[U-Boot] [PATCH 3/4] dm: do not check dm_root before searching in uclass_root

[Simon Glass]

Hi Masahiro,

On 28 September 2014 09:54, Masahiro YAMADA <yamada.m at jp.panasonic.com> wrote:
> Simon,
>
>
> 2014-09-29 0:17 GMT+09:00 Simon Glass <sjg at chromium.org>:
>> Hi Masahiro,
>>
>> On 28 September 2014 07:52, Masahiro Yamada <yamada.m at jp.panasonic.com> wrote:
>>> The function uclass_find() looks for a uclass in the linked
>>> list of gd->uclass_root; gd->dm_root has nothing to do with
>>> gd->uclass_root.  Remove this confusing code.
>>>
>>> Signed-off-by: Masahiro Yamada <yamada.m at jp.panasonic.com>
>>> ---
>>>
>>>  drivers/core/uclass.c | 2 --
>>>  1 file changed, 2 deletions(-)
>>>
>>> diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
>>> index 901b06e..74df613 100644
>>> --- a/drivers/core/uclass.c
>>> +++ b/drivers/core/uclass.c
>>> @@ -23,8 +23,6 @@ struct uclass *uclass_find(enum uclass_id key)
>>>  {
>>>         struct uclass *uc;
>>>
>>> -       if (!gd->dm_root)
>>> -               return NULL;
>>>         /*
>>>          * TODO(sjg at chromium.org): Optimise this, perhaps moving the found
>>>          * node to the start of the list, or creating a linear array mapping
>>
>> This came in in commit:
>>
>>  c910e2e dm: Avoid accessing uclasses before they are ready
>>
>> Please see that (and the test that was added) for an explanation.
>
>
> Commit c910e2e says:
>
> dm: Avoid accessing uclasses before they are ready
>
> Don't allow access to uclasses before they have been initialised.
>
>
>
> I still don't get it.
> The log did not help me because it is not saying 'why'.
>
> What kind problem would happen if this check was dropped?
>
> gd->dm_root is set when the root device is bound.
> At the first call of uclass_find(), it is true gd->dm_root is NULL,
> but gd->uclass_root is also empty.

But 'empty' means the list is empty. For it to be empty it must be
initialised. But if you call the function before this list init
happens, then it will just crash.

We can use dm_root as an indicator that init has happened.

>
> This function, anyway, returns NULL.
> The behavior is still the same, I think.

You can try this by removing that code and seeing what the test does
(dm_test_uclass_before_ready()).

Regards,
Simon