I just wonder. What is drm-kmod way to handle the fact that drm device is a grandchild of pci bus? Does it store a device_t of vgapci* as dev->dev.bsddev member?

I think so. I think drm_device holds a pointer to a linux pci_dev, which has a dev.bsddev member pointing to the bsd pci device.

We have this code which takes care of that:

	if (pdrv != NULL && pdrv->isdrm) {
		parent = device_get_parent(dev);
		dinfo = device_get_ivars(parent);
		device_set_ivars(dev, dinfo);
	} else {

I think we need to do a simple cast here.

Style:
return (true);

I'm not sure I see what you mean. What part do you want to cast?

Are you talking about casting iter and passing it to for_each_sg_page to avoid code duplication?

I mean, how can we make this work w/o breaking any APIs?

Could we simply do:

#define sg_dma_page_iter sg_page_iter

We could, but it would require changing certain parts of drm to be FreeBSD specific, as they expect to be able to do sg_dma_page_iter->base.

https://github.com/amshafer/kms-drm/blob/drm-v5.1/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_buffer.c#L320

At the moment there are only two such cases in 5.1, but my guess is the number will increase over time and not decrease. Although casting the function argument isn't ideal, the current patch will allow future drm code to be imported unchanged.