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Simon Glass39782af2016-07-04 11:58:07 -06001Driver Model Compiled-in Device Tree / Platform Data
2====================================================
3
4
5Introduction
6------------
7
8Device tree is the standard configuration method in U-Boot. It is used to
9define what devices are in the system and provide configuration information
10to these devices.
11
12The overhead of adding device tree access to U-Boot is fairly modest,
13approximately 3KB on Thumb 2 (plus the size of the DT itself). This means
14that in most cases it is best to use device tree for configuration.
15
16However there are some very constrained environments where U-Boot needs to
17work. These include SPL with severe memory limitations. For example, some
18SoCs require a 16KB SPL image which must include a full MMC stack. In this
19case the overhead of device tree access may be too great.
20
21It is possible to create platform data manually by defining C structures
Simon Glass12696252016-07-04 11:58:42 -060022for it, and reference that data in a U_BOOT_DEVICE() declaration. This
23bypasses the use of device tree completely, effectively creating a parallel
24configuration mechanism. But it is an available option for SPL.
Simon Glass39782af2016-07-04 11:58:07 -060025
Simon Glass12696252016-07-04 11:58:42 -060026As an alternative, a new 'of-platdata' feature is provided. This converts the
Simon Glass39782af2016-07-04 11:58:07 -060027device tree contents into C code which can be compiled into the SPL binary.
28This saves the 3KB of code overhead and perhaps a few hundred more bytes due
29to more efficient storage of the data.
30
Simon Glass12696252016-07-04 11:58:42 -060031Note: Quite a bit of thought has gone into the design of this feature.
32However it still has many rough edges and comments and suggestions are
33strongly encouraged! Quite possibly there is a much better approach.
34
Simon Glass39782af2016-07-04 11:58:07 -060035
36Caveats
37-------
38
39There are many problems with this features. It should only be used when
Simon Glass12696252016-07-04 11:58:42 -060040strictly necessary. Notable problems include:
Simon Glass39782af2016-07-04 11:58:07 -060041
Simon Glass12696252016-07-04 11:58:42 -060042 - Device tree does not describe data types. But the C code must define a
43 type for each property. These are guessed using heuristics which
Simon Glass39782af2016-07-04 11:58:07 -060044 are wrong in several fairly common cases. For example an 8-byte value
45 is considered to be a 2-item integer array, and is byte-swapped. A
46 boolean value that is not present means 'false', but cannot be
47 included in the structures since there is generally no mention of it
48 in the device tree file.
49
50 - Naming of nodes and properties is automatic. This means that they follow
51 the naming in the device tree, which may result in C identifiers that
Simon Glass12696252016-07-04 11:58:42 -060052 look a bit strange.
Simon Glass39782af2016-07-04 11:58:07 -060053
54 - It is not possible to find a value given a property name. Code must use
55 the associated C member variable directly in the code. This makes
56 the code less robust in the face of device-tree changes. It also
57 makes it very unlikely that your driver code will be useful for more
58 than one SoC. Even if the code is common, each SoC will end up with
Simon Glass12696252016-07-04 11:58:42 -060059 a different C struct name, and a likely a different format for the
60 platform data.
Simon Glass39782af2016-07-04 11:58:07 -060061
62 - The platform data is provided to drivers as a C structure. The driver
63 must use the same structure to access the data. Since a driver
64 normally also supports device tree it must use #ifdef to separate
65 out this code, since the structures are only available in SPL.
66
67
68How it works
69------------
70
71The feature is enabled by CONFIG SPL_OF_PLATDATA. This is only available
72in SPL and should be tested with:
73
74 #if CONFIG_IS_ENABLED(SPL_OF_PLATDATA)
75
76A new tool called 'dtoc' converts a device tree file either into a set of
77struct declarations, one for each compatible node, or a set of
78U_BOOT_DEVICE() declarations along with the actual platform data for each
79device. As an example, consider this MMC node:
80
81 sdmmc: dwmmc@ff0c0000 {
82 compatible = "rockchip,rk3288-dw-mshc";
83 clock-freq-min-max = <400000 150000000>;
84 clocks = <&cru HCLK_SDMMC>, <&cru SCLK_SDMMC>,
