On Mon, Oct 26, 2026 at 11:51:30AM +0530, Jayant Shekhar wrote:
> Add the DCP function driver that binds the VirtIO device to MSM
> DRM. Without a function driver, Linux cannot establish HFI queues,
> discover firmware capabilities, or register the firmware-owned
> display backend.
>
> Set up the DCP DMA and IOMMU identity, initialize VirtIO and HFI
> transport, register the MSM DRM component, and synchronize suspend,
> resume, remove, and shutdown with in-flight HFI activity.
>
> Assisted-by: LLM
> Signed-off-by: Jayant Shekhar <[email protected]>
> ---
> drivers/gpu/drm/msm/Makefile | 2 +
> drivers/gpu/drm/msm/dcp/dcp_drv.c | 191 ++++++++++++++++++++++++++
> drivers/gpu/drm/msm/dcp/dcp_drv.h | 17 +++
> drivers/gpu/drm/msm/dcp/dcp_virtio.c | 258
> +++++++++++++++++++++++++++++++++++
> drivers/gpu/drm/msm/dcp/dcp_virtio.h | 2 +
> drivers/gpu/drm/msm/msm_drv.c | 6 +-
> drivers/gpu/drm/msm/msm_drv.h | 2 +
> 7 files changed, 475 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/Makefile b/drivers/gpu/drm/msm/Makefile
> index e1a995a8c980..ffdb159dd9ad 100644
> --- a/drivers/gpu/drm/msm/Makefile
> +++ b/drivers/gpu/drm/msm/Makefile
> @@ -85,6 +85,8 @@ msm-display-$(CONFIG_DRM_MSM_DCP) += \
> dcp/dcp_hfi_plane.o \
> dcp/dcp_ipcc.o \
> dcp/dcp_encoder.o \
> + dcp/dcp_drv.o \
> + dcp/dcp_virtio.o \
> dcp/dcp_virtio_transport.o \
> dcp/hfi/hfi_packer.o \
> dcp/hfi/hfi_unpacker.o \
> diff --git a/drivers/gpu/drm/msm/dcp/dcp_drv.c
> b/drivers/gpu/drm/msm/dcp/dcp_drv.c
> new file mode 100644
> index 000000000000..8c38de883bf6
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/dcp/dcp_drv.c
> @@ -0,0 +1,191 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + * DCP VirtIO driver.
> + */
> +
> +#include <linux/component.h>
> +#include <linux/device.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/panic_notifier.h>
> +#include <linux/pm_runtime.h>
> +
> +#define DCP_DPU_AUTOSUSPEND_DELAY_MS 5000
> +
> +#include "dcp_drv.h"
> +#include "dcp_dpu_kms.h"
> +#include "dcp_hfi.h"
> +#include "dcp_ipcc.h"
> +#include "dcp_virtio.h"
> +#include "msm_drv.h"
> +#include "msm_kms.h"
> +
> +int dcp_subsystem_dev_init(struct dcp_drv *drv)
> +{
> + struct virtio_device *vdev = drv->vdev;
> + struct device_node *dcp_subsystem_node;
> + struct platform_device *pdev;
> + struct device *dev;
> + char busid[32];
> + bool iommu_mapped;
> + int ret;
> +
> + dcp_subsystem_node = of_node_get(vdev->dev.of_node);
> + if (!dcp_subsystem_node) {
> + dev_err(&vdev->dev, "no DCP subsystem DT node\n");
> + return -ENODEV;
> + }
> +
> + snprintf(busid, sizeof(busid), "dcp-subsystem.%s",
> dev_name(vdev->dev.parent));
> +
> + /*
> + * DCP is discovered through VirtIO, but display/HFI buffers must be
> + * mapped through the dcp-subsystem node's DMA/IOMMU identity. Create a
> + * platform device for that DT node so DMA API and msm_kms_init_vm() use
Does DMA API require platform_device or would it work with the generic
struct device? In the latter case, should the MSM layer be changed to
pass struct device instead of struct platform_device?
