[PATCH v2] drm/msm/dpu: Move min BW request and full BW disable back to mdss

Douglas Anderson dianders at chromium.org
Tue May 31 23:01:26 UTC 2022

In commit a670ff578f1f ("drm/msm/dpu: always use mdp device to scale
bandwidth") we fully moved interconnect stuff to the DPU driver. This
had no change for sc7180 but _did_ have an impact for other SoCs. It
made them match the sc7180 scheme.

Unfortunately, the sc7180 scheme seems like it was a bit broken.
Specifically the interconnect needs to be on for more than just the
DPU driver's AXI bus. In the very least it also needs to be on for the
DSI driver's AXI bus. This can be seen fairly easily by doing this on
a ChromeOS sc7180-trogdor class device:

  set_power_policy --ac_screen_dim_delay=5 --ac_screen_off_delay=10
  sleep 10
  cd /sys/bus/platform/devices/ae94000.dsi/power
  echo on > control

When you do that, you'll get a warning splat in the logs about
"gcc_disp_hf_axi_clk status stuck at 'off'".

One could argue that perhaps what I have done above is "illegal" and
that it can't happen naturally in the system because in normal system
usage the DPU is pretty much always on when DSI is on. That being
* In official ChromeOS builds (admittedly a 5.4 kernel with backports)
  we have seen that splat at bootup.
* Even though we don't use "autosuspend" for these components, we
  don't use the "put_sync" variants. Thus plausibly the DSI could stay
  "runtime enabled" past when the DPU is enabled. Techncially we
  shouldn't do that if the DPU's suspend ends up yanking our clock.

Let's change things such that the "bare minimum" request for the
interconnect happens in the mdss driver again. That means that all of
the children can assume that the interconnect is on at the minimum
bandwidth. We'll then let the DPU request the higher amount that it

It should be noted that this isn't as hacky of a solution as it might
initially appear. Specifically:
* Since MDSS and DPU individually get their own references to the
  interconnect then the framework will actually handle aggregating
  them. The two drivers are _not_ clobbering each other.
* When the Qualcomm interconnect driver aggregates it takes the max of
  all the peaks. Thus having MDSS request a peak, as we're doing here,
  won't actually change the total interconnect bandwidth (it won't be
  added to the request for the DPU). This perhaps explains why the
  "average" requested in MDSS was historically 0 since that one
  _would_ be added in.

NOTE also that in the downstream ChromeOS 5.4 and 5.15 kernels, we're
also seeing some RPMH hangs that are addressed by this fix. These
hangs are showing up in the field and on _some_ devices with enough
stress testing of suspend/resume. Specifically right at suspend time
with a stack crawl that looks like this (from chromeos-5.15 tree):

We don't completely understand all the mechanisms in play, but the
hang seemed to come and go with random factors. It's not terribly
surprising that the hang is gone after this patch since the line of
code that was failing is no longer present in the kernel.

Fixes: a670ff578f1f ("drm/msm/dpu: always use mdp device to scale bandwidth")
Fixes: c33b7c0389e1 ("drm/msm/dpu: add support for clk and bw scaling for display")
Signed-off-by: Douglas Anderson <dianders at chromium.org>

Changes in v2:
- Don't set bandwidth in init.

 drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c |  8 ----
 drivers/gpu/drm/msm/msm_mdss.c          | 57 +++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
index 2b9d931474e0..3025184053e0 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
@@ -49,8 +49,6 @@
 #define DPU_DEBUGFS_DIR "msm_dpu"
 #define DPU_DEBUGFS_HWMASKNAME "hw_log_mask"
-#define MIN_IB_BW	400000000ULL /* Min ib vote 400MB */
 static int dpu_kms_hw_init(struct msm_kms *kms);
 static void _dpu_kms_mmu_destroy(struct dpu_kms *dpu_kms);
@@ -1303,15 +1301,9 @@ static int __maybe_unused dpu_runtime_resume(struct device *dev)
 	struct dpu_kms *dpu_kms = to_dpu_kms(priv->kms);
 	struct drm_encoder *encoder;
 	struct drm_device *ddev;
-	int i;
 	ddev = dpu_kms->dev;
-	WARN_ON(!(dpu_kms->num_paths));
-	/* Min vote of BW is required before turning on AXI clk */
-	for (i = 0; i < dpu_kms->num_paths; i++)
-		icc_set_bw(dpu_kms->path[i], 0, Bps_to_icc(MIN_IB_BW));
 	rc = clk_bulk_prepare_enable(dpu_kms->num_clocks, dpu_kms->clocks);
 	if (rc) {
 		DPU_ERROR("clock enable failed rc:%d\n", rc);
diff --git a/drivers/gpu/drm/msm/msm_mdss.c b/drivers/gpu/drm/msm/msm_mdss.c
index 0454a571adf7..e13c5c12b775 100644
--- a/drivers/gpu/drm/msm/msm_mdss.c
+++ b/drivers/gpu/drm/msm/msm_mdss.c
@@ -5,6 +5,7 @@
 #include <linux/clk.h>
 #include <linux/delay.h>
+#include <linux/interconnect.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
 #include <linux/irqdesc.h>
@@ -25,6 +26,8 @@
 #define UBWC_CTRL_2			0x150
 #define UBWC_PREDICTION_MODE		0x154
+#define MIN_IB_BW	400000000UL /* Min ib vote 400MB */
 struct msm_mdss {
 	struct device *dev;
@@ -36,8 +39,47 @@ struct msm_mdss {
 		unsigned long enabled_mask;
 		struct irq_domain *domain;
 	} irq_controller;
+	struct icc_path *path[2];
+	u32 num_paths;
+static int msm_mdss_parse_data_bus_icc_path(struct device *dev,
+					    struct msm_mdss *msm_mdss)
+	struct icc_path *path0 = of_icc_get(dev, "mdp0-mem");
+	struct icc_path *path1 = of_icc_get(dev, "mdp1-mem");
+	if (IS_ERR_OR_NULL(path0))
+		return PTR_ERR_OR_ZERO(path0);
+	msm_mdss->path[0] = path0;
+	msm_mdss->num_paths = 1;
+	if (!IS_ERR_OR_NULL(path1)) {
+		msm_mdss->path[1] = path1;
+		msm_mdss->num_paths++;
+	}
+	return 0;
+static void msm_mdss_put_icc_path(void *data)
+	struct msm_mdss *msm_mdss = data;
+	int i;
+	for (i = 0; i < msm_mdss->num_paths; i++)
+		icc_put(msm_mdss->path[i]);
+static void msm_mdss_icc_request_bw(struct msm_mdss *msm_mdss, unsigned long bw)
+	int i;
+	for (i = 0; i < msm_mdss->num_paths; i++)
+		icc_set_bw(msm_mdss->path[i], 0, Bps_to_icc(bw));
 static void msm_mdss_irq(struct irq_desc *desc)
 	struct msm_mdss *msm_mdss = irq_desc_get_handler_data(desc);
@@ -136,6 +178,13 @@ static int msm_mdss_enable(struct msm_mdss *msm_mdss)
 	int ret;
+	/*
+	 * Several components have AXI clocks that can only be turned on if
+	 * the interconnect is enabled (non-zero bandwidth). Let's make sure
+	 * that the interconnects are at least at a minimum amount.
+	 */
+	msm_mdss_icc_request_bw(msm_mdss, MIN_IB_BW);
 	ret = clk_bulk_prepare_enable(msm_mdss->num_clocks, msm_mdss->clocks);
 	if (ret) {
 		dev_err(msm_mdss->dev, "clock enable failed, ret:%d\n", ret);
@@ -178,6 +227,7 @@ static int msm_mdss_enable(struct msm_mdss *msm_mdss)
 static int msm_mdss_disable(struct msm_mdss *msm_mdss)
 	clk_bulk_disable_unprepare(msm_mdss->num_clocks, msm_mdss->clocks);
+	msm_mdss_icc_request_bw(msm_mdss, 0);
 	return 0;
@@ -271,6 +321,13 @@ static struct msm_mdss *msm_mdss_init(struct platform_device *pdev, bool is_mdp5
 	dev_dbg(&pdev->dev, "mapped mdss address space @%pK\n", msm_mdss->mmio);
+	ret = msm_mdss_parse_data_bus_icc_path(&pdev->dev, msm_mdss);
+	if (ret)
+		return ERR_PTR(ret);
+	ret = devm_add_action_or_reset(&pdev->dev, msm_mdss_put_icc_path, msm_mdss);
+	if (ret)
+		return ERR_PTR(ret);
 	if (is_mdp5)
 		ret = mdp5_mdss_parse_clock(pdev, &msm_mdss->clocks);

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