[PATCH 0/3] drm/mst: Add support for simultaneous down replies

[Lyude Paul]

On Thu, 2020-02-13 at 16:15 -0500, Sean Paul wrote:
> From: Sean Paul <seanpaul at chromium.org>
> 
> Hey all,
> Earlier this week on my 5.5 kernel (I can't seem to get a 5.6 kernel to
> behave on any of my devices), I ran into the multi-reply problem that
> Wayne fixed in January. Without realizing there was already a fix
> upstream, I went about solving it in different way. It wasn't until
> rebasing the patches on 5.6 for the list that I realized there was
> already a solution.
> 
> At any rate, I think this way of handling things might be a bit more
> performant. I'm not super happy with the cleanliness of the code, I
> think this series should make things easier to read, but I don't think I
> achieved that. So suggestions are welcome on how to break this apart.

Honestly it looks a bit cleaner to me. Sideband message parsing in MST is
pretty complex, so I'd think the code's probably always going to be messy to
some extent.

My only suggestion with cleaning things up - maybe we should stop calling it
building a sideband reply, and call it re-assembling one? Seems a little less
confusing, since we're really just taking the rx chunks and reassembling them
into a full sideband message. I know at least I constantly find myself
forgetting those functions are for rx and not tx.

So, I will give my r-b for the whole series, but...

Reviewed-by: Lyude Paul <lyude at redhat.com>

...I think we should definitely look more into what Wayne's talking about
before pushing this, and see if it's widespread enough of an issue to be a
concern. It does kind of suck how slow MST probing can be, so I'd wonder if we
could try your idea of rate limiting. My one concern there is I'm not actually
sure if there's anything in the DP MST protocol that indicates how many
messages a hub can handle at the same time - it's always supposed to just be
two iirc.

> Thanks,
> 
> Sean
> 
> Sean Paul (3):
>   drm/mst: Separate sideband packet header parsing from message building
>   drm/mst: Support simultaneous down replies
>   drm/dp_mst: Remove single tx msg restriction.
> 
>  drivers/gpu/drm/drm_dp_mst_topology.c | 196 ++++++++++++++------------
>  include/drm/drm_dp_mst_helper.h       |  65 ++++-----
>  2 files changed, 137 insertions(+), 124 deletions(-)
> 
-- 
Cheers,
	Lyude Paul (she/her)
	Associate Software Engineer at Red Hat