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Diffstat (limited to 'doc/driver-model/design.rst')
| -rw-r--r-- | doc/driver-model/design.rst | 179 |
1 files changed, 95 insertions, 84 deletions
diff --git a/doc/driver-model/design.rst b/doc/driver-model/design.rst index 96525b6ccc..ffed7d5f79 100644 --- a/doc/driver-model/design.rst +++ b/doc/driver-model/design.rst @@ -59,7 +59,7 @@ uclass: The demo class is pretty simple, but not trivial. The intention is that it can be used for testing, so it will implement all driver model features and provide good code coverage of them. It does have multiple drivers, it -handles parameter data and platdata (data which tells the driver how +handles parameter data and plat (data which tells the driver how to operate on a particular platform) and it uses private driver data. To try it, see the example session below:: @@ -282,7 +282,7 @@ in drivers/demo/demo-simple.c: static int simple_hello(struct udevice *dev, int ch) { - const struct dm_demo_pdata *pdata = dev_get_platdata(dev); + const struct dm_demo_pdata *pdata = dev_get_plat(dev); printf("Hello from %08x: %s %d\n", map_to_sysmem(dev), pdata->colour, pdata->sides); @@ -333,11 +333,11 @@ Briefly, they are: * bind - make the driver model aware of a device (bind it to its driver) * unbind - make the driver model forget the device - * ofdata_to_platdata - convert device tree data to platdata - see later + * of_to_plat - convert device tree data to plat - see later * probe - make a device ready for use * remove - remove a device so it cannot be used until probed again -The sequence to get a device to work is bind, ofdata_to_platdata (if using +The sequence to get a device to work is bind, of_to_plat (if using device tree) and probe. @@ -396,7 +396,7 @@ The data can be interpreted by the drivers however they like - it is basically a communication scheme between the board-specific code and the generic drivers, which are intended to work on any board. -Drivers can access their data via dev->info->platdata. Here is +Drivers can access their data via dev->info->plat. Here is the declaration for the platform data, which would normally appear in the board file. @@ -410,7 +410,7 @@ in the board file. static const struct driver_info info[] = { { .name = "demo_shape_drv", - .platdata = &red_square, + .plat = &red_square, }, }; @@ -420,9 +420,9 @@ in the board file. Device Tree ----------- -While platdata is useful, a more flexible way of providing device data is +While plat is useful, a more flexible way of providing device data is by using device tree. In U-Boot you should use this where possible. Avoid -sending patches which make use of the U_BOOT_DEVICE() macro unless strictly +sending patches which make use of the U_BOOT_DRVINFO() macro unless strictly necessary. With device tree we replace the above code with the following device tree @@ -436,7 +436,7 @@ fragment: sides = <4>; }; -This means that instead of having lots of U_BOOT_DEVICE() declarations in +This means that instead of having lots of U_BOOT_DRVINFO() declarations in the board file, we put these in the device tree. This approach allows a lot more generality, since the same board file can support many types of boards (e,g. with the same SoC) just by using different device trees. An added @@ -448,24 +448,24 @@ The easiest way to make this work it to add a few members to the driver: .. code-block:: c - .platdata_auto_alloc_size = sizeof(struct dm_test_pdata), - .ofdata_to_platdata = testfdt_ofdata_to_platdata, + .plat_auto = sizeof(struct dm_test_pdata), + .of_to_plat = testfdt_of_to_plat, -The 'auto_alloc' feature allowed space for the platdata to be allocated -and zeroed before the driver's ofdata_to_platdata() method is called. The -ofdata_to_platdata() method, which the driver write supplies, should parse -the device tree node for this device and place it in dev->platdata. Thus +The 'auto' feature allowed space for the plat to be allocated +and zeroed before the driver's of_to_plat() method is called. The +of_to_plat() method, which the driver write supplies, should parse +the device tree node for this device and place it in dev->plat. Thus when the probe method is called later (to set up the device ready for use) the platform data will be present. -Note that both methods are optional. If you provide an ofdata_to_platdata +Note that both methods are optional. If you provide an of_to_plat method then it will be called first (during activation). If you provide a probe method it will be called next. See Driver Lifecycle below for more details. -If you don't want to have the platdata automatically allocated then you -can leave out platdata_auto_alloc_size. In this case you can use malloc -in your ofdata_to_platdata (or probe) method to allocate the required memory, +If you don't want to have the plat automatically allocated then you +can leave out plat_auto. In this case you can use malloc +in your of_to_plat (or probe) method to allocate the required memory, and you should free it in the remove method. The driver model tree is intended to mirror that of the device tree. The @@ -515,11 +515,23 @@ cases. While it might be tempting to automatically renumber the devices where there are gaps in the sequence, this can lead to confusion and is not the way that U-Boot works. -Each device can request a sequence number. If none is required then the -device will be automatically