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of-platdata: improve documentation

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Improve some things in the documentation of OF_PLATDATA that I found
while porting socfgpa_gen5 to it.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Goldschmidt 2019-01-16 20:40:18 +01:00 committed by Simon Glass
parent e5fc79ea71
commit 3600b46117
2 changed files with 22 additions and 15 deletions
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31
doc/driver-model/of-plat.txt
View file

@ -64,17 +64,24 @@ strictly necessary. Notable problems include:
normally also supports device tree it must use #ifdef to separate
out this code, since the structures are only available in SPL.
- Correct relations between nodes are not implemented. This means that
parent/child relations (like bus device iteration) do not work yet.
Some phandles (those that are recognised as such) are converted into
a pointer to platform data. This pointer can potentially be used to
access the referenced device (by searching for the pointer value).
This feature is not yet implemented, however.
How it works
------------
The feature is enabled by CONFIG SPL_OF_PLATDATA. This is only available
in SPL and should be tested with:
The feature is enabled by CONFIG OF_PLATDATA. This is only available in
SPL/TPL and should be tested with:
#if CONFIG_IS_ENABLED(SPL_OF_PLATDATA)
#if CONFIG_IS_ENABLED(OF_PLATDATA)
A new tool called 'dtoc' converts a device tree file either into a set of
struct declarations, one for each compatible node, or a set of
struct declarations, one for each compatible node, and a set of
U_BOOT_DEVICE() declarations along with the actual platform data for each
device. As an example, consider this MMC node:
@ -156,6 +163,13 @@ This avoids the code overhead of converting the device tree data to
platform data in the driver. The ofdata_to_platdata() method should
therefore do nothing in such a driver.
Note that for the platform data to be matched with a driver, the 'name'
property of the U_BOOT_DEVICE() declaration has to match a driver declared
via U_BOOT_DRIVER(). This effectively means that a U_BOOT_DRIVER() with a
'name' corresponding to the devicetree 'compatible' string (after converting
it to a valid name for C) is needed, so a dedicated driver is required for
each 'compatible' string.
Where a node has multiple compatible strings, a #define is used to make them
equivalent, e.g.:
@ -165,8 +179,8 @@ equivalent, e.g.:
Converting of-platdata to a useful form
---------------------------------------
Of course it would be possible use the of-platdata directly in your driver
whenever configuration information is required. However this meands that the
Of course it would be possible to use the of-platdata directly in your driver
whenever configuration information is required. However this means that the
driver will not be able to support device tree, since the of-platdata
structure is not available when device tree is used. It would make no sense
to use this structure if device tree were available, since the structure has
@ -282,11 +296,6 @@ prevents them being used inadvertently. All usage must be bracketed with
The dt-platdata.c file contains the device declarations and is is built in
spl/dt-platdata.c.
Some phandles (thsoe that are recognised as such) are converted into
points to platform data. This pointer can potentially be used to access the
referenced device (by searching for the pointer value). This feature is not
yet implemented, however.
The beginnings of a libfdt Python module are provided. So far this only
implements a subset of the features.

6
dts/Kconfig
View file

@ -265,8 +265,7 @@ config SPL_OF_PLATDATA
This option works by generating C structure declarations for each
compatible string, then adding platform data and U_BOOT_DEVICE
declarations for each node. See README.platdata for more
information.
declarations for each node. See of-plat.txt for more information.
config TPL_OF_PLATDATA
bool "Generate platform data for use in TPL"
@ -287,8 +286,7 @@ config TPL_OF_PLATDATA
This option works by generating C structure declarations for each
compatible string, then adding platform data and U_BOOT_DEVICE
declarations for each node. See README.platdata for more
information.
declarations for each node. See of-plat.txt for more information.
endmenu