> + * the display function's IOMMU domain.
> + */
> + pdev = of_platform_device_create(dcp_subsystem_node, busid,
> vdev->dev.parent);
> + if (!pdev) {
> + dev_err(&vdev->dev, "dcp_subsystem_dev creation failed\n");
> + of_node_put(dcp_subsystem_node);
> + return -ENODEV;
> + }
> + dev = &pdev->dev;
> +
> + dev->dma_parms = &drv->dcp_subsystem_dma_parms;
> + dma_set_max_seg_size(dev, UINT_MAX);
> +
> + ret = of_dma_configure_id(dev, dcp_subsystem_node, true, NULL);
> + if (ret) {
> + dev_err(dev, "of_dma_configure_id failed: %d\n", ret);
> + goto err_destroy;
> + }
> +
> + iommu_mapped = device_iommu_mapped(dev);
> + if (!iommu_mapped) {
> + dev_err(dev, "no IOMMU group attached\n");
> + ret = -ENODEV;
> + goto err_destroy;
> + }
> +
> + dev_dbg(dev, "dcp-subsystem: iommu_mapped=%d iommu_group=%d\n",
> + iommu_mapped,
> + dev->iommu_group ? iommu_group_id(dev->iommu_group) : -1);
> +
> + pm_runtime_set_active(dev);
> + pm_runtime_enable(dev);
> + pm_runtime_set_autosuspend_delay(dev, DCP_DPU_AUTOSUSPEND_DELAY_MS);
> + pm_runtime_use_autosuspend(dev);
> +
> + drv->dcp_subsystem_dev = pdev;
> + drv->dcp_subsystem_node = dcp_subsystem_node;
> +
> + return 0;
> +
> +err_destroy:
> + of_platform_device_destroy(dev, NULL);
> + of_node_put(dcp_subsystem_node);
> + return ret;
> +}
> +
> +void dcp_subsystem_dev_deinit(struct dcp_drv *drv)
> +{
> + if (!drv->dcp_subsystem_dev)
> + return;
> +
> + pm_runtime_disable(&drv->dcp_subsystem_dev->dev);
> + of_platform_device_destroy(&drv->dcp_subsystem_dev->dev, NULL);
> + of_node_put(drv->dcp_subsystem_node);
> + drv->dcp_subsystem_dev = NULL;
> +}
> +
> +int dcp_pm_prepare(struct device *vdev_dev)
> +{
> + struct dcp_drv *drv = vdev_dev ?
> + dev_to_virtio(vdev_dev)->priv : NULL;
> +
> + if (!drv || !drv->dcp_subsystem_dev)
> + return 0;
> +
> + return msm_kms_pm_prepare(&drv->dcp_subsystem_dev->dev);
> +}
> +
> +void dcp_pm_complete(struct device *vdev_dev)
> +{
> + struct dcp_drv *drv = vdev_dev ?
> + dev_to_virtio(vdev_dev)->priv : NULL;
> +
> + if (!drv || !drv->dcp_subsystem_dev)
> + return;
> +
> + msm_kms_pm_complete(&drv->dcp_subsystem_dev->dev);
> +}
> +
> +int dcp_component_register(struct dcp_drv *drv)
> +{
> + struct device *dev = &drv->dcp_subsystem_dev->dev;
> + struct component_match *match = NULL;
> + int ret;
> +
> + ret = dcp_dpu_kms_init_dsi_bridges(drv->kms, &match);
> + if (ret) {
> + dev_err(dev, "DSI host initialization failed: %d\n", ret);
> + dcp_dpu_kms_cleanup_bridges(drv->kms);
> + return ret;
> + }
> +
> + /* A GPU is optional for the DCP display-only DRM device. */
> + msm_add_gpu_components(dev, &match);
Missign error handling.
