linux-kernel - [PATCH v4 10/10] drm/msm/a6xx: Poll for GBIF unhalt status in hw

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Message-Id: <20230628-topic-a7xx_drmmsm-v4-10-8b3e402795c1@linaro.org>
Date:   Tue, 12 Sep 2023 12:04:52 +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>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Neil Armstrong <neil.armstrong@...aro.org>
Subject: [PATCH v4 10/10] drm/msm/a6xx: Poll for GBIF unhalt status in
 hw_init

Some GPUs - particularly A7xx ones - are really really stubborn and
sometimes take a longer-than-expected time to finish unhalting GBIF.

Note that this is not caused by the request a few lines above.

Poll for the unhalt ack to make sure we're not trying to write bits to
an essentially dead GPU that can't receive data on its end of the bus.
Failing to do this will result in inexplicable GMU timeouts or worse.

This is a rather ugly hack which introduces a whole lot of latency.

Tested-by: Neil Armstrong <neil.armstrong@...aro.org> # on SM8550-QRD
Tested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org> # sm8450
Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
---
 drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
index 2313620084b6..11cb410e0ac7 100644
--- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
@@ -1629,6 +1629,10 @@ static int hw_init(struct msm_gpu *gpu)
 		mb();
 	}
 
+	/* Some GPUs are stubborn and take their sweet time to unhalt GBIF! */
+	if (adreno_is_a7xx(adreno_gpu) && a6xx_has_gbif(adreno_gpu))
+		spin_until(!gpu_read(gpu, REG_A6XX_GBIF_HALT_ACK));
+
 	gpu_write(gpu, REG_A6XX_RBBM_SECVID_TSB_CNTL, 0);
 
 	if (adreno_is_a619_holi(adreno_gpu))

-- 
2.42.0