[U-Boot] [PATCH 004/126] dm: core: Add documentation on how to debug driver model

[Bin Meng]

On Wed, Sep 25, 2019 at 10:58 PM Simon Glass <sjg at 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 at 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 at 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) and
> +     CONFIG_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 is
> +     running.
> +   - 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 and
> +     CONFIG_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 is
> +     going.
> +   - -EINVAL which typically indicates that something was missing or wrong in
> +     the device tree node. Check that everything is correct and look at the
> +     ofdata_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 at gmail.com>
Tested-by: Bin Meng <bmeng.cn at gmail.com>