[PATCH] drm/mgag200: Increase bandwidth for G200se A rev1

[Roger Sewell]

Jocelyn, Thomas,

JF> I think the culprit is probably this patch:
JF> https://patchwork.freedesktop.org/patch/486242/
JF> 
JF> before this patch,
JF> mgag200_simple_display_pipe_mode_valid() always return MODE_OK
JF> 
JF> after this patch, it checks the bandwidth limit too.

I can easily test this theory, which sounds entirely reasonable - I will
do so and let you know the result.

TZ> I'm not quite sure how to proceed here, as the driver is correct and
TZ> the problem came from a mismatching config file on your system.

In so far as a user's viewpoint is relevant, I would say this: 

A user wants to be able to obtain any mode that actually is usable with
his hardware. He starts from a position of not having any extra config
files in place, and it works. He wants a different mode, so he adds a
config file. If he does that deliberately, then the system should allow
it, even if it goes over some theoretical limit - as if he gets no
video, he will then know exactly why he got no video (and can use the
tty interface after a reboot to remove his config file). (But by all
means put a warning message in the logs.)

What is really bad is for a mode that used to work to stop working with
no explanation - and even to stop working in such a manner that the only
way to get the system back is to force a reboot by removing power rather
than defaulting to a different mode. (But I think that that behaviour
results from userspace not expecting a late rejection of the mode.)

Moreover, any decent system that uses a GUI to allow you to change
screen mode offers you a preview before locking that mode in - and
automatically reverses the change if the user doesn't confirm it.

So I would prefer a mode chosen by a deliberate xorg config file to not
be rejectable by the driver, but just give a warning in the logs.

(But I do understand that you will also need to consider other points of
view.)

I'll confirm the result of the above test shortly.

Thanks,
Roger.