbd_get_string() in usbdi.c, it does a usb request to fill
> usb_string_descriptor_t that is a stack variable.

As suggested by Sam, this works properly when the buffer is malloc'd
instead of taken from the stack. So is this now a bug or a feature??


Andrew