85 <&cru SCLK_SDMMC_DRV>, <&cru SCLK_SDMMC_SAMPLE>;
86 clock-names = "biu", "ciu", "ciu_drv", "ciu_sample";
87 fifo-depth = <0x100>;
88 interrupts = <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>;
89 reg = <0xff0c0000 0x4000>;
90 bus-width = <4>;
91 cap-mmc-highspeed;
92 cap-sd-highspeed;
93 card-detect-delay = <200>;
94 disable-wp;
95 num-slots = <1>;
96 pinctrl-names = "default";
97 pinctrl-0 = <&sdmmc_clk>, <&sdmmc_cmd>, <&sdmmc_cd>, <&sdmmc_bus4>;
98 vmmc-supply = <&vcc_sd>;
99 status = "okay";
100 u-boot,dm-pre-reloc;
101 };
102
103
104Some of these properties are dropped by U-Boot under control of the
105CONFIG_OF_SPL_REMOVE_PROPS option. The rest are processed. This will produce
106the following C struct declaration:
107
108struct dtd_rockchip_rk3288_dw_mshc {
109 fdt32_t bus_width;
110 bool cap_mmc_highspeed;
111 bool cap_sd_highspeed;
112 fdt32_t card_detect_delay;
113 fdt32_t clock_freq_min_max[2];
114 struct phandle_2_cell clocks[4];
115 bool disable_wp;
116 fdt32_t fifo_depth;
117 fdt32_t interrupts[3];
118 fdt32_t num_slots;
119 fdt32_t reg[2];
Simon Glass39782af2016-07-04 11:58:07 -0600120 fdt32_t vmmc_supply;
121};
122
123and the following device declaration:
124
125static struct dtd_rockchip_rk3288_dw_mshc dtv_dwmmc_at_ff0c0000 = {
126 .fifo_depth = 0x100,
127 .cap_sd_highspeed = true,
128 .interrupts = {0x0, 0x20, 0x4},
129 .clock_freq_min_max = {0x61a80, 0x8f0d180},
130 .vmmc_supply = 0xb,
131 .num_slots = 0x1,
Simon Glass12696252016-07-04 11:58:42 -0600132 .clocks = {{&dtv_clock_controller_at_ff760000, 456},
133 {&dtv_clock_controller_at_ff760000, 68},
134 {&dtv_clock_controller_at_ff760000, 114},
135 {&dtv_clock_controller_at_ff760000, 118}},
Simon Glass39782af2016-07-04 11:58:07 -0600136 .cap_mmc_highspeed = true,
137 .disable_wp = true,
138 .bus_width = 0x4,
139 .u_boot_dm_pre_reloc = true,
140 .reg = {0xff0c0000, 0x4000},
141 .card_detect_delay = 0xc8,
142};
143U_BOOT_DEVICE(dwmmc_at_ff0c0000) = {
144 .name = "rockchip_rk3288_dw_mshc",
145 .platdata = &dtv_dwmmc_at_ff0c0000,
Simon Glass12696252016-07-04 11:58:42 -0600146 .platdata_size = sizeof(dtv_dwmmc_at_ff0c0000),
Simon Glass39782af2016-07-04 11:58:07 -0600147};
148
149The device is then instantiated at run-time and the platform data can be
150accessed using:
151
152 struct udevice *dev;
153 struct dtd_rockchip_rk3288_dw_mshc *plat = dev_get_platdata(dev);
154
155This avoids the code overhead of converting the device tree data to
156platform data in the driver. The ofdata_to_platdata() method should
157therefore do nothing in such a driver.
158
159
Simon Glass12696252016-07-04 11:58:42 -0600160Converting of-platdata to a useful form
161---------------------------------------
162
163Of course it would be possible use the of-platdata directly in your driver
164whenever configuration information is required. However this meands that the
165driver will not be able to support device tree, since the of-platdata
166structure is not available when device tree is used. It would make no sense
167to use this structure if device tree were available, since the structure has
168all the limitations metioned in caveats above.
169
170Therefore it is recommended that the of-platdata structure should be used
171only in the probe() method of your driver. It cannot be used in the
172ofdata_to_platdata() method since this is not called when platform data is
173already present.
174
175
Simon Glass39782af2016-07-04 11:58:07 -0600176How to structure your driver
177----------------------------
178
179Drivers should always support device tree as an option. The of-platdata
180feature is intended as a add-on to existing drivers.
181
Simon Glass12696252016-07-04 11:58:42 -0600182Your driver should convert the platdata struct in its probe() method. The
183existing device tree decoding logic should be kept in the
184ofdata_to_platdata() method and wrapped with #if.
Simon Glass39782af2016-07-04 11:58:07 -0600185
186For example:
187
188 #include <dt-structs.h>
189
190 struct mmc_platdata {
191 #if CONFIG_IS_ENABLED(SPL_OF_PLATDATA)
Simon Glass12696252016-07-04 11:58:42 -0600192 /* Put this first since driver model will copy the data here */
Simon Glass39782af2016-07-04 11:58:07 -0600193 struct dtd_mmc dtplat;
194 #endif
195 /*
196 * Other fields can go here, to be filled in by decoding from
Simon Glass12696252016-07-04 11:58:42 -0600197 * the device tree (or the C structures when of-platdata is used).
