On Wed, Sep 25, 2019 at 10:58 PM Simon Glass sjg@chromium.org wrote:
Sometimes devices don't appear and it can be confusing. Add a few notes to help with this situation.
Signed-off-by: Simon Glass sjg@chromium.org
doc/driver-model/debugging.rst | 62 ++++++++++++++++++++++++++++++++++
missed updating index.rst to include this doc.
I can fix this when applying.
1 file changed, 62 insertions(+) create mode 100644 doc/driver-model/debugging.rst
diff --git a/doc/driver-model/debugging.rst b/doc/driver-model/debugging.rst new file mode 100644 index 00000000000..9711dd6d653 --- /dev/null +++ b/doc/driver-model/debugging.rst @@ -0,0 +1,62 @@ +.. SPDX-License-Identifier: GPL-2.0+ +.. sectionauthor:: Simon Glass sjg@chromium.org
+Debugging driver model +======================
+This document aims to provide help when you cannot work out why driver model is +not doing what you expect.
+Useful techniques in general +----------------------------
+Here are some useful debugging features generally.
- If you are writing a new feature, consider doing it in sandbox instead of
on your board. Sandbox has no limits, allows each debugging (e.g. gdb) and
easy debugging
you can writing emulators for most common devices.
write
- Put '#define DEBUG' at the top of a file, to activate all the debug() and
log_debug() statements in that file.
- Where logging is used, change the logging level, e.g. in SPL with
CONFIG_SPL_LOG_MAX_LEVEL=7 (which is LOGL_DEBUG) andCONFIG_LOG_DEFAULT_LEVEL=7
- Where logging of return values is implemented with log_msg_ret(), set
CONFIG_LOG_ERROR_RETURN=y to see exactly where the error is happening
- Make sure you have a debug UART enabled - see CONFIG_DEBUG_UART. With this
you can get serial output (printf(), etc.) before the serial driver isrunning.
- Use a JTAG emulator to set breakpoints and single-step through code
+Not that most of these increase code/data size somewhat when enabled.
+Failure to locate a device +--------------------------
+Let's say you have uclass_first_device_err() and it is not finding anything.
+If it is returning an error, then that gives you a clue. Look up linux/errno.h +to see errors. Common ones are:
- -ENOMEM which indicates that memory is short. If it happens in SPL or
before relocation in U-Boot, check CONFIG_SPL_SYS_MALLOC_F_LEN andCONFIG_SYS_MALLOC_F_LEN as they may need to be larger. Add '#define DEBUG'at the very top of malloc_simple.c to get an idea of where your memory isgoing.
- -EINVAL which typically indicates that something was missing or wrong in
the device tree node. Check that everything is correct and look at theofdata_to_platdata() method in the driver.+If there is no error, you should check if the device is actually bound. Call +dm_dump_all() just before you locate the device to make sure it exists.
+If it does not exist, check your device tree compatible strings match up with +what the driver expects (in the struct udevice_id array).
+If you are using of-platdata (e.g. CONFIG_SPL_OF_PLATDATA), check that the +driver name is the same as the first compatible string in the device tree (with +invalid-variable characters converted to underscore).
+If you are really stuck, #define DEBUG at the top of lists.c should show you
+what is going on.
Other than that,
Reviewed-by: Bin Meng bmeng.cn@gmail.com Tested-by: Bin Meng bmeng.cn@gmail.com