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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> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Tested-by: Bin Meng <bmeng.cn@gmail.com> [bmeng: fix 2 issues in the doc and include the doc in the index.rst] Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
62 lines
2.6 KiB
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62 lines
2.6 KiB
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.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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Debugging driver model
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======================
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This document aims to provide help when you cannot work out why driver model is
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not doing what you expect.
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Useful techniques in general
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----------------------------
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Here are some useful debugging features generally.
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- If you are writing a new feature, consider doing it in sandbox instead of
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on your board. Sandbox has no limits, allows easy debugging (e.g. gdb) and
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you can write emulators for most common devices.
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- Put '#define DEBUG' at the top of a file, to activate all the debug() and
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log_debug() statements in that file.
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- Where logging is used, change the logging level, e.g. in SPL with
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CONFIG_SPL_LOG_MAX_LEVEL=7 (which is LOGL_DEBUG) and
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CONFIG_LOG_DEFAULT_LEVEL=7
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- Where logging of return values is implemented with log_msg_ret(), set
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CONFIG_LOG_ERROR_RETURN=y to see exactly where the error is happening
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- Make sure you have a debug UART enabled - see CONFIG_DEBUG_UART. With this
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you can get serial output (printf(), etc.) before the serial driver is
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running.
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- Use a JTAG emulator to set breakpoints and single-step through code
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Not that most of these increase code/data size somewhat when enabled.
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Failure to locate a device
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--------------------------
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Let's say you have uclass_first_device_err() and it is not finding anything.
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If it is returning an error, then that gives you a clue. Look up linux/errno.h
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to see errors. Common ones are:
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- -ENOMEM which indicates that memory is short. If it happens in SPL or
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before relocation in U-Boot, check CONFIG_SPL_SYS_MALLOC_F_LEN and
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CONFIG_SYS_MALLOC_F_LEN as they may need to be larger. Add '#define DEBUG'
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at the very top of malloc_simple.c to get an idea of where your memory is
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going.
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- -EINVAL which typically indicates that something was missing or wrong in
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the device tree node. Check that everything is correct and look at the
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ofdata_to_platdata() method in the driver.
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If there is no error, you should check if the device is actually bound. Call
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dm_dump_all() just before you locate the device to make sure it exists.
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If it does not exist, check your device tree compatible strings match up with
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what the driver expects (in the struct udevice_id array).
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If you are using of-platdata (e.g. CONFIG_SPL_OF_PLATDATA), check that the
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driver name is the same as the first compatible string in the device tree (with
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invalid-variable characters converted to underscore).
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If you are really stuck, #define DEBUG at the top of lists.c should show you
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what is going on.
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