[PATCH 18/20] drm/amd/display: Verify disallow bits were cleared for idle

[Rodrigo Siqueira]

From: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>

[Why]
A hang was observed where a read-modify-write access occurred due to the
register for idle state being shared between DMCUB and driver.

dmcub read - idle allow / no commit
driver read - idle allow / no commit
driver write - idle disallow / no commit
dmcub write - idle allow / commit

Resulting in DMCUB re-entering IPS after a disable and keeping the allow
high.

[How]
Long term we need to split commit/allow into two registers or use shared
DRAM state, but short term we can reduce the repro rate by ensuring that
the disallow went through by bounding the expected worst case scenario.

Reviewed-by: Hansen Dsouza <hansen.dsouza at amd.com>
Reviewed-by: Ovidiu Bunea <ovidiu.bunea at amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira at amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
---
 drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c b/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
index dadeaa9c92dd..a65c485b0b49 100644
--- a/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
+++ b/drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
@@ -1233,8 +1233,16 @@ static void dc_dmub_srv_exit_low_power_state(const struct dc *dc)
 
 		if (!(allow_state & DMUB_IPS2_ALLOW_MASK)) {
 			// Wait for evaluation time
-			udelay(dc->debug.ips2_eval_delay_us);
-			commit_state = dc->hwss.get_idle_state(dc);
+			for (;;) {
+				udelay(dc->debug.ips2_eval_delay_us);
+				commit_state = dc->hwss.get_idle_state(dc);
+				if (commit_state & DMUB_IPS2_ALLOW_MASK)
+					break;
+
+				/* allow was still set, retry eval delay */
+				dc->hwss.set_idle_state(dc, false);
+			}
+
 			if (!(commit_state & DMUB_IPS2_COMMIT_MASK)) {
 				// Tell PMFW to exit low power state
 				dc->clk_mgr->funcs->exit_low_power_state(dc->clk_mgr);
-- 
2.42.0