On 02/03/2014 08:25 PM, David Herrmann wrote:
Hi
[..snip..]
Finally, support for probing GK20A is added in the last 2 patches. It should be
noted that contrary to what Nouveau currently expects, GK20A does not embed any
display hardware (that part being handled by tegradrm). So this driver should
really be only used through DRM render-nodes and collaborate with the display
driver using PRIME. I have not yet figured out how to turn GK20A's instantiation
of Nouveau into a render-node only driver without breaking support for existing
desktop GPUs, and consequently the driver spawns a /dev/dri/cardX node which we
should try to get rid of.
You cannot get rid of cardX currently. It is implied by DRIVER_MODESET
and that flag should actually be called NOT_A_LEGACY_DRIVER. So you
cannot remove it. I did try to replace DRIVER_MODESET by an inverted
DRIVER_LEGACY flag some time ago, but I thought it's not worth it.
Anyhow, you can easily add a new flag to make
drm_dev_register()/drm_dev_alloc() not create the drm_minor for
DRM_MINOR_LEGACY, which would prevent the card0 node from showing up.
But people started using the cardX interface as base interface so mesa
might not be able to open render-nodes if the related card-node is not
available (which is a bug in their code, so no reason to support that
by not adding stand-alone render-nodes).
Actually my mention of /dev/dri/cardX was misleading. I was rather
thinking about getting rid of the DRIVER_MODESET flag to correctly
expose what the card provides, not only to user-space, but to DRM
itself. The legacy node is ok as long as DRM itself correctly knows what
the driver can and cannot do and fails gracefully if the user tries to
set a mode.
DRIVER_MODESET is statically set in nouveau_drm.c, and the reason why I
cannot get rid of it is because the driver (and its features) is
registered with drm_pci_init() before the card is probed and its actual
features known.
For platform devices, you could check the card features before
registering it with drm_platform_init(), but then you have the issue
that the driver instance is referenced by every probed card, and thus
you cannot have cards with different capabilities.
So it seems like handling this would require the driver_features to move
from drm_driver to drm_device, but that's quite a core change. As
pointed out by you and Daniel, we can certainly live with the control
and legacy nodes. Nonetheless I'd be curious to know how (and if) this
case can be correctly handled.
Alex.
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