allocated the next available sequence number. +Where a device gets its sequence number is controlled by the DM_SEQ_ALIAS +Kconfig option, which can have a different value in U-Boot proper and SPL. +If this option is not set, aliases are ignored. -To specify the sequence number in the device tree an alias is typically -used. Make sure that the uclass has the DM_UC_FLAG_SEQ_ALIAS flag set. +Even if CONFIG_DM_SEQ_ALIAS is enabled, the uclass must still have the +DM_UC_FLAG_SEQ_ALIAS flag set, for its devices to be sequenced by aliases. + +With those options set, devices with an alias (e.g. "serial2") will get that +sequence number (e.g. 2). Other devices get the next available number after all +aliases and all existing numbers. This means that if there is just a single +alias "serial2", unaliased serial devices will be assigned 3 or more, with 0 and +1 being unused. + +If CONFIG_DM_SEQ_ALIAS or DM_UC_FLAG_SEQ_ALIAS are not set, all devices will get +sequence numbers in a simple ordering starting from 0. To find the next number +to allocate, driver model scans through to find the maximum existing number, +then uses the next one. It does not attempt to fill in gaps. .. code-block:: none @@ -546,12 +558,18 @@ More commonly you can use node references, which expand to the full path: The alias resolves to the same string in this case, but this version is easier to read. -Device sequence numbers are resolved when a device is probed. Before then -the sequence number is only a request which may or may not be honoured, -depending on what other devices have been probed. However the numbering is -entirely under the control of the board author so a conflict is generally -an error. +Device sequence numbers are resolved when a device is bound and the number does +not change for the life of the device. + +There are some situations where the uclass must allocate sequence numbers, +since a strictly increase sequence (with devicetree nodes bound first) is not +suitable. An example of this is the PCI bus. In this case, you can set the +uclass DM_UC_FLAG_NO_AUTO_SEQ flag. With this flag set, only devices with an +alias will be assigned a number by driver model. The rest is left to the uclass +to sort out, e.g. when enumerating the bus. +Note that changing the sequence number for a device (e.g. in a driver) is not +permitted. If it is felt to be necessary, ask on the mailing list. Bus Drivers ----------- @@ -587,9 +605,9 @@ Each of the devices is connected to a different address on the USB bus. The bus device wants to store this address and some other information such as the bus speed for each device. -To achieve this, the bus device can use dev->parent_platdata in each of its +To achieve this, the bus device can use dev->parent_plat in each of its three children. This can be auto-allocated if the bus driver (or bus uclass) -has a non-zero value for per_child_platdata_auto_alloc_size. If not, then +has a non-zero value for per_child_plat_auto. If not, then the bus device or uclass can allocate the space itself before the child device is probed. @@ -647,32 +665,36 @@ Bind stage U-Boot discovers devices using one of these two methods: -- Scan the U_BOOT_DEVICE() definitions. U-Boot looks up the name specified +- Scan the U_BOOT_DRVINFO() definitions. U-Boot looks up the name specified by each, to find the appropriate U_BOOT_DRIVER() definition. In this case, - there is no path by which driver_data may be provided, but the U_BOOT_DEVICE() - may provide platdata. + there is no path by which driver_data may be provided, but the U_BOOT_DRVINFO() + may provide plat. - Scan through the device tree definitions. U-Boot looks at top-level nodes in the the device tree. It looks at the compatible string in each node and uses the of_match table of the U_BOOT_DRIVER() structure to find the right driver for each node. In this case, the of_match table may provide a - driver_data value, but platdata cannot be provided until later. + driver_data value, but plat cannot be provided until later. For each device that is discovered, U-Boot then calls device_bind() to create a new device, initializes various core fields of the device object such as name, uclass & driver, initializes any optional fields of the device object that are -applicable such as of_offset, driver_data & platdata, and finally calls the +applicable such as of_offset, driver_data & plat, and finally calls the driver's bind() method if one is defined. At this point all the devices are known, and bound to their drivers. There is a 'struct udevice' allocated for all devices. However, nothing has been activated (except for the root device). Each bound device that was created -from a U_BOOT_DEVICE() declaration will hold the platdata pointer specified +from a U_BOOT_DRVINFO() declaration will hold the plat pointer specified in that declaration. For a bound device created from the device tree, -platdata will be NULL, but of_offset will be the offset of the device tree +plat will be NULL, but of_offset will be the offset of the device tree node that caused the device to be created. The uclass is set correctly for the device. +The device's sequence number is assigned, either the requested one or the next +available one (after all aliases are processed) if nothing particular is +requested. + The device's bind() method is permitted to perform simple actions, but should not scan the device