linux-kernel - [PATCH v4 4/6] drm/msm/a6xx: Ensure clean GMU state in a6xx_gmu_fw

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Message-Id: <20230517-topic-a7xx_prep-v4-4-b16f273a91d4@linaro.org>
Date:   Tue, 20 Jun 2023 13:10:39 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Konrad Dybcio <konrad.dybcio@...aro.org>
Subject: [PATCH v4 4/6] drm/msm/a6xx: Ensure clean GMU state in
 a6xx_gmu_fw_start

While it's not very well understood, there is some sort of a fault
handler implemented in the GMU firmware which triggers when a certain
bit is set, resulting in the M3 core not booting up the way we expect
it to.

Write a magic value to a magic register to hopefully prevent that
from happening.

Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
---
 drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
index 5deb79924897..9929ff187368 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
@@ -790,6 +790,12 @@ static int a6xx_gmu_fw_start(struct a6xx_gmu *gmu, unsigned int state)
 	gmu_write(gmu, REG_A6XX_GMU_AHB_FENCE_RANGE_0,
 		(1 << 31) | (0xa << 18) | (0xa0));
 
+	/*
+	 * Snapshots toggle the NMI bit which will result in a jump to the NMI
+	 * handler instead of __main. Set the M3 config value to avoid that.
+	 */
+	gmu_write(gmu, REG_A6XX_GMU_CM3_CFG, 0x4052);
+
 	chipid = adreno_gpu->rev.core << 24;
 	chipid |= adreno_gpu->rev.major << 16;
 	chipid |= adreno_gpu->rev.minor << 12;

-- 
2.41.0