> +
> + ret = component_master_add_with_match(dev, &msm_drm_ops, match);
> + if (ret) {
> + dev_err(dev, "component_master_add_with_match failed: %d\n",
> + ret);
> + dcp_dpu_kms_cleanup_bridges(drv->kms);
> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +void dcp_component_unregister(struct dcp_drv *drv)
> +{
> + struct device *dev = &drv->dcp_subsystem_dev->dev;
> +
> + component_master_del(dev, &msm_drm_ops);
> + dcp_dpu_kms_cleanup_bridges(drv->kms);
> +}
> +
> +static int dcp_panic_notifier_cb(struct notifier_block *nb,
> + unsigned long action, void *data)
> +{
> + struct dcp_drv *drv = container_of(nb, struct dcp_drv, panic_notifier);
> +
> + if (drv->hfi)
> + atomic_set(&drv->hfi->shutdown_in_progress, 1);
> +
> + return NOTIFY_OK;
> +}
> +
> +void dcp_panic_notifier_register(struct dcp_drv *drv)
> +{
> + drv->panic_notifier.notifier_call = dcp_panic_notifier_cb;
> + atomic_notifier_chain_register(&panic_notifier_list,
> &drv->panic_notifier);
> +}
> +
> +void dcp_panic_notifier_unregister(struct dcp_drv *drv)
> +{
> + atomic_notifier_chain_unregister(&panic_notifier_list,
> &drv->panic_notifier);
> +}
> +
> +void __init msm_dcp_register(void)
> +{
> + dcp_virtio_register();
> +}
> +
> +void __exit msm_dcp_unregister(void)
> +{
> + dcp_virtio_unregister();
> +}
> diff --git a/drivers/gpu/drm/msm/dcp/dcp_drv.h
> b/drivers/gpu/drm/msm/dcp/dcp_drv.h
> index 16f87035cb9a..3adc5855a9a2 100644
> --- a/drivers/gpu/drm/msm/dcp/dcp_drv.h
> +++ b/drivers/gpu/drm/msm/dcp/dcp_drv.h
> @@ -14,6 +14,7 @@
> #include "dcp_ipcc.h"
>
> struct dcp_dpu_kms;
> +struct component_match;
>
> struct dcp_drv {
> struct virtio_device *vdev;
> @@ -24,6 +25,22 @@ struct dcp_drv {
> struct dcp_dpu_kms *kms;
> struct dcp_caps caps;
> struct notifier_block panic_notifier;
> + struct dcp_ipcc *ipcc;
> };
>
> +int dcp_subsystem_dev_init(struct dcp_drv *drv);
> +void dcp_subsystem_dev_deinit(struct dcp_drv *drv);
> +
> +int dcp_component_register(struct dcp_drv *drv);
> +void dcp_component_unregister(struct dcp_drv *drv);
> +
> +int dcp_pm_prepare(struct device *vdev_dev);
> +void dcp_pm_complete(struct device *vdev_dev);
> +
> +void dcp_panic_notifier_register(struct dcp_drv *drv);
> +void dcp_panic_notifier_unregister(struct dcp_drv *drv);
> +
> +void __init msm_dcp_register(void);
> +void __exit msm_dcp_unregister(void);
> +
> #endif /* __DCP_DRV_H__ */
> diff --git a/drivers/gpu/drm/msm/dcp/dcp_virtio.c
> b/drivers/gpu/drm/msm/dcp/dcp_virtio.c
> new file mode 100644
> index 000000000000..15d5caf02ff5
> --- /dev/null
> +++ b/drivers/gpu/drm/msm/dcp/dcp_virtio.c
> @@ -0,0 +1,258 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + * DCP VirtIO device driver.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/err.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <linux/slab.h>
> +
> +#include "dcp_drv.h"
> +#include "dcp_dpu_kms.h"
> +#include "dcp_hfi.h"
> +#include "dcp_ipcc.h"
> +#include "dcp_virtio.h"
> +#include "msm_drv.h"
> +#include "msm_kms.h"
> +
> +static void dcp_virtio_hfi_cleanup(struct dcp_drv *drv);
> +
> +static const unsigned int dcp_virtio_features[] = {
> + VIRTIO_F_VERSION_1,
> + VIRTIO_F_NOTIFICATION_DATA,
> + VIRTIO_F_RING_RESET,
> + VIRTIO_F_ACCESS_PLATFORM,
> +};
> +
> +/*
> + * The VirtIO core owns transport discovery. This driver owns HFI setup and
> + * creates the DRM component only after firmware capabilities are available.
