The DC_STATE_EN register has read-only status bits that are set by hardware on some platforms. These bits may cause the read-back verification loop in gen9_write_dc_state() to spuriously retry.
Mask the RO bits from the read-back comparison to prevent unnecessary retries. Changes in v2: - Rename patch from "drm/i915/display: Use rmw in gen9_write_dc_state() to preserve non-DC bits" to "drm/i915/display: Mask RO bits in gen9_write_dc_state()" - Mask only RO bits rather than masking all non DC state bits in DC_STATE_EN. As the register has also some clear-on-write flags, like 'Display DC*CO State Status DSI'(Imre Deak) Changes in v3: - Limit ro mask to read-back comparison. BSpec: 49437,69115 Signed-off-by: Dibin Moolakadan Subrahmanian <[email protected]> --- .../i915/display/intel_display_power_well.c | 24 +++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/display/intel_display_power_well.c b/drivers/gpu/drm/i915/display/intel_display_power_well.c index 04bd0dde5bed..ab0200701a73 100644 --- a/drivers/gpu/drm/i915/display/intel_display_power_well.c +++ b/drivers/gpu/drm/i915/display/intel_display_power_well.c @@ -726,12 +726,28 @@ static void assert_can_disable_dc9(struct intel_display *display) */ } +static u32 dc_state_ro_mask(struct intel_display *display) +{ + if (DISPLAY_VER(display) >= 20) + return BIT(10) | BIT(11); + else if (DISPLAY_VER(display) >= 13 && !display->platform.dg2) + return BIT(10); + + return 0; +} + static void gen9_write_dc_state(struct intel_display *display, u32 state) { int rewrites = 0; int rereads = 0; u32 v; + /* + * Mask out RO status bits from read-back comparison. + * HW may set these bits independently, so exclude them + * to prevent the verify loop from retrying due to RO bits mismatch. + */ + u32 ro_mask = dc_state_ro_mask(display); intel_de_write(display, DC_STATE_EN, state); @@ -743,7 +759,7 @@ static void gen9_write_dc_state(struct intel_display *display, do { v = intel_de_read(display, DC_STATE_EN); - if (v != state) { + if ((v & ~ro_mask) != (state & ~ro_mask)) { intel_de_write(display, DC_STATE_EN, state); rewrites++; rereads = 0; @@ -753,10 +769,10 @@ static void gen9_write_dc_state(struct intel_display *display, } while (rewrites < 100); - if (v != state) + if ((v & ~ro_mask) != (state & ~ro_mask)) drm_err(display->drm, - "Writing dc state to 0x%x failed, now 0x%x\n", - state, v); + "Writing dc state to 0x%x failed, now 0x%x (ro_mask=0x%x)\n", + state, v, ro_mask); /* Most of the times we need one retry, avoid spam */ if (rewrites > 1) -- 2.43.0
