[PATCH 1/2] DM_USB: allow building without OF_CONTROL

[Ivaylo Dimitrov]

On 19.06.21 г. 22:38 ч., Marek Vasut wrote:
> On 6/19/21 9:33 PM, Ivaylo Dimitrov wrote:
>> Hi,
> 
> Hi,
> 
>>>>>>> Currently DM_USB requires OF_CONTROL to be enabled, otherwise 
>>>>>>> link errors
>>>>>>> occur. On the other hand OF_CONTROL requires board code to be 
>>>>>>> migrated to
>>>>>>> DT, which is not always possible or required.
>>>>>>>
>>>>>>> Fix that by conditionally compiling OF_CONTROL specific sections 
>>>>>>> in USB
>>>>>>> related drivers code in the same way like it is done in the other 
>>>>>>> drivers.
>>>>>>> Also, auto select OF_LIBFDT if DM_USB is selected but OF_CONTROL 
>>>>>>> is not.
>>>>>>> Introduce a new Kconfig option OF_NODE used to compile of_node.c 
>>>>>>> in case
>>>>>>> OF_CONTROL is not enabled. Fix deprecation warning condition as 
>>>>>>> well.
>>>>>
>>>>> So, what is the use case of this? Why not just enable DM_USB and 
>>>>> OF_CONTROL ?
>>>>
>>>> OF_CONTROL requires migration to device-tree.
>>>
>>> That's where the supported platforms are heading anyway. Or is there 
>>> some issue with switching the platform you use over to DT ?
>>
>> OK, let me elaborate: It is about enabling DM_USB on N900 (Nokia rx-51 
>> board). For various reasons I am not going to discuss (1), migration 
>> to DM was delayed to the point where we saw "[PATCH] arm: Remove 
>> nokia_rx51 board" with a commit message "This board has not been 
>> converted to CONFIG_DM_USB by the deadline. Remove it." posted. The 
>> missing pieces were WDT (a patch is already merged in -next) and 
>> DM_USB. The board itself does not support host mode, but USB TTY is 
>> very useful for debugging purposes. The particular task I am after is 
>> USB DM migration and the $subject patch allows this to be achieved 
>> with relatively little effort (a couple of defconfig changes), 
>> incomparable with the effort needed for migration to DT. As we are 
>> already past the DM migration deadline I think it makes sense to 
>> fulfil its requirements before undertaking such a big task like 
>> migration to DT.
> 
> This sounds like a workaround though. Can you instead do the full 
> conversion of the board? I am sure the board removal patch can be 
> postponed if there is plan to convert it.

Hard to say if migration to device-tree is even possible on N900 ATM, 
enabling OF_CONTROL increases the size of the produced binary with some 
100k (.dtb not included), making the size of the binary way above our 
budget of ~256k. Sure, board config does not enable -mthumb, but omap3 
in rx-51 suffers from ARM errata 430973 and noone can guarantee we're 
not going to see SIGILL faults if we enable it. Which it seems we are 
forced to do even with DM_USB migration only.

Re workaround - I took examples of #ifdef's from the current u-boot code 
(mmc, i2c, etc.) so workaround or not, it is no different to what the 
other drivers are doing.

I don't really understand where this requirement to convert to DTS comes 
from - will boards that are not converted be removed at some point? When 
is that deadline if exists? If there is no such deadline, why shall we 
spend who knows how many hours just because "you know, it sounds like a 
good idea to convert to DTS"? You understand this is not a trivial task 
and given the pace rx-51 patches were reviewed lately, it will easily 
take 2 years to do that conversion.

To sum it up - maybe I can do a full DTS migration, but I don't see a 
point in doing it ATM. The $subject patch allows rx-51 to be fully 
migrated to DM and does nothing different to what already is done all 
over the place.

Regards,
Ivo