> + */
> +static int dcp_virtio_probe(struct virtio_device *vdev)
> +{
> + struct dcp_drv *drv;
> + struct virtqueue *vqs[DCP_NUM_VQS];
> + struct virtqueue_info vqs_info[DCP_NUM_VQS] = {
> + [DCP_VQ_CMD] = { .name = "cmd", .callback =
> dcp_hfi_cmd_callback },
> + [DCP_VQ_RESP] = { .name = "resp", .callback =
> dcp_hfi_resp_callback },
> + };
> + struct dcp_dpu_kms *dcp_kms;
> + struct msm_drm_private *priv;
> + int ret;
> +
> + dev_dbg(&vdev->dev, "DCP VirtIO probe started\n");
> +
> + drv = devm_kzalloc(&vdev->dev, sizeof(*drv), GFP_KERNEL);
> + if (!drv)
> + return -ENOMEM;
> +
> + drv->vdev = vdev;
> + vdev->priv = drv;
> +
> + if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> + dev_err(&vdev->dev, "VIRTIO_F_VERSION_1 not negotiated\n");
> + return -ENODEV;
> + }
> +
> + drv->ipcc = dcp_virtio_get_ipcc(vdev);
Here you are breaking the abstraction boundary. The DCP is a VirtIO
device. You should not use IPCC to communicate with it.
> + /* Access-platform is required for the firmware-visible IOVA mappings.
> */
> + if (!virtio_has_feature(vdev, VIRTIO_F_ACCESS_PLATFORM)) {
> + dev_err(&vdev->dev, "VIRTIO_F_ACCESS_PLATFORM not
> negotiated\n");
> + return -ENODEV;
> + }
> +
> + ret = dcp_subsystem_dev_init(drv);
> + if (ret)
> + return ret;
> +
> + ret = virtio_find_vqs(vdev, DCP_NUM_VQS, vqs, vqs_info, NULL);
> + if (ret) {
> + dev_err(&vdev->dev, "virtqueue allocation failed: %d\n", ret);
> + goto err_fn_dev;
> + }
> +
> + ret = dcp_hfi_init(drv, vdev, vqs[DCP_VQ_CMD], vqs[DCP_VQ_RESP],
> + vdev->dev.parent);
> + if (ret) {
> + dev_err(&vdev->dev, "HFI init failed: %d\n", ret);
> + goto err_del_vqs;
> + }
> +
> + dcp_ipcc_set_resp_vq(drv->ipcc, vqs[DCP_VQ_RESP]);
> +
> + /*
> + * Keep the device unready until HFI state and virtqueues are
> initialized.
> + * KMS registration below depends on synchronous firmware
> initialization.
