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drm/amd/display: Verify disallow bits were cleared for idle

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[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.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Hansen Dsouza <hansen.dsouza@amd.com>
Reviewed-by: Ovidiu Bunea <ovidiu.bunea@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Nicholas Kazlauskas
2023-12-14 16:46:35 -05:00
committed by Alex Deucher
parent 9ade4870b8
commit b8a204fb1a
1 changed files with 10 additions and 2 deletions
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12
drivers/gpu/drm/amd/display/dc/dc_dmub_srv.c
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@@ -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);