@@ -3099,6 +3099,10 @@ int num_ioctls;</synopsis>
<!-- External: render nodes -->
<sect1>
+ <title>libdrm Device Lookup</title>
+!Pdrivers/gpu/drm/drm_vma_manager.c getunique and setversion story
+ </sect1>
+ <sect1>
<title>Render nodes</title>
<para>
DRM core provides multiple character-devices for user-space to use.
@@ -189,7 +189,6 @@ static struct drm_driver armada_drm_driver = {
.load = armada_drm_load,
.lastclose = armada_drm_lastclose,
.unload = armada_drm_unload,
- .set_busid = drm_platform_set_busid,
.get_vblank_counter = drm_vblank_no_hw_counter,
.enable_vblank = armada_drm_enable_vblank,
.disable_vblank = armada_drm_disable_vblank,
@@ -37,6 +37,64 @@
#include <linux/pci.h>
#include <linux/export.h>
+/**
+ * DOC: getunique and setversion story
+ *
+ * BEWARE THE DRAGONS! MIND THE TRAPDOORS!
+ *
+ * In and attempt to warn anyone else who's trying to figure out what's going
+ * on here, I'll try to summarize the story. First things first, let's clear up
+ * the names, because the kernel internals, libdrm and the ioctls are all named
+ * differently:
+ *
+ * - GET_UNIQUE ioctl, implemented by drm_getunique is wrapped up in libdrm
+ * through the drmGetBusid function.
+ * - The libdrm drmSetBusid function is backed by the SET_UNIQUE ioctl. All
+ * that code is nerved in the kernel with drm_invalid_op().
+ * - The internal set_busid kernel functions and driver callbacks are
+ * exclusively use by the SET_VERSION ioctl, because only drm 1.0 (which is
+ * nerved) allowed userspace to set the busid through the above ioctl.
+ * - Other ioctls and functions involved are named consistently.
+ *
+ * For anyone wondering what's the difference between drm 1.1 and 1.4: Correctly
+ * handling pci domains in the busid on ppc. Doing this correctly was only
+ * implemented in libdrm in 2010, hence can't be nerved yet. No one knows what's
+ * special with drm 1.2 and 1.3.
+ *
+ * Now the actual horror story of how device lookup in drm works. At large,
+ * there's 2 different ways, either by busid, or by device driver name.
+ *
+ * Opening by busid is fairly simple:
+ *
+ * 1. First call SET_VERSION to make sure pci domains are handled properly. As a
+ * side-effect this fills out the unique name in the master structure.
+ * 2. Call GET_UNIQUE to read out the unique name from the master structure,
+ * which matches the busid thanks to step 1. If it doesn't, proceed to try
+ * the next device node.
+ *
+ * Opening by name is slightly different:
+ *
+ * 1. Directly call VERSION to get the version and to match against the driver
+ * name returned by that ioctl. Note that SET_VERSION is not called, which
+ * means the the unique name for the master node just opening is _not_ filled
+ * out. This despite that with current drm device nodes are always bound to
+ * one device, and can't be runtime assigned like with drm 1.0.
+ * 2. Match driver name. If it mismatches, proceed to the next device node.
+ * 3. Call GET_UNIQUE, and check whether the unique name has length zero (by
+ * checking that the first byte in the string is 0). If that's not the case
+ * libdrm skips and proceeds to the next device node. Probably this is just
+ * copypasta from drm 1.0 times where a set unique name meant that the driver
+ * was in use already, but that's just conjecture.
+ *
+ * Long story short: To keep the open by name logic working, GET_UNIQUE must
+ * _not_ return a unique string when SET_VERSION hasn't been called yet,
+ * otherwise libdrm breaks. Even when that unique string can't ever change, and
+ * is totally irrelevant for actually opening the device because runtime
+ * assignable device instances were only support in drm 1.0, which is long dead.
+ * But the libdrm code in drmOpenByName somehow survived, hence this can't be
+ * broken.
