[PATCH] pxa2xx/cpufreq: Fix DRI computation

[marek.vasut@gmail.com (Marek Vasut)]

Dne ?t 8. ?ervna 2010 13:23:06 Robert Jarzmik napsal(a):
> Marek Vasut <marek.vasut@gmail.com> writes:
> > The DRI field was incorrectly computed, causing various hangs and weird
> > behaviour on PXA2xx machines. This patch introduces the DRI computation
> > according to the PXA255 (January 2004) and PXA270 (MV-S301039-00 Rev. A)
> > datasheets.
> > 
> > NOTE: The CPU type is checked only once, so the code is a little bit
> > faster now.
> > 
> > Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
> > ---
> > 
> >  arch/arm/mach-pxa/cpufreq-pxa2xx.c |   33
> >  +++++++++++++++++++++++++++++---- 1 files changed, 29 insertions(+), 4
> >  deletions(-)
> > 
> > diff --git a/arch/arm/mach-pxa/cpufreq-pxa2xx.c
> > b/arch/arm/mach-pxa/cpufreq-pxa2xx.c index 9e4d981..5373db0 100644
> > --- a/arch/arm/mach-pxa/cpufreq-pxa2xx.c
> > +++ b/arch/arm/mach-pxa/cpufreq-pxa2xx.c
> > @@ -251,17 +251,42 @@ static void init_sdram_rows(void)
> > 
> >  	if (mdcnfg & (MDCNFG_DE0 | MDCNFG_DE1))
> >  	
> >  		drac0 = MDCNFG_DRAC0(mdcnfg);
> > 
> > -	sdram_rows = 1 << (11 + max(drac0, drac2));
> > +	sdram_rows = 11 + max(drac0, drac2);
> 
> I don't think that's correct.
> From DRACn, you learn that SDRAM row is selected from 11+DRACn bits. That
> means that if drac == 2, then the SDRAM row is a number between 0 and
> (11+drac0) - 1. That in turn means that the number of SDRAM rows is : 2 ^
> (11 + drac0). Example:
>  - drac0 = 2 : row encoded on 13 bits => 2^13 rows (ie. 1 << (11 + 2)).

That I'm aware of, but are you sure the TRM means it that way ?
> 
> >  static u32 mdrefr_dri(unsigned int freq)
> >  {
> >  
> >  	u32 dri = 0;
> > 
> > -	if (cpu_is_pxa25x())
> > -		dri = ((freq * SDRAM_TREF) / (sdram_rows * 32));
> > +	/*
> > +	 * PXA255 (6.5.3):
> > +	 * 	DRI = (Refresh time / rows * memory clock frequency) / 32
> > +	 * PXA270 (Table 91):
> > +	 * 	DRI = (Refresh time / rows * memory clock frequency - 31) / 32
> > +	 *
> > +	 * Memory clock frequency is in MHz here! (Refresh time is in ms).
> > +	 */
> 
> I don't agree here either. The "freq" variable is in kHz.

That's concerning the TRM, not the freq value. In TRM, it's in MHz.

> It comes from
> "new_freq_mem = pxa_freq_settings[idx].membus;" in pxa_set_target(). The
> membus value is in kHz, as in tables pxaXXX_freqs (see 104000 and 208000,
> second column in pxa27x_freqs for example). As refresh time is in ms,
> there is no need for a 1000th multiplier.
> 
> And my understanding is that the legacy formula is incorrect, as you
> discovered it. Yet it should be, IMO :
>     if (cpu_is_pxa27x())
> -       dri = ((freq * SDRAM_TREF) / (sdram_rows - 31)) / 32;
> +       dri = ((freq * SDRAM_TREF) / sdram_rows - 31) / 32;
> 
> This is the only change to apply IMHO.

Ok, but still, even though I fixed it your way, it doesn't fix the real problem, 
I'll recheck though, I just need a few days too.

Cheers
> 
> Can you confirm my analysis ?