[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 11:04:18AM +0200, Marek Vasut wrote:
> On 05/16/2018 11:00 AM, 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.
> 
> But if this keeps going on, eventually we will regress to where we were
> years ago -- having huge platform specific list of registers to poke to
> set a platform up and that'd be it ?

We should certainly re-evaluate the situation once hwmod finally gets
replaced in the kernel.  That's a long-standing and slowly-but-surely
happening thing.

-- 
Tom
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