> + */
> + virtio_device_ready(vdev);
> + virtqueue_kick(drv->hfi->resp_vq);
> +
> + ret = dcp_hfi_send_device_init(drv->hfi);
> + if (ret) {
> + dev_err(&vdev->dev, "HFI DEVICE_INIT failed: %d\n", ret);
> + goto err_hfi_deinit;
> + }
> +
> + ret = dcp_hfi_get_capabilities(drv->hfi, &drv->caps);
> + if (ret) {
> + dev_err(&vdev->dev, "HFI GET_CAPS failed: %d\n", ret);
> + goto err_hfi_deinit;
> + }
> +
> + /* Register the display resources before exposing the DRM component. */
> + ret = dcp_hfi_send_resource_register(drv->hfi);
> + if (ret) {
> + dev_err(&vdev->dev, "HFI RESOURCE_REGISTER failed: %d\n", ret);
> + goto err_hfi_deinit;
> + }
> +
> + dev_dbg(&vdev->dev,
> + "DCP caps: %u displays, max %ux%u, %u planes\n",
> + drv->caps.num_displays, drv->caps.max_width,
> drv->caps.max_height,
> + drv->caps.max_planes);
> +
> + dcp_kms = devm_kzalloc(&drv->dcp_subsystem_dev->dev, sizeof(*dcp_kms),
> GFP_KERNEL);
> + if (!dcp_kms) {
> + ret = -ENOMEM;
> + goto err_hfi_deinit;
> + }
> +
> + dcp_kms->drv = drv;
> + dcp_kms->pm_dev = &drv->dcp_subsystem_dev->dev;
> + dcp_kms->hfi = drv->hfi;
> + dcp_kms->caps = &drv->caps;
> + dcp_kms->dpus_np = drv->dcp_subsystem_node;
> + dcp_kms->iommu_dev = &drv->dcp_subsystem_dev->dev;
> + drv->kms = dcp_kms;
> +
> + ret = msm_kms_init(&dcp_kms->base, &dcp_dpu_kms_funcs);
> + if (ret) {
> + dev_err(&vdev->dev, "msm_kms_init failed: %d\n", ret);
> + goto err_hfi_deinit;
> + }
> +
> + priv = devm_kzalloc(&drv->dcp_subsystem_dev->dev, sizeof(*priv),
> GFP_KERNEL);
> + if (!priv) {
> + ret = -ENOMEM;
> + goto err_hfi_deinit;
> + }
> +
> + priv->kms = &dcp_kms->base;
> + priv->kms_init = dcp_kms_init;
> + dev_set_drvdata(&drv->dcp_subsystem_dev->dev, priv);
> + dcp_kms->rpm_enabled = true;
> +
> + /* Component binding now sees initialized HFI, capabilities, and IOMMU
> state. */
> + ret = dcp_component_register(drv);
> + if (ret) {
> + dev_err_probe(&vdev->dev, ret, "component register failed\n");
> + goto err_hfi_deinit;
> + }
> +
> + dcp_panic_notifier_register(drv);
> +
> + dev_dbg(&vdev->dev, "DCP VirtIO probe complete\n");
> + return 0;
> +
> +err_hfi_deinit:
> + dcp_virtio_hfi_cleanup(drv);
> + goto err_fn_dev;
> +err_del_vqs:
> + virtio_reset_device(vdev);
> + vdev->config->del_vqs(vdev);
> +err_fn_dev:
> + dcp_subsystem_dev_deinit(drv);
> + return ret;
> +}
> +
> +static void dcp_virtio_hfi_cleanup(struct dcp_drv *drv)
> +{
> + struct virtio_device *vdev = drv->vdev;
> +
> + if (!drv->hfi)
> + return;
> +
> + dcp_ipcc_set_resp_vq(drv->ipcc, NULL);
> +
> + dcp_hfi_stop(drv->hfi);
> + virtio_reset_device(vdev);
> + virtio_synchronize_cbs(vdev);
> + dcp_hfi_quiesce_queues(drv->hfi);
> + vdev->config->del_vqs(vdev);
> + dcp_hfi_deinit(drv->hfi);
> +}
> +
> +/* Remove DRM users before tearing down HFI, IPCC, or the VirtIO queues. */
> +static void dcp_virtio_remove(struct virtio_device *vdev)
> +{
> + struct dcp_drv *drv = vdev->priv;
> +
> + dev_dbg(&vdev->dev, "DCP VirtIO remove\n");
> +
> + dcp_component_unregister(drv);
> + dcp_panic_notifier_unregister(drv);
> +
> + dcp_virtio_hfi_cleanup(drv);
> +
> + dcp_subsystem_dev_deinit(drv);
> +}
> +
> +/* KMS shutdown must complete while the firmware transport is available. */
> +static void dcp_virtio_shutdown(struct virtio_device *vdev)
> +{
> + struct dcp_drv *drv = vdev->priv;
> +
> + pm_runtime_get_sync(&drv->dcp_subsystem_dev->dev);
> + msm_kms_shutdown(drv->dcp_subsystem_dev);
> + pm_runtime_put_noidle(&drv->dcp_subsystem_dev->dev);
> +}
> +
> +static const struct virtio_device_id dcp_virtio_id_table[] = {
> + { VIRTIO_ID_QPSFI, VIRTIO_VENDOR_ID_DCP_HFI },
What exactly does it mean? Are you using Vendor ID (which should be
Qualcomm) to distinguish between possible QPSFI devices?
