[PATCH libdrm v2] xf86drm: Parse the separate files to retrieve the vendor, ... info

[Emil Velikov]

From: Emil Velikov <emil.velikov at collabora.com>

Parsing config sysfs file wakes up the device. The latter of which may
be slow and isn't required to begin with.

Reading through config is/was required since the revision is not
available by other means, although with a kernel patch in the way that
is about to change.

Since returning 0 when one might expect a valid value is a no-go add a
workaround drmDeviceUseRevisionFile() which one can use to say "I don't
care if the revision file returns 0."

v2: Complete rework - add new API to control the method, instead of
changing it underneat the users' feet.

Cc: Michel Dänzer <michel.daenzer at amd.com>
Cc: Mauro Santos <registo.mailling at gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98502
Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
---
I don't have a strong preference for/against this or v1.

With this Mesa will require a 2 line patch. With v1 things will get
fixed magically, when rebuilt against newer libdrm.

Mauro I'll send the mesa patch in a second. Feel free to give it a spin.

Thanks
---
 xf86drm.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 xf86drm.h | 11 ++++++++++
 2 files changed, 78 insertions(+), 3 deletions(-)

diff --git a/xf86drm.c b/xf86drm.c
index 52add5e..676effc 100644
--- a/xf86drm.c
+++ b/xf86drm.c
@@ -113,6 +113,13 @@ void drmSetServerInfo(drmServerInfoPtr info)
     drm_server_info = info;
 }
 
+static bool use_revision_file;
+
+void drmDeviceUseRevisionFile(void)
+{
+    use_revision_file = true;
+}
+
 /**
  * Output a message to stderr.
  *
@@ -2946,10 +2953,56 @@ static int drmGetMaxNodeName(void)
            3 /* length of the node number */;
 }
 
-static int drmParsePciDeviceInfo(const char *d_name,
-                                 drmPciDeviceInfoPtr device)
-{
 #ifdef __linux__
+static int parse_separate_sysfs_files(const char *d_name,
+                                      drmPciDeviceInfoPtr device)
+{
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
+    static const char *attrs[] = {
+      "revision", /* XXX: make sure it's always first, see note below */
+      "vendor",
+      "device",
+      "subsystem_vendor",
+      "subsystem_device",
+    };
+    char path[PATH_MAX + 1];
+    unsigned int data[ARRAY_SIZE(attrs)];
+    FILE *fp;
+    int ret;
+
+    for (unsigned i = 0; i < ARRAY_SIZE(attrs); i++) {
+        snprintf(path, PATH_MAX, "/sys/class/drm/%s/device/%s",
+                 d_name, attrs[i]);
+        fp = fopen(path, "r");
+        if (!fp) {
+            /* Note: First we check the revision, since older kernels
+             * may not have it. Default to zero in such cases. */
+            if (i == 0) {
+                data[i] = 0;
+                continue;
+            }
+            return -errno;
+        }
+
+        ret = fscanf(fp, "%x", &data[i]);
+        fclose(fp);
+        if (ret != 1)
+            return -errno;
+
+    }
+
+    device->revision_id = data[0] & 0xff;
+    device->vendor_id = data[1] & 0xffff;
+    device->device_id = data[2] & 0xffff;
+    device->subvendor_id = data[3] & 0xffff;
+    device->subdevice_id = data[4] & 0xffff;
+
+    return 0;
+}
+
+static int parse_config_sysfs_file(const char *d_name,
+                                  drmPciDeviceInfoPtr device)
+{
     char path[PATH_MAX + 1];
     unsigned char config[64];
     int fd, ret;
@@ -2971,6 +3024,17 @@ static int drmParsePciDeviceInfo(const char *d_name,
     device->subdevice_id = config[46] | (config[47] << 8);
 
     return 0;
+}
+#endif
+
+static int drmParsePciDeviceInfo(const char *d_name,
+                                 drmPciDeviceInfoPtr device)
+{
+#ifdef __linux__
+    if (use_revision_file)
+        return parse_separate_sysfs_files(d_name, device);
+
+    return parse_config_sysfs_file(d_name, device);
 #else
 #warning "Missing implementation of drmParsePciDeviceInfo"
     return -EINVAL;
diff --git a/xf86drm.h b/xf86drm.h
index 481d882..d1ebc32 100644
--- a/xf86drm.h
+++ b/xf86drm.h
@@ -796,6 +796,17 @@ extern void drmFreeDevice(drmDevicePtr *device);
 extern int drmGetDevices(drmDevicePtr devices[], int max_devices);
 extern void drmFreeDevices(drmDevicePtr devices[], int count);
 
+
+/**
+ * Force any sequential calls to drmGetDevice/drmGetDevices to use the
+ * revision sysfs file instead of config one. The latter wakes up the device
+ * if powered off.
+ *
+ * A value of 0 will be returned for the revision_id field if the sysfs file
+ * is missing. DO NOT USE THIS if you depend on a correct revision_id.
+ */
+extern void drmDeviceUseRevisionFile(void);
+
 #if defined(__cplusplus)
 }
 #endif
-- 
2.10.2