[U-Boot] [PATCH v5 4/9] board: ti: dra7xx-evm: turn on USB clocks in late init stage

[Jean-Jacques Hiblot]

On 16/05/2018 00:13, Marek Vasut wrote:
> On 05/15/2018 06:10 PM, Jean-Jacques Hiblot wrote:
>> Hi Marek,
>>
>>
>> On 04/05/2018 21:06, Marek Vasut wrote:
>>>>>>> Shouldnt the driver turn this on?
>>>>>> AFAIK there is no clock driver for the OMAP. So we have to do it
>>>>>> before
>>>>>> the driver is probed.
>>>>> Maybe it's time to implement it instead of piling up those hacks ?
>>>> I was thinking along the same lines at some point but then I realized
>>>> that it will make the SPL really big. And we are already tight on some
>>>> platforms like am335x.
>>> But this is not only SPL , right ? And yes, for SPL you might need to
>>> poke registers or something.
>> IMHO having 2 different ways to enable the clocks in SPL and in u-boot
>> is an not improvement over the current situation.
>> In any case, This is a subject that can be discussed.
> Do you have a better idea ?
I would keep it as it is today.

After studying the clock management in Linux, I believe that 
implementing the clock drivers in u-boot won't be an easy task and 
moreover won't make things much cleaner.
The way clocks are handled in Linux for the omap platforms is not 
completely standard. There are a lot of clocks that are handled by the 
clock framework (pll, mux, some gates, ...) but most of the clock gating 
for peripherals is handled the HWMOD subsystem which automatically 
enables/disables the clocks of the peripherals. Parameters for this 
subsystem are hard-coded in platform code (in 
arch/arm/mach-omap2/omap-hwmod_xxx_data.c) not in the DTS. It also 
handle clock and power domains.
HWMOD is probably going to go away some day, I'm not sure that we want 
to implement it in u-boot. Until hwmod has completely replaced by more 
generic frameworks, I would stick to platform code to enable clocks in 
u-boot.

Jean-Jacques
>
>> Tom, Lokesh,  do you have an opinion on this ?
>>
>> Meanwhile It would nice to have DM_USB support for the DRA7/AM57
>> platforms. It allows using a USB ether adapter with CONFIG_DM_ETHER
>> enabled (default on TI's platform). And this series allows using the USB
>> 3.0 on AM57 evm.
>>
>> JJ
>>
>>
>>
>