From b96e7972e90144a697401f393ae8e1e12b3e767c Mon Sep 17 00:00:00 2001
From: Adam Jackson <ajax@redhat.com>
Date: Tue, 18 Sep 2018 14:37:51 -0400
Subject: [PATCH] linux: Make platform device probe less fragile

If we have platform devices - and we usually do - we would really want
them to bind through the platform bus code not PCI. At the point where
get_drm_info runs, however, we haven't yet taken our own VT, which means
we can't perform drm "master" operations on the device. This is tragic,
because the operation we need to perform here is fishing the bus id out
of the kernel, which we can only do after drmSetInterfaceVersion, which
for some reason stores that knowledge on the device not the file handle
and thus needs master access. Since we fail, the probe logic gets very
confused.

Fortunately we know the format of the busid string (it's our own, drm
copied it from xfree86), so we can scrape that out of the sysfs path. We
do still potentially do the whole SetInterfaceVersion dance later on,
but it's harmless at that point because we've taken the VT by then.

This should all be vastly simplified, but that is not the cat we're
skinning today.
---
 hw/xfree86/os-support/linux/lnx_platform.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/hw/xfree86/os-support/linux/lnx_platform.c b/hw/xfree86/os-support/linux/lnx_platform.c
index 70374ac..cbf7dd2 100644
--- a/hw/xfree86/os-support/linux/lnx_platform.c
+++ b/hw/xfree86/os-support/linux/lnx_platform.c
@@ -29,6 +29,9 @@ get_drm_info(struct OdevAttributes *attribs, char *path, int delayed_index)
     int fd;
     int err = 0;
     Bool paused, server_fd = FALSE;
+    const char pci_prefix[] = "/sys/devices/pci";
+
+    LogMessage(X_INFO, "Platform probe for %s\n", attribs->syspath);
 
     fd = systemd_logind_take_fd(attribs->major, attribs->minor, path, &paused);
     if (fd != -1) {
@@ -53,13 +56,6 @@ get_drm_info(struct OdevAttributes *attribs, char *path, int delayed_index)
     sv.drm_dd_major = -1;       /* Don't care */
     sv.drm_dd_minor = -1;       /* Don't care */
 
-    err = drmSetInterfaceVersion(fd, &sv);
-    if (err) {
-        xf86Msg(X_ERROR, "%s: failed to set DRM interface version 1.4: %s\n",
-                path, strerror(-err));
-        goto out;
-    }
-
     /* for a delayed probe we've already added the device */
     if (delayed_index == -1) {
             xf86_add_platform_device(attribs, FALSE);
@@ -69,9 +65,15 @@ get_drm_info(struct OdevAttributes *attribs, char *path, int delayed_index)
     if (server_fd)
         xf86_platform_devices[delayed_index].flags |= XF86_PDEV_SERVER_FD;
 
-    buf = drmGetBusid(fd);
-    xf86_platform_odev_attributes(delayed_index)->busid = XNFstrdup(buf);
-    drmFreeBusid(buf);
+    /* parse out a bus id */
+    if (!strncmp(attribs->syspath, pci_prefix, strlen(pci_prefix))) {
+        char *dbdf = attribs->syspath + strlen(pci_prefix) + strlen("XXXX:XX") + 1;
+        asprintf(&xf86_platform_odev_attributes(delayed_index)->busid,
+                 "pci:%.12s", dbdf);
+        LogMessage(X_INFO, "Platform PCI device at %s\n",
+                   xf86_platform_odev_attributes(delayed_index)->busid);
+    }
+
 
     v = drmGetVersion(fd);
     if (!v) {
-- 
2.17.1