> + { 0 },
> +};
> +MODULE_DEVICE_TABLE(virtio, dcp_virtio_id_table);
> +
> +static const struct dev_pm_ops dcp_virtio_pm_ops = {
> + .prepare = dcp_pm_prepare,
> + .complete = dcp_pm_complete,
> +};
> +
> +static struct virtio_driver dcp_virtio_driver = {
> + .driver = {
> + .name = "qcom-dcp-hfi",
> + .owner = THIS_MODULE,
> + .pm = &dcp_virtio_pm_ops,
> + },
> + .id_table = dcp_virtio_id_table,
> + .feature_table = dcp_virtio_features,
> + .feature_table_size = ARRAY_SIZE(dcp_virtio_features),
> + .probe = dcp_virtio_probe,
> + .remove = dcp_virtio_remove,
> + .shutdown = dcp_virtio_shutdown,
> +};
> +
> +int dcp_virtio_register(void)
> +{
> + int ret;
> +
> + ret = dcp_virtio_transport_register();
> + if (ret)
> + return ret;
> +
> + ret = register_virtio_driver(&dcp_virtio_driver);
> + if (ret)
> + dcp_virtio_transport_unregister();
> +
> + return ret;
> +}
> +
> +void dcp_virtio_unregister(void)
> +{
> + unregister_virtio_driver(&dcp_virtio_driver);
> + dcp_virtio_transport_unregister();
> +}
> diff --git a/drivers/gpu/drm/msm/dcp/dcp_virtio.h
> b/drivers/gpu/drm/msm/dcp/dcp_virtio.h
> index a9c3b9aff61d..3ded8293ab18 100644
> --- a/drivers/gpu/drm/msm/dcp/dcp_virtio.h
> +++ b/drivers/gpu/drm/msm/dcp/dcp_virtio.h
> @@ -8,9 +8,11 @@
>
> #include <linux/device.h>
> #include <linux/virtio.h>
> +#include <linux/virtio_ids.h>
>
> struct dcp_drv;
> struct dcp_ipcc;
> +#define VIRTIO_VENDOR_ID_DCP_HFI 1
Squatting the ID?
>
> struct dcp_ipcc *dcp_virtio_get_ipcc(struct virtio_device *vdev);
>
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 5e8f3ce26b32..5816c64d7ce7 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -1093,8 +1093,8 @@ static const struct of_device_id msm_gpu_match[] = {
> { },
> };
>
> -static int add_gpu_components(struct device *dev,
> - struct component_match **matchptr)
> +int msm_add_gpu_components(struct device *dev,
> + struct component_match **matchptr)
Separate commit.
> {
> struct device_node *np;
>
> @@ -1153,7 +1153,7 @@ int msm_drv_probe(struct device *master_dev,
> }
>
> if (!msm_separate_gpu_kms_components()) {
> - ret = add_gpu_components(master_dev, &match);
> + ret = msm_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 2840e8a5052d..aa5dfd82ac6f 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -523,6 +523,8 @@ static inline unsigned long timeout_to_jiffies(const
> ktime_t *timeout)
> /* Driver helpers */
>
> extern const struct component_master_ops msm_drm_ops;
> +int msm_add_gpu_components(struct device *dev,
> + struct component_match **matchptr);
>
> int msm_kms_pm_prepare(struct device *dev);
> void msm_kms_pm_complete(struct device *dev);
>
> --
> 2.43.0
>
--
With best wishes
Dmitry
