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

[Mark Millard]

On 2020-Sep-20, at 14:04, Klaus Cucinauomo <maciphone2 at googlemail.com> wrote:
> 
>> Am 20.09.2020 um 22:33 schrieb Mark Millard <marklmi at yahoo.com>:
>> 
>> "OpenBSD can deal with the 3GB limit.  In fact it imposes a 1GB DMA limit because there are additional DMA restrictions for the SD controller." ( Mark Kettenis Aug 24, 2020; 4:29am Re: Discuss UEFI settingsin arm64.html/INSTALL.arm64 )
>> 
>> 
> —— Mark Kettenis Thu, 16 Apr 2020 14:06:19 -0700 :---
> Still thinking about the best approach to deal with this.  There is a
> 1GB limit as well for the "GPU" devices such as the USB 2.0 and SDHC
> controllers.  So it's either setting the DMA constraint to 3GB and
> adding a bounce buffer implementation, or setting the DMA constraint
> to 1GB.
> —---

So OpenBSD seems to have one, global "DMA constraint" available and
if the smallest figure is not used as the global figure, the more
restricted contexts have extra work to do to meet their own
constraints (bounce buffer use above).

That certainly helps explain the quote that I gave. Thanks.

> Well, Mark(Millard:-) ,
> 
> there seems to be a magician in the background and I don’t know why 
> but that guy is always exactly following „my“  „instructions" :-)  Ha Ha, lol awesome :
> .. here we go: ------
> https://reviews.freebsd.org/D26493
> https://reviews.freebsd.org/D26494
> https://reviews.freebsd.org/D26495
> https://reviews.freebsd.org/D26496
> ..
> https://reviews.freebsd.org/rS365929
> ..

Cool.

===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)