Comment #135 for bugzilla 237666 : a USB3-handling problem with a investigatory fix for a cortex-a72 context

[Klaus Cucinauomo]

> Am 20.09.2020 um 03:32 schrieb Mark Millard <marklmi at yahoo.com>:
> 
> ...So: unrelated fixes. ...

> For the u-boot context, my guess is that the patch that
> restricted the size of the DMA region to 1 GiByte or so
> to allow things to progress there is effectively a work
> around that avoids touching another bug(s) some place.
> (NetBSD and Linux do not have such a small size limit.
> OpenBSD choose its small limit for other reasons.)


Ah, O.K., thanks, got it...

..the bug is that dma of 1GB is always safe but there is no "OS-pre-implementation" 
for 3GB buffer in 64-bit for RPI4… while , the pcie-device itself DOESN`t have the 
1GB - limit like other peripherals..
..
NetBSD also did it that (OpenBSD-)way at first , not for other but the same reason, 
I GUESS(!).. while , as you know,guessing(and dma) isn't really my area of expertise ;-) :

https://github.com/NetBSD/src/commit/5cb936da2a4720fa51984394998fa62c62aea7cd#diff-8e16a107fed72481ef0342727619cfa8  :

#define BCM2711_DMA_SIZE	0x3c000000 …,( which is 1GB)

jmcneill seems to have then added some voodoo in NetBSD :
https://github.com/NetBSD/src/commit/9bf4ec11d132c8b296a3926483aa0b8d43fa43ad

the Tux has fixed it there :
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/arm64/iort.c?h=v5.8&id=bcf876870b95592b52519ed4aafcf9d95999bc9c#n1125
..they have things like dma_zone or so...

So hardcoding the 1GB constraint into https://reviews.freebsd.org/D25219 
or
give it a fine grain dma range to 3GB should fix it...

Since you teamed up with HPS you both now exactly know what to do,
please fix it(today of course:-).. 
(finally yet another flat joke )

Regards