Re: [PATCH] drm/amdgpu: Add 'modeset' module parameter

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Hi

Am 11.05.22 um 20:19 schrieb Lyude Paul:
Many DRM drivers feature a 'modeset' argument, which can be used to
enable/disable the entire driver (as opposed to passing nomodeset to the
kernel, which would disable modesetting globally and make it difficult to
load amdgpu afterwards). Apparently amdgpu is actually missing this
however, so let's add it!

We have recently consolidated the handling of the modeset parameter in the macro drm_module_pci_driver_if_modeset(), [1] which has a deprecation warning in the docs. Only a few older drivers use modeset and we don't want to use it further.

Better alternatives are nomodeset or initcall_blacklist=amdgpu_init.

Best regards
Thomas

[1] https://cgit.freedesktop.org/drm/drm-tip/tree/include/drm/drm_module.h#n79


Keep in mind that this currently just lets one enable or disable amdgpu, I
haven't bothered adding a headless mode like nouveau has - however I'm sure
someone else can add this if needed.

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index ebd37fb19cdb..24e6fb4517cc 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -872,6 +872,15 @@ MODULE_PARM_DESC(smu_pptable_id,
  	"specify pptable id to be used (-1 = auto(default) value, 0 = use pptable from vbios, > 0 = soft pptable id)");
  module_param_named(smu_pptable_id, amdgpu_smu_pptable_id, int, 0444);
+/**
+ * DOC: modeset (int)
+ * Used to enable/disable modesetting for amdgpu exclusively.
+ */
+bool amdgpu_enable_modeset = true;
+MODULE_PARM_DESC(modeset,
+		 "Enable or disable display driver (1 = on (default), 0 = off");
+module_param_named(modeset, amdgpu_enable_modeset, bool, 0444);
+
  /* These devices are not supported by amdgpu.
   * They are supported by the mach64, r128, radeon drivers
   */
@@ -2003,6 +2012,11 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
  	bool is_fw_fb;
  	resource_size_t base, size;
+ if (!amdgpu_enable_modeset) {
+		DRM_INFO("modeset=0 passed to amdgpu, driver will not be enabled\n");
+		return -ENODEV;
+	}
+
  	/* skip devices which are owned by radeon */
  	for (i = 0; i < ARRAY_SIZE(amdgpu_unsupported_pciidlist); i++) {
  		if (amdgpu_unsupported_pciidlist[i] == pdev->device)

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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