On platforms with multiple display subsystems, such as SA8775P, the GPU
binds to the first display subsystem that probes. This implicit binding
prevents subsequent display subsystems from probing successfully,
breaking multi-display support.
Use the tristate separate_gpu_kms module parameter with the default
value set to auto (-1). In auto mode, the driver selects the binding
behavior based on the number of GPUs and display subsystems. This allows
display subsystems to probe independently when required, while
preserving the existing single-card behavior on simpler systems.
The separate_gpu_kms module parameter has the following semantics:
-1 (auto, default):
Select the binding mode based on hardware topology. If exactly one
GPU and one display subsystem are present, bind them together to
form a single DRM device. Otherwise, expose the GPU and display
subsystems as separate DRM devices.
0:
Always bind the GPU and display together to form a single DRM
device.
1:
Always expose the GPU and display subsystems as separate DRM
devices.
This ensures correct probing on multi-display platforms without
affecting single-display, single-GPU systems.
Signed-off-by: Mahadevan P <[email protected]>
---
Changes in v2:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v1:
https://lore.kernel.org/r/[email protected]
---
Depends on:
https://lore.kernel.org/lkml/[email protected]/
When separate_gpu_kms is enabled, the GPU and display drivers are
probed independently. In this configuration, the Adreno GPU driver
may no longer be loaded implicitly via the display subsystem.
The referenced patch adds a MODULE_DEVICE_TABLE() entry for the
Adreno GPU device, ensuring proper module autoloading based on
device tree matching. This is required to guarantee that the GPU
driver is loaded correctly when GPU and display probing are
decoupled.
Changes in v2:
- Drop dependency on Lemans dual-DPU device tree changes as this patch
works independently (Dmitry)
- Switch separate_gpu_kms to tristate and default to auto mode (Rob)
- Rename msm_gpu_no_components() to msm_separate_gpu_kms_components() for
clarity
- Link to v1:
https://lore.kernel.org/r/[email protected]
---
drivers/gpu/drm/msm/adreno/adreno_device.c | 2 +-
drivers/gpu/drm/msm/msm_drv.c | 52 ++++++++++++++++++++++++++----
drivers/gpu/drm/msm/msm_drv.h | 4 ++-
drivers/gpu/drm/msm/msm_mdss.c | 15 +++++++++
4 files changed, 64 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c
b/drivers/gpu/drm/msm/adreno/adreno_device.c
index 4edfe80c5be7..e40648c05797 100644
--- a/drivers/gpu/drm/msm/adreno/adreno_device.c
+++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
@@ -272,7 +272,7 @@ static const struct component_ops a3xx_ops = {
static int adreno_probe(struct platform_device *pdev)
{
if (of_device_is_compatible(pdev->dev.of_node, "amd,imageon") ||
- msm_gpu_no_components())
+ msm_separate_gpu_kms_components())
return msm_gpu_probe(pdev, &a3xx_ops);
return component_add(&pdev->dev, &a3xx_ops);
diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index e5ab1e28851d..575d1aea7927 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -54,16 +54,54 @@ static bool modeset = true;
MODULE_PARM_DESC(modeset, "Use kernel modesetting [KMS] (1=on (default),
0=disable)");
module_param(modeset, bool, 0600);
-static bool separate_gpu_kms;
-MODULE_PARM_DESC(separate_gpu_drm, "Use separate DRM device for the GPU
(0=single DRM device for both GPU and display (default), 1=two DRM devices)");
-module_param(separate_gpu_kms, bool, 0400);
+/*
+ * separate_gpu_kms (tristate):
+ * -1 (default): decide automatically based on hardware topology. Split
devices
+ * if there is more than one GPU or more than one display
master.
+ * 0: force single DRM device (bind display + GPU)
+ * 1: force separate DRM devices
+ */
+static int separate_gpu_kms = -1;
+MODULE_PARM_DESC(separate_gpu_kms,
+ "Use separate DRM device for the GPU (-1=auto (default),
0=single DRM device, 1=separate DRM devices)");
+module_param(separate_gpu_kms, int, 0400);
DECLARE_FAULT_ATTR(fail_gem_alloc);
DECLARE_FAULT_ATTR(fail_gem_iova);
-bool msm_gpu_no_components(void)
+static const struct of_device_id msm_gpu_match[];
+static int msm_count_gpus(void)
+{
+ struct device_node *np;
+ int count = 0;
+
+ for_each_matching_node(np, msm_gpu_match) {
+ if (of_device_is_available(np) && adreno_has_gpu(np))
+ count++;
+ }
+
+ return count;
+}
+
+static bool msm_separate_gpu_kms_auto(void)
+{
+ int gpus = msm_count_gpus();
+ int mdss = msm_mdss_count_masters();
+
+ if (gpus <= 0 || mdss <= 0)
+ return false;
+
+ /* If exactly one GPU and one display subsystem single card */
+ return (gpus > 1) || (mdss > 1);
+}
+
+bool msm_separate_gpu_kms_components(void)
{
- return separate_gpu_kms;
+ if (separate_gpu_kms == 1)
+ return true;
+ if (separate_gpu_kms == 0)
+ return false;
+ return msm_separate_gpu_kms_auto();
}
static int msm_drm_uninit(struct device *dev, const struct component_ops
*gpu_ops)
@@ -1030,7 +1068,7 @@ static int add_gpu_components(struct device *dev,
static int msm_drm_bind(struct device *dev)
{
return msm_drm_init(dev,
- msm_gpu_no_components() ?
+ msm_separate_gpu_kms_components() ?
&msm_kms_driver :
&msm_driver,
NULL);
@@ -1069,7 +1107,7 @@ int msm_drv_probe(struct device *master_dev,
return ret;
}
- if (!msm_gpu_no_components()) {
+ if (!msm_separate_gpu_kms_components()) {
ret = add_gpu_components(master_dev, &match);
if (ret)
return ret;
diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index 6d847d593f1a..64a5ad35f7a2 100644
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -555,6 +555,8 @@ void msm_kms_shutdown(struct platform_device *pdev);
bool msm_disp_drv_should_bind(struct device *dev, bool dpu_driver);
-bool msm_gpu_no_components(void);
+bool msm_separate_gpu_kms_components(void);
+
+int msm_mdss_count_masters(void);
#endif /* __MSM_DRV_H__ */
diff --git a/drivers/gpu/drm/msm/msm_mdss.c b/drivers/gpu/drm/msm/msm_mdss.c
index 9047e8d9ee89..00e3ac7dab3a 100644
--- a/drivers/gpu/drm/msm/msm_mdss.c
+++ b/drivers/gpu/drm/msm/msm_mdss.c
@@ -73,6 +73,21 @@ static int msm_mdss_parse_data_bus_icc_path(struct device
*dev,
return 0;
}
+static const struct of_device_id mdss_dt_match[];
+
+int msm_mdss_count_masters(void)
+{
+ struct device_node *np;
+ int count = 0;
+
+ for_each_matching_node(np, mdss_dt_match) {
+ if (of_device_is_available(np))
+ count++;
+ }
+
+ return count;
+}
+
static void msm_mdss_irq(struct irq_desc *desc)
{
struct msm_mdss *msm_mdss = irq_desc_get_handler_data(desc);
---
base-commit: b84a0ebe421ca56995ff78b66307667b62b3a900
change-id: 20260316-separate_gpu_kms-04d2cf4d91e2
Best regards,
--
Mahadevan P <[email protected]>
