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

[Tom Rini]

On Wed, May 16, 2018 at 11:00:54AM +0200, Jean-Jacques Hiblot wrote:
> 
> 
> 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.

Yes, this is an area that doesn't have a small, clean and generic
solution.

-- 
Tom
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