[PATCH 2/2] OMAP3: PM: Do not rely on ROM code to restore CM_AUTOIDLE_PLL.AUTO_PERIPH_DPLL

[Eduardo Valentin]

Hello Sanjeev,

On Thu, Apr 14, 2011 at 12:36:17PM -0500, Premi, Sanjeev wrote:
> > -----Original Message-----
> > From: Valentin, Eduardo 
> > Sent: Thursday, April 14, 2011 11:04 PM
> > To: Premi, Sanjeev
> > Cc: Valentin, Eduardo; Paul Walmsley; Kevin Hilman; 
> > Linux-OMAP; Linux-ARM
> > Subject: Re: [PATCH 2/2] OMAP3: PM: Do not rely on ROM code 
> > to restore CM_AUTOIDLE_PLL.AUTO_PERIPH_DPLL
> > 
> > Hello Sanjeev,
> > 
> > 
> > On Thu, Apr 14, 2011 at 09:13:14AM -0500, Premi, Sanjeev wrote:
> > > > -----Original Message-----
> > > > From: linux-omap-owner at vger.kernel.org 
> > > > [mailto:linux-omap-owner at vger.kernel.org] On Behalf Of 
> > > > Valentin, Eduardo
> > > > Sent: Wednesday, April 13, 2011 8:51 PM
> > > > To: Paul Walmsley; Kevin Hilman
> > > > Cc: Linux-OMAP; Linux-ARM; Valentin, Eduardo
> > > > Subject: [PATCH 2/2] OMAP3: PM: Do not rely on ROM code to 
> > > > restore CM_AUTOIDLE_PLL.AUTO_PERIPH_DPLL
> > > > 
> > > > As per OMAP3 erratum (i671), ROM code adds extra latencies while
> > > > restoring CM_AUTOIDLE_PLL register, if AUTO_PERIPH_DPLL 
> > is equal to 1.
> > > > 
> > > > This patch stores 0's in scratchpad content area corresponding to
> > > > AUTO_PERIPH_DPLL, to prevent ROM code to try to lock per 
> > DPLL, since
> > > > it won't respect proper programing scheme.
> > > > 
> > > > This register is then stored in prcm context. The saving 
> > and restore
> > > > is now done by kernel side.
> > > > 
> > > > Here follow the erratum description
> > > > 
> > > > DESCRIPTION
> > > > 
> > > > After OFF mode transition, among many restorations, the ROM 
> > > > Code restores the
> > > > CM_AUTOIDLE_PLL register, and after that, it tries to relock 
> > > > the PER DPLL.
> > > > 
> > > > In case the restoration data stored in scratchpad memory 
> > > > contains a field
> > > > CM_AUTOIDLE_PLL.AUTO_PERIPH_DPLL = 1, then the way the ROM 
> > > > Code restores and
> > > > locks the PER DPLL does not respect the PER DPLL 
> > programming scheme.
> > > > 
> > > > In that case, the DPLL might not lock. Meanwhile, when trying 
> > > > to lock the PER
> > > > DPLL, the ROM Code does not hang. Only extra latencies are 
> > > > introduced at
> > > > wake-up.
> > > > 
> > > 
> > > [sp] You seem to have missed this patch:
> > > http://marc.info/?l=linux-arm-kernel&m=129735383925285&w=2
> > 
> > Right,
> > 
> > But that one doesn't clear the AUTO_PERIPH_DPLL bits in the 
> > scratchpad area
> > to avoid rom code extra overhead (check my patch description).
> > 
> > Besides, why do we want to add more code inside omap_sram_idle,
> > if we have better places to this S&R?
> 
> Didn't see that as a comment earlier?

Better later than never :-) ?

> 
> ~sanjeev
> 
> > 
> > 
> > > 
> > > ~sanjeev
> > > 
> > > 
> > 
> > All best,
> > 
> > --
> > Eduardo Valentin
> > 


Cheers,

-- 
Eduardo Valentin