+ */
+
static int drm_version(struct drm_device *dev, void *data,
struct drm_file *file_priv);
@@ -68,24 +68,6 @@ err_free:
return ret;
}
-int drm_platform_set_busid(struct drm_device *dev, struct drm_master *master)
-{
- int id;
-
- id = dev->platformdev->id;
- if (id < 0)
- id = 0;
-
- master->unique = kasprintf(GFP_KERNEL, "platform:%s:%02d",
- dev->platformdev->name, id);
- if (!master->unique)
- return -ENOMEM;
-
- master->unique_len = strlen(master->unique);
- return 0;
-}
-EXPORT_SYMBOL(drm_platform_set_busid);
-
/**
* drm_platform_init - Register a platform device with the DRM subsystem
* @driver: DRM device driver
@@ -496,7 +496,6 @@ static struct drm_driver etnaviv_drm_driver = {
DRIVER_RENDER,
.open = etnaviv_open,
.preclose = etnaviv_preclose,
- .set_busid = drm_platform_set_busid,
.gem_free_object_unlocked = etnaviv_gem_free_object,
.gem_vm_ops = &vm_ops,
.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
@@ -407,7 +407,6 @@ static struct drm_driver exynos_drm_driver = {
.preclose = exynos_drm_preclose,
.lastclose = exynos_drm_lastclose,
.postclose = exynos_drm_postclose,
- .set_busid = drm_platform_set_busid,
.get_vblank_counter = drm_vblank_no_hw_counter,
.enable_vblank = exynos_drm_crtc_enable_vblank,
.disable_vblank = exynos_drm_crtc_disable_vblank,
@@ -171,7 +171,6 @@ static struct drm_driver kirin_drm_driver = {
.driver_features = DRIVER_GEM | DRIVER_MODESET | DRIVER_PRIME |
DRIVER_ATOMIC | DRIVER_HAVE_IRQ,
.fops = &kirin_drm_fops,
- .set_busid = drm_platform_set_busid,
.gem_free_object_unlocked = drm_gem_cma_free_object,
.gem_vm_ops = &drm_gem_cma_vm_ops,
@@ -407,7 +407,6 @@ static struct drm_driver imx_drm_driver = {
.load = imx_drm_driver_load,
.unload = imx_drm_driver_unload,
.lastclose = imx_drm_driver_lastclose,
- .set_busid = drm_platform_set_busid,
.gem_free_object_unlocked = drm_gem_cma_free_object,
.gem_vm_ops = &drm_gem_cma_vm_ops,
.dumb_create = drm_gem_cma_dumb_create,
@@ -722,7 +722,6 @@ static struct drm_driver msm_driver = {
.open = msm_open,
.preclose = msm_preclose,
.lastclose = msm_lastclose,
- .set_busid = drm_platform_set_busid,
.irq_handler = msm_irq,
.irq_preinstall = msm_irq_preinstall,
.irq_postinstall = msm_irq_postinstall,
@@ -1070,7 +1070,6 @@ nouveau_drm_init(void)
driver_pci = driver_stub;
driver_pci.set_busid = drm_pci_set_busid;
driver_platform = driver_stub;
- driver_platform.set_busid = drm_platform_set_busid;
nouveau_display_options();
@@ -801,7 +801,6 @@ static struct drm_driver omap_drm_driver = {
.unload = dev_unload,
.open = dev_open,
.lastclose = dev_lastclose,
- .set_busid = drm_platform_set_busid,
.get_vblank_counter = drm_vblank_no_hw_counter,
.enable_vblank = omap_irq_enable_vblank,
.disable_vblank = omap_irq_disable_vblank,
@@ -259,7 +259,6 @@ static struct drm_driver shmob_drm_driver = {
| DRIVER_PRIME,
.load = shmob_drm_load,
.unload = shmob_drm_unload,
- .set_busid = drm_platform_set_busid,
.irq_handler = shmob_drm_irq,
.get_vblank_counter = drm_vblank_no_hw_counter,
.enable_vblank = shmob_drm_enable_vblank,
@@ -541,7 +541,6 @@ static struct drm_driver tilcdc_driver = {
.load = tilcdc_load,
.unload = tilcdc_unload,
.lastclose = tilcdc_lastclose,
- .set_busid = drm_platform_set_busid,
.irq_handler = tilcdc_irq,
.irq_preinstall = tilcdc_irq_preinstall,
.irq_postinstall = tilcdc_irq_postinstall,
@@ -27,16 +27,6 @@
#include "virtgpu_drv.h"
-int drm_virtio_set_busid(struct drm_device *dev, struct drm_master *master)
-{
- struct pci_dev *pdev = dev->pdev;
-
- if (pdev) {
- return drm_pci_set_busid(dev, master);
- }
- return 0;
-}
-
static void virtio_pci_kick_out_firmware_fb(struct pci_dev *pci_dev)
{
struct apertures_struct *ap;
@@ -117,7 +117,6 @@ static const struct file_operations virtio_gpu_driver_fops = {
static struct drm_driver driver = {
.driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_PRIME | DRIVER_RENDER | DRIVER_ATOMIC,
- .set_busid = drm_virtio_set_busid,
.load = virtio_gpu_driver_load,
.unload = virtio_gpu_driver_unload,
.open = virtio_gpu_driver_open,
@@ -49,7 +49,6 @@
#define DRIVER_PATCHLEVEL 1
/* virtgpu_drm_bus.c */
-int drm_virtio_set_busid(struct drm_device *dev, struct drm_master *master);
int drm_virtio_init(struct drm_driver *driver, struct virtio_device *vdev);
struct virtio_gpu_object {
@@ -1128,7 +1128,6 @@ extern int drm_pcie_get_max_link_width(struct drm_device *dev, u32 *mlw);
/* platform section */
extern int drm_platform_init(struct drm_driver *driver, struct platform_device *platform_device);
-extern int drm_platform_set_busid(struct drm_device *d, struct drm_master *m);
/* returns true if currently okay to sleep */
static __inline__ bool drm_can_sleep(void)