Commen=
t # 18
on bug 98897<=
/a>
from berg
(In reply to C=C3=A9dric Le Goater from comment #17)
> so this is a CHIP_VERDE revision 0x83
(In reply to C=C3=A9dric Le Goater from comment #14)
> (In reply to Michel D=C3=A4nzer from comment #10)
> > If you can't or don't want to bisect, there are only 4 radeon dri=
ver commits
> > between 4.8.6 and 4.8.7, so it shouldn't take long to try manuall=
y reverting
> > each of those.
> > https://git.kernel.org/cgit/linux/kernel/git/stable=
/linux-stable.git/commit/
> > ?h=3Dlinux-4.8.y&id=3De136de5d733161fdfd203f23b448434170d189e=
a seems like a good
> > candidate, since it's clock related and explicitly references you=
r GPU in
> > the code.
>=20
> Hi,
>=20
> I have reverted this commit on a 4.8.14 and the flickering stopped.
>=20
> C.
Having a looking at the diff; the new diff actually configures=20
} else if (rdev->family =3D=3D CHIP_VERDE) {
+ if ((rdev->pdev->revision =3D=3D 0x81) ||
+ (rdev->pdev->revision =3D=3D 0x83) ||
...
+ (rdev->pdev->device =3D=3D 0x6821) ||
...
+ (rdev->pdev->device =3D=3D 0x682B)) {
+ max_sclk =3D 75000;
+ max_mclk =3D 80000;
+ }
So on my MacBook Pro 11,5 - the device ID and revision are:=20
01:00.0 0300: 1002:6821 (rev 83)
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
Venus XT [Radeon HD 8870M / R9 M270X/M370X] (rev 83)
So; since this commit, the max_sclk and max_mclk has been set for this GPU =
to
75000 and 80000. In previous version of this driver module, this specific G=
PU
was being skipped. I think these values have been incorrectly set for this =
CPU.
According to these specifications for the M370X Mac chip,
http://gpu=
boss.com/graphics-card/Radeon-R9-M370X-Mac, the two values max_sclk
and max_mclk are probably:
Clock speed 775 MHz
Turbo clock speed 800 MHz
So we are setting this stuff to run possibly 25 MHz out of sync with the ac=
tual
GPU clock. I'm guessing this would be subtle enough to cause the flickering
we're seeing, perhaps it should be something like this:
} else if (rdev->family =3D=3D CHIP_VERDE) {
if (rdev->pdev->device =3D=3D 0x6821 &&
rdev->pdev->revision =3D=3D 0x83) {
max_sclk =3D 77500;
max_mclk =3D 80000;
} else if other conditions
In general though, the new block of device and revisions are VERY loose and=
not
very well thought out. The OR conditionals are too far reaching. This GPU is
matched in two different sections and even the device ID or the revision al=
one
is enough to modify the aforementioned values.
I might make compile 4.9.0 tonight to try this theory out and set max_sclk =
to
77500. Perhaps the best actual solution is to not even include this device =
and
revision in the dpm quirks; as it was previously omitted and was never an
actual problem.
I haven't figured out how to determine the actual GPU frequency right now, =
but
if we can confirm it's running at a stock speed of 775 MHz, that would give=
me
greater confidence in testing this idea out.