From 04d57f4462a6c39f04711550aa60c42c8ed5d25d Mon Sep 17 00:00:00 2001 From: Dominik Kaszewski Date: Tue, 24 Jun 2025 12:40:25 +0200 Subject: [PATCH] drm/amd/display: Workaround for stuck I2C arbitrage [Why] When booting without an HDMI display connected, the I2C registers are not initialized correctly, leading to DC_I2C_ARBITRATION register getting stuck with DC_I2C_REG_RW_CNTL_STATUS == USED_BY_SW. [How] * Correct TOCTOU race condition in engine acquire logic which did not check against DMUB trying to acquire it at the same time. * Deassert SOFT_RESET before acquire, as it can block access to other I2C registers. * Add a workaround in release, checking that after triggerring DC_I2C_SW_DONE_USING_I2C_REG, DC_I2C_REG_RW_CNTL_STATUS != USED_BY_SW. If necessary, trigger DC_I2C_SW_DONE_USING_I2C_REG again. * Remove unnecessary clear of DC_I2C_SW_USE_I2C_REG_REQ, which engine ignores according to specification. Reviewed-by: Alvin Lee Signed-off-by: Dominik Kaszewski Signed-off-by: Ivan Lipski Tested-by: Daniel Wheeler Signed-off-by: Alex Deucher --- .../gpu/drm/amd/display/dc/dce/dce_i2c_hw.c | 59 ++++++++++++++++--- 1 file changed, 52 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_i2c_hw.c b/drivers/gpu/drm/amd/display/dc/dce/dce_i2c_hw.c index d28826c3ae5f1..4e06468a62842 100644 --- a/drivers/gpu/drm/amd/display/dc/dce/dce_i2c_hw.c +++ b/drivers/gpu/drm/amd/display/dc/dce/dce_i2c_hw.c @@ -292,9 +292,35 @@ static void set_speed( FN(DC_I2C_DDC1_SPEED, DC_I2C_DDC1_THRESHOLD), 2); } +static bool acquire_engine(struct dce_i2c_hw *dce_i2c_hw) +{ + uint32_t arbitrate = 0; + + REG_GET(DC_I2C_ARBITRATION, DC_I2C_REG_RW_CNTL_STATUS, &arbitrate); + switch (arbitrate) { + case DC_I2C_STATUS__DC_I2C_STATUS_USED_BY_SW: + return true; + case DC_I2C_STATUS__DC_I2C_STATUS_USED_BY_HW: + return false; + case DC_I2C_STATUS__DC_I2C_STATUS_IDLE: + default: + break; + } + + REG_UPDATE(DC_I2C_ARBITRATION, DC_I2C_SW_USE_I2C_REG_REQ, true); + REG_GET(DC_I2C_ARBITRATION, DC_I2C_REG_RW_CNTL_STATUS, &arbitrate); + if (arbitrate != DC_I2C_STATUS__DC_I2C_STATUS_USED_BY_SW) + return false; + + return true; +} + static bool setup_engine( struct dce_i2c_hw *dce_i2c_hw) { + // Deassert soft reset to unblock I2C engine registers + REG_UPDATE(DC_I2C_CONTROL, DC_I2C_SOFT_RESET, false); + uint32_t i2c_setup_limit = I2C_SETUP_TIME_LIMIT_DCE; uint32_t reset_length = 0; @@ -309,8 +335,8 @@ static bool setup_engine( REG_UPDATE_N(SETUP, 1, FN(DC_I2C_DDC1_SETUP, DC_I2C_DDC1_CLK_EN), 1); - /* we have checked I2c not used by DMCU, set SW use I2C REQ to 1 to indicate SW using it*/ - REG_UPDATE(DC_I2C_ARBITRATION, DC_I2C_SW_USE_I2C_REG_REQ, 1); + if (!acquire_engine(dce_i2c_hw)) + return false; /*set SW requested I2c speed to default, if API calls in it will be override later*/ set_speed(dce_i2c_hw, dce_i2c_hw->ctx->dc->caps.i2c_speed_in_khz); @@ -319,9 +345,8 @@ static bool setup_engine( i2c_setup_limit = dce_i2c_hw->setup_limit; /* Program pin select */ - REG_UPDATE_6(DC_I2C_CONTROL, + REG_UPDATE_5(DC_I2C_CONTROL, DC_I2C_GO, 0, - DC_I2C_SOFT_RESET, 0, DC_I2C_SEND_RESET, 0, DC_I2C_SW_STATUS_RESET, 1, DC_I2C_TRANSACTION_COUNT, 0, @@ -351,6 +376,26 @@ static bool setup_engine( return true; } +/** + * If we boot without an HDMI display, the I2C engine does not get initialized + * correctly. One of its symptoms is that SW_USE_I2C does not get cleared after + * acquire, so that after setting SW_DONE_USING_I2C on release, the engine gets + * immediately reacquired by SW, preventing DMUB from using it. + */ +static void cntl_stuck_hw_workaround(struct dce_i2c_hw *dce_i2c_hw) +{ + uint32_t arbitrate = 0; + + REG_GET(DC_I2C_ARBITRATION, DC_I2C_REG_RW_CNTL_STATUS, &arbitrate); + if (arbitrate != DC_I2C_STATUS__DC_I2C_STATUS_USED_BY_SW) + return; + + // Still acquired after release, release again as a workaround + REG_UPDATE(DC_I2C_ARBITRATION, DC_I2C_SW_DONE_USING_I2C_REG, true); + REG_GET(DC_I2C_ARBITRATION, DC_I2C_REG_RW_CNTL_STATUS, &arbitrate); + ASSERT(arbitrate != DC_I2C_STATUS__DC_I2C_STATUS_USED_BY_SW); +} + static void release_engine( struct dce_i2c_hw *dce_i2c_hw) { @@ -378,9 +423,9 @@ static void release_engine( /*for HW HDCP Ri polling failure w/a test*/ set_speed(dce_i2c_hw, dce_i2c_hw->ctx->dc->caps.i2c_speed_in_khz_hdcp); - /* Release I2C after reset, so HW or DMCU could use it */ - REG_UPDATE_2(DC_I2C_ARBITRATION, DC_I2C_SW_DONE_USING_I2C_REG, 1, - DC_I2C_SW_USE_I2C_REG_REQ, 0); + // Release I2C engine so it can be used by HW or DMCU, automatically clears SW_USE_I2C + REG_UPDATE(DC_I2C_ARBITRATION, DC_I2C_SW_DONE_USING_I2C_REG, true); + cntl_stuck_hw_workaround(dce_i2c_hw); if (dce_i2c_hw->ctx->dc->debug.enable_mem_low_power.bits.i2c) { if (dce_i2c_hw->regs->DIO_MEM_PWR_CTRL) -- 2.47.2