tree node, not initialise hardware, nor set up structures or allocate memory. All of these tasks should be left for @@ -690,52 +712,52 @@ Most devices have data in the device tree which they can read to find out the base address of hardware registers and parameters relating to driver operation. This is called 'ofdata' (Open-Firmware data). -The device's_ofdata_to_platdata() implemnents allocation and reading of -platdata. A parent's ofdata is always read before a child. +The device's of_to_plat() implemnents allocation and reading of +plat. A parent's ofdata is always read before a child. The steps are: - 1. If priv_auto_alloc_size is non-zero, then the device-private space + 1. If priv_auto is non-zero, then the device-private space is allocated for the device and zeroed. It will be accessible as dev->priv. The driver can put anything it likes in there, but should use it for run-time information, not platform data (which should be static and known before the device is probed). - 2. If platdata_auto_alloc_size is non-zero, then the platform data space + 2. If plat_auto is non-zero, then the platform data space is allocated. This is only useful for device tree operation, since otherwise you would have to specific the platform data in the - U_BOOT_DEVICE() declaration. The space is allocated for the device and - zeroed. It will be accessible as dev->platdata. + U_BOOT_DRVINFO() declaration. The space is allocated for the device and + zeroed. It will be accessible as dev->plat. - 3. If the device's uclass specifies a non-zero per_device_auto_alloc_size, + 3. If the device's uclass specifies a non-zero per_device_auto, then this space is allocated and zeroed also. It is allocated for and stored in the device, but it is uclass data. owned by the uclass driver. It is possible for the device to access it. - 4. If the device's immediate parent specifies a per_child_auto_alloc_size + 4. If the device's immediate parent specifies a per_child_auto then this space is allocated. This is intended for use by the parent device to keep track of things related to the child. For example a USB flash stick attached to a USB host controller would likely use this space. The controller can hold information about the USB state of each of its children. - 5. If the driver provides an ofdata_to_platdata() method, then this is + 5. If the driver provides an of_to_plat() method, then this is called to convert the device tree data into platform data. This should do various calls like dev_read_u32(dev, ...) to access the node and store - the resulting information into dev->platdata. After this point, the device + the resulting information into dev->plat. After this point, the device works the same way whether it was bound using a device tree node or - U_BOOT_DEVICE() structure. In either case, the platform data is now stored - in the platdata structure. Typically you will use the - platdata_auto_alloc_size feature to specify the size of the platform data + U_BOOT_DRVINFO() structure. In either case, the platform data is now stored + in the plat structure. Typically you will use the + plat_auto feature to specify the size of the platform data structure, and U-Boot will automatically allocate and zero it for you before - entry to ofdata_to_platdata(). But if not, you can allocate it yourself in - ofdata_to_platdata(). Note that it is preferable to do all the device tree - decoding in ofdata_to_platdata() rather than in probe(). (Apart from the + entry to of_to_plat(). But if not, you can allocate it yourself in + of_to_plat(). Note that it is preferable to do all the device tree + decoding in of_to_plat() rather than in probe(). (Apart from the ugliness of mixing configuration and run-time data, one day it is possible that U-Boot will cache platform data for devices which are regularly de/activated). - 5. The device is marked 'platdata valid'. + 6. The device is marked 'plat valid'. Note that ofdata reading is always done (for a child and all its parents) before probing starts. Thus devices go through two distinct states when @@ -744,7 +766,7 @@ the device up. Having probing separate from ofdata-reading helps deal with of-platdata, where the probe() method is common to both DT/of-platdata operation, but the -ofdata_to_platdata() method is implemented differently. +of_to_plat() method is implemented differently. Another case has come up where this separate is useful. Generation of ACPI tables uses the of-platdata but does not want to probe the device. Probing @@ -755,18 +777,18 @@ even be possible to probe the device - e.g. an SD card which is not present will cause an error on probe, yet we still must tell Linux about the SD card connector in case it is used while Linux is running. -It is important that the ofdata_to_platdata() method does not actually probe +It is important that the of_to_plat() method does not actually probe the device itself. However there are cases where other devices must be probed -in the ofdata_to_platdata() method. An example is where a device requires a +in the of_to_plat() method. An example is where a device requires a GPIO for it to operate. To select a GPIO obviously requires that the GPIO device is probed. This is OK when used by common, core devices such as GPIO, clock, interrupts, reset and the like. If your device relies on its parent setting up a suitable address space, so that dev_read_addr() works correctly, then