Simon Glass39782af2016-07-04 11:58:07 -0600198 */
199 int fifo_depth;
200 };
201
202 static int mmc_ofdata_to_platdata(struct udevice *dev)
203 {
204 #if !CONFIG_IS_ENABLED(SPL_OF_PLATDATA)
Simon Glass12696252016-07-04 11:58:42 -0600205 /* Decode the device tree data */
Simon Glass39782af2016-07-04 11:58:07 -0600206 struct mmc_platdata *plat = dev_get_platdata(dev);
207 const void *blob = gd->fdt_blob;
208 int node = dev->of_offset;
209
210 plat->fifo_depth = fdtdec_get_int(blob, node, "fifo-depth", 0);
211 #endif
212
213 return 0;
214 }
215
216 static int mmc_probe(struct udevice *dev)
217 {
218 struct mmc_platdata *plat = dev_get_platdata(dev);
Simon Glass12696252016-07-04 11:58:42 -0600219
Simon Glass39782af2016-07-04 11:58:07 -0600220 #if CONFIG_IS_ENABLED(SPL_OF_PLATDATA)
Simon Glass12696252016-07-04 11:58:42 -0600221 /* Decode the of-platdata from the C structures */
Simon Glass39782af2016-07-04 11:58:07 -0600222 struct dtd_mmc *dtplat = &plat->dtplat;
223
Simon Glass12696252016-07-04 11:58:42 -0600224 plat->fifo_depth = dtplat->fifo_depth;
225 #endif
Simon Glass39782af2016-07-04 11:58:07 -0600226 /* Set up the device from the plat data */
227 writel(plat->fifo_depth, ...)
Simon Glass39782af2016-07-04 11:58:07 -0600228 }
229
230 static const struct udevice_id mmc_ids[] = {
231 { .compatible = "vendor,mmc" },
232 { }
233 };
234
235 U_BOOT_DRIVER(mmc_drv) = {
236 .name = "mmc",
237 .id = UCLASS_MMC,
238 .of_match = mmc_ids,
239 .ofdata_to_platdata = mmc_ofdata_to_platdata,
240 .probe = mmc_probe,
241 .priv_auto_alloc_size = sizeof(struct mmc_priv),
242 .platdata_auto_alloc_size = sizeof(struct mmc_platdata),
243 };
244
245
246In the case where SPL_OF_PLATDATA is enabled, platdata_auto_alloc_size is
Simon Glass12696252016-07-04 11:58:42 -0600247still used to allocate space for the platform data. This is different from
248the normal behaviour and is triggered by the use of of-platdata (strictly
249speaking it is a non-zero platdata_size which triggers this).
Simon Glass39782af2016-07-04 11:58:07 -0600250
Simon Glass12696252016-07-04 11:58:42 -0600251The of-platdata struct contents is copied from the C structure data to the
252start of the newly allocated area. In the case where device tree is used,
253the platform data is allocated, and starts zeroed. In this case the
254ofdata_to_platdata() method should still set up the platform data (and the
255of-platdata struct will not be present).
256
257SPL must use either of-platdata or device tree. Drivers cannot use both at
258the same time, but they must support device tree. Supporting of-platdata is
259optional.
260
Simon Glass39782af2016-07-04 11:58:07 -0600261The device tree becomes in accessible when CONFIG_SPL_OF_PLATDATA is enabled,
Simon Glass12696252016-07-04 11:58:42 -0600262since the device-tree access code is not compiled in. A corollary is that
263a board can only move to using of-platdata if all the drivers it uses support
264it. There would be little point in having some drivers require the device
265tree data, since then libfdt would still be needed for those drivers and
266there would be no code-size benefit.
Simon Glass39782af2016-07-04 11:58:07 -0600267
268Internals
269---------
270
271The dt-structs.h file includes the generated file
272(include/generated//dt-structs.h) if CONFIG_SPL_OF_PLATDATA is enabled.
273Otherwise (such as in U-Boot proper) these structs are not available. This
Simon Glass12696252016-07-04 11:58:42 -0600274prevents them being used inadvertently. All usage must be bracketed with
275#if CONFIG_IS_ENABLED(SPL_OF_PLATDATA).
Simon Glass39782af2016-07-04 11:58:07 -0600276
277The dt-platdata.c file contains the device declarations and is is built in
278spl/dt-platdata.c.
279
280Some phandles (thsoe that are recognised as such) are converted into
281points to platform data. This pointer can potentially be used to access the
282referenced device (by searching for the pointer value). This feature is not
283yet implemented, however.
284
285The beginnings of a libfdt Python module are provided. So far this only
286implements a subset of the features.
287
Simon Glass12696252016-07-04 11:58:42 -0600288The 'swig' tool is needed to build the libfdt Python module. If this is not
289found then the Python model is not used and a fallback is used instead, which
290makes use of fdtget.
291
292
293Credits
294-------
295
296This is an implementation of an idea by Tom Rini <trini@konsulko.com>.
Simon Glass39782af2016-07-04 11:58:07 -0600297
298
299Future work
300-----------
Simon Glass39782af2016-07-04 11:58:07 -0600301- Consider programmatically reading binding files instead of device tree
302 contents
Simon Glass39782af2016-07-04 11:58:07 -0600303- Complete the phandle feature
Simon Glass39782af2016-07-04 11:58:07 -0600304- Move to using a full Python libfdt module
305
306--
307Simon Glass <sjg@chromium.org>
Simon Glass12696252016-07-04 11:58:42 -0600308Google, Inc
Simon Glass39782af2016-07-04 11:58:07 -06003096/6/16
Simon Glass12696252016-07-04 11:58:42 -0600310Updated Independence Day 2016