[PATCH 3/7] ARM: tegra30: cpuidle: add LP2 driver for secondary CPUs

[Joseph Lo]

On Tue, 2012-10-09 at 16:38 +0800, Lorenzo Pieralisi wrote:
> On Tue, Oct 09, 2012 at 05:13:15AM +0100, Joseph Lo wrote:
> 
> [...]
> 
> > > > +ENTRY(tegra_flush_l1_cache)
> > > > +       stmfd   sp!, {r4-r5, r7, r9-r11, lr}
> > > > +       dmb                                     @ ensure ordering
> > > > +
> > > > +       /* Disable the data cache */
> > > > +       mrc     p15, 0, r2, c1, c0, 0
> > > > +       bic     r2, r2, #CR_C
> > > > +       dsb
> > > > +       mcr     p15, 0, r2, c1, c0, 0
> > > > +
> > > > +       /* Flush data cache */
> > > > +       mov     r10, #0
> > > > +#ifdef CONFIG_PREEMPT
> > > > +       save_and_disable_irqs_notrace r9        @ make cssr&csidr read atomic
> > > > +#endif
> > > > +       mcr     p15, 2, r10, c0, c0, 0          @ select current cache level in cssr
> > > > +       isb                                     @ isb to sych the new cssr&csidr
> > > > +       mrc     p15, 1, r1, c0, c0, 0           @ read the new csidr
> > > > +#ifdef CONFIG_PREEMPT
> > > > +       restore_irqs_notrace r9
> > > > +#endif
> > > > +       and     r2, r1, #7                      @ extract the length of the cache lines
> > > > +       add     r2, r2, #4                      @ add 4 (line length offset)
> > > > +       ldr     r4, =0x3ff
> > > > +       ands    r4, r4, r1, lsr #3              @ find maximum number on the way size
> > > > +       clz     r5, r4                          @ find bit position of way size increment
> > > > +       ldr     r7, =0x7fff
> > > > +       ands    r7, r7, r1, lsr #13             @ extract max number of the index size
> > > > +loop2:
> > > > +       mov     r9, r4                          @ create working copy of max way size
> > > > +loop3:
> > > > +       orr     r11, r10, r9, lsl r5            @ factor way and cache number into r11
> > > > +       orr     r11, r11, r7, lsl r2            @ factor index number into r11
> > > > +       mcr     p15, 0, r11, c7, c14, 2         @ clean & invalidate by set/way
> > > > +       subs    r9, r9, #1                      @ decrement the way
> > > > +       bge     loop3
> > > > +       subs    r7, r7, #1                      @ decrement the index
> > > > +       bge     loop2
> > > > +finished:
> > > > +       mov     r10, #0                         @ swith back to cache level 0
> > > > +       mcr     p15, 2, r10, c0, c0, 0          @ select current cache level in cssr 
> > > > +       dsb
> > > > +       isb
> > > 
> > > This code is already in the kernel in cache-v7.S, please use that.
> > > We are just adding the new LoUIS API that probably does what you
> > > want, even though for Tegra, that is an A9 based platform I fail to
> > > understand why Level of Coherency differs from L1.
> > > 
> > > Can you explain to me please why Level of Coherency (LoC) is != from L1
> > > on Tegra ?
> > > 
> > 
> > Thanks for introducing the new LoUIS cache API. Did LoUIS been changed
> > by other HW? I checked the new LoUIS API. If LoUIS == 0, it means inner
> > shareable then it do nothing just return. But I need to flush L1 data
> > cache here to sync the coherency before CPU be power gated. And disable
> > data cache before flush is needed.
> 
> I understand that, that's why I am asking. To me LoUIS and LoC should
> both be the same for A9 based platforms and they should both represent
> a cache level that *includes* L1.
> 
> Can you provide me with the CLIDR value for Tegra3 please ?
> 

I just checked the CLIDR of both Tegra20 and Tegra30. It's 0x09200003.
It looks I can use this new LoUIS api, right? :)

I will give it a try and update to next version. Thanks.

> > 
> > I can tell you the sequence that why we just do L1 data cache flush
> > here. Maybe I need to change the comment to "flush to point of
> > coherency" not "level of coherency".
> > 
> > For secondary CPUs:
> > * after cpu_suspend
> > * disable data cache and flush L1 data cache
>     ^(1)
> > * Turn off SMP coherency
>     ^(2)
> 
> Two steps above, one assembly function, no access to any data whatsoever
> please.
> 
OK. Will do this and update to next version.

> > * power gate CPU
> > 
> > For CPU0:
> > * outer_disable (flush and disable L2)
> 
> I guess L2 cannot be retained on Tegra ?
> 
Yes.

I will give it a test and update later.

Thanks,
Joseph