On 04/04/18 19:29, Laszlo Ersek wrote: > Hi Emil, > > On 04/03/18 19:13, Emil Velikov wrote: >> On 29 March 2018 at 12:17, Laszlo Ersek <lersek@xxxxxxxxxx> wrote: >>> On 03/28/18 16:35, Emil Velikov wrote: >>>> On 28 March 2018 at 11:27, Laszlo Ersek <lersek@xxxxxxxxxx> wrote: >>>>> On 03/28/18 03:24, Emil Velikov wrote: >>> >>>>>> Gents, can someone double-check this please? Just in case. >>>>> >>>>> I guess I should test whether this series regresses the use case >>>>> described in c2cbc38b97; is that correct? >>>>> >>>> Precisely. >>> >>>> [3] https://github.com/evelikov/linux/commits/ioctl-cleanups >>> >>> Unfortunately, this series seems to reintroduce the regression fixed >>> / described earlier in commit c2cbc38b97. >>> >> Thank you very much for testing. >> >> Believe I've tracked it down to a broken commit from 2014 ;-) >> Please try the following branch [1] - it's untested, but I'm 99% sure >> it will work like a charm. > > Alas, it does not work. I've done some more digging. Let me quote the commit message on the proposed patch again: > Ealier commit a325725633c26aa66ab940f762a6b0778edf76c0 did not attribute > that virtio can be either PCI or a platform device and removed the > .set_busid hook. Whereas only the "platform" instance should have been > removed. > > Since then, two things have happened: > - the driver manually calls drm_dev_set_unique, addressing the Xserver > regression - see commit 9785b4321b0bd701f8d21d3d3c676a7739a5cf22 > - core itself calls drm_pci_set_busid, on drm_set_busid IOCTL setting > the busid, so we don't need to fallback to dev->unique - see commit > 5c484cee7ef9c4fd29fa0ba09640d55960977145 > > With that in place we can remove the local workaround. This write-up of events is not precise enough. Instead, I think the timeline is as follows: (1) Commit a325725633c2 ("drm: Lobotomize set_busid nonsense for !pci drivers", 2016-06-21) introduced the regression. By removing drm_virtio_set_busid(), commit a325725633c2 changed the behavior of the following function: > static int drm_set_busid(struct drm_device *dev, struct drm_file *file_priv) > { > struct drm_master *master = file_priv->master; > int ret; > > if (master->unique != NULL) > drm_unset_busid(dev, master); > > if (dev->driver->set_busid) { > ret = dev->driver->set_busid(dev, master); > if (ret) { > drm_unset_busid(dev, master); > return ret; > } > } else { > WARN_ON(!dev->unique); > master->unique = kstrdup(dev->unique, GFP_KERNEL); > if (master->unique) > master->unique_len = strlen(dev->unique); > } > > return 0; > } When a325725633c2 removed drm_virtio_set_busid(), drm_set_busid() started taking the second branch, which wasn't doing the right thing for virtio-vga at the time. (2) There were two ways to fix the regression: either (a) return drm_set_busid() to taking the first branch, or (b) tweak the virtio-vga driver so that the second branch in drm_set_busid() start to behave right. My commit c2cbc38b9715 ("drm: virtio: reinstate drm_virtio_set_busid()", 2016-10-04) implemented (a), by reverting a few chunks of a325725633c2. (3) Gerd thought that approach (b) was superior (and I totally defer to him on this, now that I'm learning of his patches in the first place :) ). Namely, in commit 9785b4321b0b ("drm/virtio: fix busid regression", 2016-11-15), he implemented approach (b), and right after, in commit 1775db074a32 ("Revert "drm: virtio: reinstate drm_virtio_set_busid()"", 2016-11-15), he undid my commit c2cbc38b9715. In other words, Gerd replaced approach (a) with approach (b). (4) Subsequently, commit 5c484cee7ef9 ("drm: Remove drm_driver->set_busid hook", 2017-06-20), changed drm_set_busid() to the following: > static int drm_set_busid(struct drm_device *dev, struct drm_file *file_priv) > { > struct drm_master *master = file_priv->master; > int ret; > > if (master->unique != NULL) > drm_unset_busid(dev, master); > > if (dev_is_pci(dev->dev)) { > ret = drm_pci_set_busid(dev, master); > if (ret) { > drm_unset_busid(dev, master); > return ret; > } > } else { > WARN_ON(!dev->unique); > master->unique = kstrdup(dev->unique, GFP_KERNEL); > if (master->unique) > master->unique_len = strlen(dev->unique); > } > > return 0; > } Perhaps surprisingly, this change did not affect (or "help") virtio-vga at all, despite the fact that drm_virtio_set_busid() also used to call drm_pci_set_busid(). The reason for commit 5c484cee7ef9 not affecting virtio-vga is that the first branch would not be taken just the same, because dev_is_pci() returns false for virtio-vga. (So, the difference with drm_virtio_set_busid() is that drm_virtio_set_busid() would call drm_pci_set_busid() without checking dev_is_pci() first.) Here's the definition of the dev_is_pci() macro, from "include/linux/pci.h": > #define dev_is_pci(d) ((d)->bus == &pci_bus_type) However, the bus type for virtio-vga is "virtio_bus", not "pci_bus_type". Namely, virtio_pci_probe() [drivers/virtio/virtio_pci_common.c] calls register_virtio_device() [drivers/virtio/virtio.c], and there we have > int register_virtio_device(struct virtio_device *dev) > { > int err; > > dev->dev.bus = &virtio_bus; This means that post-5c484cee7ef9, we remain reliant on the second branch in drm_set_busid(), and therefore Gerd's commit 9785b4321b0b, from point (3), should not be backed out. What I could see as justified is a loud comment in drm_virtio_init(), just above the call to drm_dev_set_unique(), explaining why it is necessary to set "unique" manually. The reason is that virtio-vga technically has "virtio_bus", not "pci_bus_type", for bus type, and so the generic PCI BusID-setting will not cover it. Thanks Laszlo _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
