Re: non-PCI driver name lookup

[Robert Swindells <rjs%fdy2.co.uk@localhost>]

I wrote:
>On 2019-07-09 14:23, maya%netbsd.org@localhost wrote:
>> On Tue, Jul 09, 2019 at 11:07:37AM +0100, Robert Swindells wrote:
>>> 
>>> maya%netbsd.org@localhost wrote:
>>> >On Sun, Jul 07, 2019 at 11:23:14PM +0100, Robert Swindells wrote:
>>> >>
>>> >> The pinebook uses the modesetting X11 driver.
>>> >>
>>> >> An application that calls DRI2Connect() doesn't get back valid values
>>> >> for device name and driver name so typically assumes that DRI2 isn't
>>> >> available.
>>> >>
>>> >> This looks to be down to how libdrm tries to work out which driver is
>>> >> being used from an open file descriptor. I presume the NetBSD specific
>>> >> code in it does work for PCI devices but it looks like we need to add
>>> >> something for display devices that are built into the CPU.
>>> >
>>> >I assume, although I can't find proof that it's the case, that you want
>>> >to adjust the 'unique' value.
>>> >
>>> >arm/nvidia/tegra_nouveau.c
>>> >257:	master->unique = kmem_asprintf("platform:tegra_nouveau:%02d", id);
>>> 
>>> The 'unique' value ought to be fine, there is code in
>>> arm/sunxi/sunxi_drm.c to create it, but it never gets called.
>>> 
>>> >I think the code in libdrm looks at this value via DRM_IOCTL_GET_UNIQUE,
>>> >but I'm not sure.
>>> 
>>> It does, and creation of the unique value should be done lazily from
>>> the DRM_IOCTL_SET_VERSION ioctl. This ioctl fails as the is_master
>>> member of the file struct for the drm device isn't set. Not got any
>>> further in tracking down why.
>>> 
>>> 
>> 
>> You might find the description here useful,
>> https://github.com/coypoop/drm/blob/maya-drm51/sys/external/bsd/drm2/dist/drm/drm_ioctl.c#L79-L99
>
>That doesn't match what libdrm is actually doing.

It might be better to say that libdrm when called from typical
applications isn't doing what is described in that comment.

I don't think that applications or higher level libraries should need to
work out whether they are connecting to a PCI graphics device or
something else and to call different libdrm functions to work with it.

I'm testing this with multimedia/libva-utils and multimedia/libva,
running 'vainfo' should be able to get back 'sunxi' as the name of
the DRI2 device in use on the pinebook, then fail because there isn't
yet a libva driver for it.