mfd: core: Make a best effort attempt to match devices with the correct of_nodes

Currently, when a child platform device (sometimes referred to as a sub-device) is registered via the Multi-Functional Device (MFD) API, the framework attempts to match the newly registered platform device with its associated Device Tree (OF) node. Until now, the device has been allocated the first node found with an identical OF compatible string. Unfortunately, if there are, say for example '3' devices which are to be handled by the same driver and therefore have the same compatible string, each of them will be allocated a pointer to the *first* node. An example Device Tree entry might look like this: mfd_of_test { compatible = "mfd,of-test-parent"; #address-cells = <0x02>; #size-cells = <0x02>; child@aaaaaaaaaaaaaaaa { compatible = "mfd,of-test-child"; reg = <0xaaaaaaaa 0xaaaaaaaa 0 0x11>, <0xbbbbbbbb 0xbbbbbbbb 0 0x22>; }; child@cccccccc { compatible = "mfd,of-test-child"; reg = <0x00000000 0xcccccccc 0 0x33>; }; child@dddddddd00000000 { compatible = "mfd,of-test-child"; reg = <0xdddddddd 0x00000000 0 0x44>; }; }; When used with example sub-device registration like this: static const struct mfd_cell mfd_of_test_cell[] = { OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 0, "mfd,of-test-child"), OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child"), OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child") }; ... the current implementation will result in all devices being allocated the first OF node found containing a matching compatible string: [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0 [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@aaaaaaaaaaaaaaaa [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1 [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@aaaaaaaaaaaaaaaa [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2 [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@aaaaaaaaaaaaaaaa After this patch each device will be allocated a unique OF node: [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0 [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@aaaaaaaaaaaaaaaa [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1 [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@cccccccc [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2 [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@dddddddd00000000 Which is fine if all OF nodes are identical. However if we wish to apply an attribute to particular device, we really need to ensure the correct OF node will be associated with the device containing the correct address. We accomplish this by matching the device's address expressed in DT with one provided during sub-device registration. Like this: static const struct mfd_cell mfd_of_test_cell[] = { OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child", 0xdddddddd00000000), OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child", 0xaaaaaaaaaaaaaaaa), OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 3, "mfd,of-test-child", 0x00000000cccccccc) }; This will ensure a specific device (designated here using the platform_ids; 1, 2 and 3) is matched with a particular OF node: [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0 [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@dddddddd00000000 [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1 [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@aaaaaaaaaaaaaaaa [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2 [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@cccccccc This implementation is still not infallible, hence the mention of "best effort" in the commit subject. Since we have not *insisted* on the existence of 'reg' properties (in some scenarios they just do not make sense) and no device currently uses the new 'of_reg' attribute, we have to make an on-the-fly judgement call whether to associate the OF node anyway. Which we do in cases where parent drivers haven't specified a particular OF node to match to. So there is a *slight* possibility of the following result (note: the implementation here is convoluted, but it shows you one means by which this process can still break): /* * First entry will match to the first OF node with matching compatible * Second will fail, since the first took its OF node and is no longer available * Third will succeed */ static const struct mfd_cell mfd_of_test_cell[] = { OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child"), OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child", 0xaaaaaaaaaaaaaaaa), OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 3, "mfd,of-test-child", 0x00000000cccccccc) }; The result: [0.753869] mfd-of-test-parent mfd_of_test: Registering 3 devices [0.756597] mfd-of-test-child: Failed to locate of_node [id: 2] [0.759999] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1 [0.760314] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@aaaaaaaaaaaaaaaa [0.760908] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2 [0.761183] mfd-of-test-child mfd-of-test-child.2: No OF node associated with this device [0.761621] mfd-of-test-child mfd-of-test-child.3: Probing platform device: 3 [0.761899] mfd-of-test-child mfd-of-test-child.3: Using OF node: child@cccccccc We could code around this with some pre-parsing semantics, but the added complexity required to cover each and every corner-case is not justified. Merely patching the current failing (via this patch) is already working with some pretty small corner-cases. Other issues should be patched in the parent drivers which can be achieved simply by implementing OF_MFD_CELL_REG().

LJLee Jones committed 6 years ago