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 901befe03da278e7a6879c9cab1498a315eb0248..d67c42555ab9b826b4f18a7a91fa30e02b2522ae 100644 (file)
--- a/drivers/gpu/drm/radeon/atom.c
+++ b/drivers/gpu/drm/radeon/atom.c
@@ -107,6 +107,7 @@ static uint32_t atom_iio_execute(struct atom_context *ctx, int base,
                        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;