Re: [PATCH v2 4/8] ARM: OMAP2+: hwmod: revise hardreset behavior

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Hi Benoît,

On Thu, 19 Apr 2012, Cousson, Benoit wrote:

> The concern of the people doing SW in these embedded processors was mainly
> because we were releasing the reset of processor without loading any SW first
> and thus the processor was executing some random instructions.
> So if we consider a better hwmods definition, we can potentially fix the MMU
> case:
>     'mmu_ipu':
>         'rst_ipu_mmu_cache'
>     'mmu_dsp':
>         'rst_dsp_mmu_cache'
>     'iva_config':
>         'rst_logic'

Wouldn't these still be "pseudo-hwmods?"  Or do each of these actually 
have address space, interconnect ports, etc.?

Another approach that might not require defining pseudo-hwmods is to 
define a per-hard-reset-line flag that could be used to alter the way the 
hwmod code handles the hardreset line.

> But then we do have the processor resets that have to be exposed somewhere.
>     'ipu':
>         'rst_cpu0'
>         'rst_cpu1'
>     'dsp':
>         'rst_dsp'
>     'iva':
>         'rst_seq1'
>         'rst_seq2'
> None of these one should be controlled automatically.

Don't we still want to put these IP blocks into reset until a driver for 
these IP blocks is loaded?

> >   	/*
> > -	 * If an IP contains HW reset lines, then de-assert them in order
> > -	 * to allow the module state transition. Otherwise the PRCM will
> > return
> > -	 * Intransition status, and the init will failed.
> > +	 * If an IP block contains HW reset lines and any of them are
> > +	 * asserted, we let integration code associated with that
> > +	 * block handle the enable.  We've received very little
> > +	 * information on what those driver authors need, and until
> > +	 * detailed information is provided and the driver code is
> > +	 * posted to the public lists, this is probably the best we
> > +	 * can do.
> Maybe we should keep that with some mechanism to prevent it for some IP like
> processors .
> I guess that with that patch, we cannot enable anymore IPU/DSP and IVA at boot
> time.

I am probably misunderstanding your comment, but I don't think there's any 
way at the moment to generically enable those IP blocks without driver 
integration code assistance.

If we leave the hardreset lines asserted in _enable(), then the PRCM 
status for those modules will be stuck in In-transition state, according 
to the previous comments in the code.  I think this will block PM idle 
transitions.  Also we have no way to restore the clockdomain idle settings 
during the second part of the hwmod enable sequence, I think, since it 
will need to be executed by driver integration code :-(

And I don't think we can deassert the hardreset lines in _enable() right 
now, for the reason that you mentioned in your message: unless the driver 
integration code implements a custom reset function, we don't have any way 
to load code into the IP block before deasserting the hardreset.

So at this point I'd propose that we encourage these driver authors to 
implement custom reset functions for their IP blocks that load firmware if 
needed, and put them into idle, similar to what omap3_iva_idle() does in 
mach-omap2/pm34xx.c.  If the custom reset function takes the IP block out 
of hardreset, then the subsequent hwmod enable/idle/shutdown calls should 
work, after this patch.

> Otherwise, it looks fine to me.

Thanks for the review.

- Paul
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