make sure that the parent device -has its setup code in ofdata_to_platdata(). If it has it in the probe method, +has its setup code in of_to_plat(). If it has it in the probe method, then you cannot call dev_read_addr() from the child device's -ofdata_to_platdata() method. Move it to probe() instead. Buses like PCI can +of_to_plat() method. Move it to probe() instead. Buses like PCI can fall afoul of this rule. Activation/probe @@ -780,28 +802,24 @@ as above and then following these steps (see device_probe()): This means (for example) that an I2C driver will require that its bus be activated. - 2. The device's sequence number is assigned, either the requested one - (assuming no conflicts) or the next available one if there is a conflict - or nothing particular is requested. - - 4. The device's probe() method is called. This should do anything that + 2. The device's probe() method is called. This should do anything that is required by the device to get it going. This could include checking that the hardware is actually present, setting up clocks for the hardware and setting up hardware registers to initial values. The code in probe() can access: - - platform data in dev->platdata (for configuration) + - platform data in dev->plat (for configuration) - private data in dev->priv (for run-time state) - uclass data in dev->uclass_priv (for things the uclass stores about this device) - Note: If you don't use priv_auto_alloc_size then you will need to + Note: If you don't use priv_auto then you will need to allocate the priv space here yourself. The same applies also to - platdata_auto_alloc_size. Remember to free them in the remove() method. + plat_auto. Remember to free them in the remove() method. - 5. The device is marked 'activated' + 3. The device is marked 'activated' - 10. The uclass's post_probe() method is called, if one exists. This may + 4. The uclass's post_probe() method is called, if one exists. This may cause the uclass to do some housekeeping to record the device as activated and 'known' by the uclass. @@ -837,27 +855,20 @@ remove it. This performs the probe steps in reverse: 4. The device memory is freed (platform data, private data, uclass data, parent data). - Note: Because the platform data for a U_BOOT_DEVICE() is defined with a + Note: Because the platform data for a U_BOOT_DRVINFO() is defined with a static pointer, it is not de-allocated during the remove() method. For a device instantiated using the device tree data, the platform data will be dynamically allocated, and thus needs to be deallocated during the remove() method, either: - - if the platdata_auto_alloc_size is non-zero, the deallocation + - if the plat_auto is non-zero, the deallocation happens automatically within the driver model core; or - - when platdata_auto_alloc_size is 0, both the allocation (in probe() - or preferably ofdata_to_platdata()) and the deallocation in remove() + - when plat_auto is 0, both the allocation (in probe() + or preferably of_to_plat()) and the deallocation in remove() are the responsibility of the driver author. - 5. The device sequence number is set to -1, meaning that it no longer - has an allocated sequence. If the device is later reactivated and that - sequence number is still free, it may well receive the name sequence - number again. But from this point, the sequence number previously used - by this device will no longer exist (think of SPI bus 2 being removed - and bus 2 is no longer available for use). - - 6. The device is marked inactive. Note that it is still bound, so the + 5. The device is marked inactive. Note that it is still bound, so the device structure itself is not freed at this point. Should the device be activated again, then the cycle starts again at step 2 above. @@ -890,14 +901,14 @@ original patches, but makes at least the following changes: the driver operations structure in the driver, rather than passing it to the driver bind function. - Rename some structures to make them more similar to Linux (struct udevice - instead of struct instance, struct platdata, etc.) + instead of struct instance, struct plat, etc.) - Change the name 'core' to 'uclass', meaning U-Boot class. It seems that this concept relates to a class of drivers (or a subsystem). We shouldn't use 'class' since it is a C++ reserved word, so U-Boot class (uclass) seems better than 'core'. - Remove 'struct driver_instance' and just use a single 'struct udevice'. This removes a level of indirection that doesn't seem necessary. -- Built in device tree support, to avoid the need for platdata +- Built in device tree support, to avoid the need for plat - Removed the concept of driver relocation, and just make it possible for the new driver (created after relocation) to access the old driver data. I feel that relocation is a very special case and will only apply to a few @@ -920,7 +931,7 @@ property can provide better control granularity on which device is bound before relocation. While with DM_FLAG_PRE_RELOC flag of the driver all devices with the same driver are bound, which requires allocation a large amount of memory. When device tree is not used, DM_FLAG_PRE_RELOC is the -only way for statically declared devices via U_BOOT_DEVICE() to be bound +only way for statically declared devices via U_BOOT_DRVINFO() to be bound prior to relocation. It is possible to limit this to specific relocation steps, by using |