On Fri, 27 Aug 2021 at 10:14, Mark Cave-Ayland
<mark.cave-ayland@ilande.co.uk> wrote:
Ah so the plan moving forward is to always have an explicit MR passed in for
DMA use.
Sorry if I missed that in earlier versions of the patchset, I'm still getting
back up
to speed on QEMU hacking.
Was there a decision as to what the property name should be? I see "dma_mr" used
quite a bit, and if there will be more patches to remove the system_memory
default
from other devices then it would be nice to try and use the same name
everywhere.
No, I don't think we have a convention; it might be nice to add one.
Currently a quick git grep for DEFINE_PROP_LINK and eyeballing of
the results shows that we have:
"memory" x 7
"dram" x 4
"downstream" x 3
"dma-memory" x 3
"dma" x 2
"source-memory"
"dram-mr"
"ddr"
"ddr-ram"
"gic"
"cpc"
"port[N]"
"dma_mr"
"ahb-bus"
"system-memory"
"main-bus"
This list includes all our TYPE_MEMORY_REGION link properties; a few of these
are special-purpose, and reasonably have specialized names. 2 out of 3 users
of "downstream" are devices which pass on (or filter out) memory transactions
from the CPU (tz-msc, tz-mpc), and I think that name makes sense there.
(The 3rd is pl080.c, which is a plain old DMA controller, and the naming
there is not so well-suited.)
"memory" is mostly SoC and CPU objects taking a link to whatever they should
have as the CPU's view of memory.
I don't have a strong view on what we ought to try to standardize on,
except that I don't like the "_mr" or "-mr" suffix -- I don't think we
need to try to encode the type of the link property in the property name.
It is probably reasonable to have different naming conventions for:
* SoC and CPU objects, which take a link to the MR which represents
the CPU/SoC's view of the outside world
* Endpoint devices which can be DMA masters and take a link giving
them their view of what they can DMA to
* filtering/control devices which take incoming transactions from
an upstream port, filter some and pass the rest through to a
downstream port
In pretty much all cases, these link properties are used only internally
to QEMU, so if we decide on a naming convention we can fairly easily
rename existing properties to match.