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Message-ID: <CAF6AEGtsnfxHYZyEsC+BSW0aWd1V4ZvM0c_wyTx20Vaeku4o6A@mail.gmail.com>
Date: Wed, 7 May 2025 09:43:10 -0700
From: Rob Clark <robdclark@...il.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Abhinav Kumar <quic_abhinavk@...cinc.com>, Dmitry Baryshkov <lumag@...nel.org>,
Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Konrad Dybcio <konradybcio@...nel.org>, linux-arm-msm@...r.kernel.org,
dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 10/11] drm/msm: enable separate binding of GPU and
display devices
On Sat, May 3, 2025 at 12:17 AM Dmitry Baryshkov
<dmitry.baryshkov@....qualcomm.com> wrote:
>
> There are cases when we want to have separate DRM devices for GPU and
> display pipelines.
> One example is development, when it is beneficial to be able to bind the
> GPU driver separately, without the display pipeline (and without the
> hacks adding "amd,imageon" to the compatible string).
> Another example is some of Qualcomm platforms, which have two MDSS
> units, but only one GPU. With current approach it is next to impossible
> to support this usecase properly, while separate binding allows users to
> have three DRM devices: two for MDSS units and a single headless GPU.
>
> Add kernel param msm.separate_gpu_drm, which if set to true forces
> creation of separate display and GPU DRM devices. Mesa supports this
> setup by using the kmsro wrapper.
>
> The param is disabled by default, in order to be able to test userspace
> for the compatibility issues. Simple clients are able to handle this
> setup automatically.
>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> ---
> drivers/gpu/drm/msm/adreno/adreno_device.c | 3 +-
> drivers/gpu/drm/msm/msm_drv.c | 49 +++++++++++++++++++++++++++---
> drivers/gpu/drm/msm/msm_drv.h | 2 ++
> 3 files changed, 49 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> index 325cb710ea08ac8e5c3d9c80c8d8e18e1946e994..2322a3301a5226c4e2590344e4744934addeea33 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> @@ -243,7 +243,8 @@ 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"))
> + if (of_device_is_compatible(pdev->dev.of_node, "amd,imageon") ||
> + msm_gpu_no_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 804b594ba1e7df9d9aec53a9be1451f1167fc77a..eec7501eb05b6c31ffd9dc5a7ba430e3284ea5ed 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -59,9 +59,18 @@ 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_drm;
> +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_drm, bool, 0400);
> +
> DECLARE_FAULT_ATTR(fail_gem_alloc);
> DECLARE_FAULT_ATTR(fail_gem_iova);
>
> +bool msm_gpu_no_components(void)
> +{
> + return separate_gpu_drm;
> +}
> +
> static int msm_drm_uninit(struct device *dev, const struct component_ops *gpu_ops)
> {
> struct platform_device *pdev = to_platform_device(dev);
> @@ -898,6 +907,32 @@ static const struct drm_driver msm_driver = {
> .patchlevel = MSM_VERSION_PATCHLEVEL,
> };
>
> +static const struct drm_driver msm_kms_driver = {
> + .driver_features = DRIVER_GEM |
> + DRIVER_ATOMIC |
> + DRIVER_MODESET |
> + DRIVER_SYNCOBJ_TIMELINE |
> + DRIVER_SYNCOBJ,
I think, drop DRIVER_SYNCOBJ + DRIVER_SYNCOBJ_TIMELINE, since kms only
uses fence fd's. (Syncobj support is only in the SUBMIT and upcoming
VM_BIND ioctls.. I don't think there is a use-case for being able to
create syncobjs for KMS only drivers, and it doesn't look like any of
the other kms-only drivers support this.)
Alternatively, we could use drm_device::driver_features to mask
certain drm_driver::driver_features at runtime.. that would be a way
to avoid having separate drm_driver tables.
BR,
-R
> + .open = msm_open,
> + .postclose = msm_postclose,
> + .dumb_create = msm_gem_dumb_create,
> + .dumb_map_offset = msm_gem_dumb_map_offset,
> + .gem_prime_import_sg_table = msm_gem_prime_import_sg_table,
> +#ifdef CONFIG_DEBUG_FS
> + .debugfs_init = msm_debugfs_init,
> +#endif
> + MSM_FBDEV_DRIVER_OPS,
> + .show_fdinfo = msm_show_fdinfo,
> + .ioctls = msm_ioctls,
> + .num_ioctls = ARRAY_SIZE(msm_ioctls),
> + .fops = &fops,
> + .name = "msm-kms",
> + .desc = "MSM Snapdragon DRM",
> + .major = MSM_VERSION_MAJOR,
> + .minor = MSM_VERSION_MINOR,
> + .patchlevel = MSM_VERSION_PATCHLEVEL,
> +};
> +
> static const struct drm_driver msm_gpu_driver = {
> .driver_features = DRIVER_GEM |
> DRIVER_RENDER |
> @@ -1044,7 +1079,11 @@ static int add_gpu_components(struct device *dev,
>
> static int msm_drm_bind(struct device *dev)
> {
> - return msm_drm_init(dev, &msm_driver, NULL);
> + return msm_drm_init(dev,
> + msm_gpu_no_components() ?
> + &msm_kms_driver :
> + &msm_driver,
> + NULL);
> }
>
> static void msm_drm_unbind(struct device *dev)
> @@ -1080,9 +1119,11 @@ int msm_drv_probe(struct device *master_dev,
> return ret;
> }
>
> - ret = add_gpu_components(master_dev, &match);
> - if (ret)
> - return ret;
> + if (!msm_gpu_no_components()) {
> + ret = add_gpu_components(master_dev, &match);
> + if (ret)
> + return ret;
> + }
>
> /* on all devices that I am aware of, iommu's which can map
> * any address the cpu can see are used:
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index e7d8715bc61ccdee822bc6a1a0b0bbe7c8ff3552..1ff799f0c78133e73c6857e3692c2dca2c5e60fa 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -543,4 +543,6 @@ 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);
> +
> #endif /* __MSM_DRV_H__ */
>
> --
> 2.39.5
>
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