drm/radeon/kms: read back register before writing in IIO.
This fixes RH bugzilla #527874.
On resume the atom posting wasn't working, however vbe posting was
going fine, after 2 weeks over irc, and 8 hrs with the hardware,
I tracked it down to the memory device table and it access the MC
registers via IIO, it appears the rv515 atom iio table might not
be fully functional, so adding a readback before doing a write
either provides enough delay to make things resume correctly.
Thanks to Peng Huang at Red Hat for coming to Brisbane.
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/atom.c b/drivers/gpu/drm/radeon/atom.c
index 901befe..d67c425 100644
--- a/drivers/gpu/drm/radeon/atom.c
+++ b/drivers/gpu/drm/radeon/atom.c
@@ -107,6 +107,7 @@
base += 3;
break;
case ATOM_IIO_WRITE:
+ (void)ctx->card->reg_read(ctx->card, CU16(base + 1));
ctx->card->reg_write(ctx->card, CU16(base + 1), temp);
base += 3;
break;