The driver core/bus adding supplier-consumer dependencies by default enables functional dependencies to be tracked correctly even when the consumer devices haven't had their drivers registered or loaded (if they are modules). However, when the bus incorrectly adds dependencies that it shouldn't have added, the devices might never probe. For example, if device-C is a consumer of device-S and they have phandles to each other in DT, the following could happen: 1. Device-S get added first. 2. The bus add_links() callback will (incorrectly) try to link it as a consumer of device-C. 3. Since device-C isn't present, device-S will be put in "waiting-for-supplier" list. 4. Device-C gets added next. 5. All devices in "waiting-for-supplier" list are retried for linking. 6. Device-S gets linked as consumer to Device-C. 7. The bus add_links() callback will (correctly) try to link it as a consumer of device-S. 8. This isn't allowed because it would create a cyclic device links. Neither devices will get probed since the supplier is marked as dependent on the consumer. And the consumer will never probe because the consumer can't get resources from the supplier. Without this patch, things stay in this broken state. However, with this patch, the execution will continue like this: 9. Device-C's driver is loaded. 10. Device-C's driver removes Device-S as a consumer of Device-C. 11. Device-C's driver adds Device-C as a consumer of Device-S. 12. Device-S probes. 14. Device-C probes. kbuild test robot reported missing documentation for device.has_edit_links Reported-by: kbuild test robot <lkp@intel.com> Signed-off-by: Saravana Kannan <saravanak@google.com> Link: https://lore.kernel.org/r/20190731221721.187713-3-saravanak@google.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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| @@ -349,6 +349,20 @@ enum probe_type { · 348 unmodified lines | ||
| 349 | 349 | * @probe_type: Type of the probe (synchronous or asynchronous) to use. |
| 350 | 350 | * @of_match_table: The open firmware table. |
| 351 | 351 | * @acpi_match_table: The ACPI match table. |
| 352 | + * @edit_links: Called to allow a matched driver to edit the device links the | |
| 353 | + * bus might have added incorrectly. This will be useful to handle | |
| 354 | + * cases where the bus incorrectly adds functional dependencies | |
| 355 | + * that aren't true or tries to create cyclic dependencies. But | |
| 356 | + * doesn't correctly handle functional dependencies that are | |
| 357 | + * missed by the bus as the supplier's sync_state might get to | |
| 358 | + * execute before the driver for a missing consumer is loaded and | |
| 359 | + * gets to edit the device links for the consumer. | |
| 360 | + * | |
| 361 | + * This function might be called multiple times after a new device | |
| 362 | + * is added. The function is expected to create all the device | |
| 363 | + * links for the new device and return 0 if it was completed | |
| 364 | + * successfully or return an error if it needs to be reattempted | |
| 365 | + * in the future. | |
| 352 | 366 | * @probe: Called to query the existence of a specific device, |
| 353 | 367 | * whether this driver can work with it, and bind the driver |
| 354 | 368 | * to a specific device. |
| @@ -388,6 +402,7 @@ struct device_driver { · 33 unmodified lines | ||
| 388 | 402 | const struct of_device_id *of_match_table; |
| 389 | 403 | const struct acpi_device_id *acpi_match_table; |
| 390 | 404 | |
| 405 | + int (*edit_links)(struct device *dev); | |
| 391 | 406 | int (*probe) (struct device *dev); |
| 392 | 407 | int (*remove) (struct device *dev); |
| 393 | 408 | void (*shutdown) (struct device *dev); |
| @@ -1220,6 +1235,8 @@ struct dev_links_info { · 826 unmodified lines | ||
| 1220 | 1235 | * @offline: Set after successful invocation of bus type's .offline(). |
| 1221 | 1236 | * @of_node_reused: Set if the device-tree node is shared with an ancestor |
| 1222 | 1237 | * device. |
| 1238 | + * @has_edit_links: This device has a driver than is capable of | |
| 1239 | + * editing the device links created by driver core. | |
| 1223 | 1240 | * @dma_coherent: this particular device is dma coherent, even if the |
| 1224 | 1241 | * architecture supports non-coherent devices. |
| 1225 | 1242 | * |
| @@ -1313,6 +1330,7 @@ struct device { · 87 unmodified lines | ||
| 1313 | 1330 | bool offline_disabled:1; |
| 1314 | 1331 | bool offline:1; |
| 1315 | 1332 | bool of_node_reused:1; |
| 1333 | + bool has_edit_links:1; | |
| 1316 | 1334 | #if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \ |
| 1317 | 1335 | defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \ |
| 1318 | 1336 | defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL) |
| @@ -1564,6 +1582,7 @@ extern int __must_check device_attach(struct device *dev); · 245 unmodified lines | ||
| 1564 | 1582 | extern int __must_check driver_attach(struct device_driver *drv); |
| 1565 | 1583 | extern void device_initial_probe(struct device *dev); |
| 1566 | 1584 | extern int __must_check device_reprobe(struct device *dev); |
| 1585 | +extern int driver_edit_links(struct device *dev); | |
| 1567 | 1586 | |
| 1568 | 1587 | extern bool device_is_bound(struct device *dev); |
| 1569 | 1588 | |
| @@ -1654,6 +1673,7 @@ struct device_link *device_link_add(struct device *consumer, · 84 unmodified lines | ||
| 1654 | 1673 | struct device *supplier, u32 flags); |
| 1655 | 1674 | void device_link_del(struct device_link *link); |
| 1656 | 1675 | void device_link_remove(void *consumer, struct device *supplier); |
| 1676 | +void device_link_remove_from_wfs(struct device *consumer); | |
| 1657 | 1677 | |
| 1658 | 1678 | #ifndef dev_fmt |
| 1659 | 1679 | #define dev_fmt(fmt) fmt |