Re: [PATCH] ARM: bcm281xx: Add L2 support for Rev A2 chips

[Christian Daudt]

Hi Will,
 Thanks for your feedback. See below for answers.

On 13-05-01 03:37 AM, Will Deacon wrote:
> Hi Christian,
>
> Thanks for CC'ing me.
>
> On Tue, Apr 30, 2013 at 07:38:09PM +0100, Christian Daudt wrote:
> > Rev A2 SoCs have an unorthodox memory re-mapping and this needs
> > to be reflected in the cache operations.
> > This patch adds new outer cache functions for the l2x0 driver
> > to support this SoC revision. It also adds a new compatible
> > value for the cache to enable this functionality.
> This is a pretty weird thing you've managed to build here...
No argument here.
> > diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c
> > index c465fac..6edba13 100644
> > --- a/arch/arm/mm/cache-l2x0.c
> > +++ b/arch/arm/mm/cache-l2x0.c
> > @@ -523,6 +523,162 @@ static void aurora_flush_range(unsigned long start, unsigned long end)
> >   	}
> >   }
> >   
> > +/*
> > + * For certain Broadcom SoCs, depending on the address range, different offsets
> > + * need to be added to the address before passing it to L2 for
> > + * invalidation/clean/flush
> > + *
> > + * Section Address Range              Offset        EMI
> > + *   1     0x00000000 - 0x3FFFFFFF    0x80000000    VC
> > + *   2     0x40000000 - 0xBFFFFFFF    0x40000000    SYS
> > + *   3     0xC0000000 - 0xFFFFFFFF    0x80000000    VC
> Hmm, so am I right in thinking that the `Broadcom addresses' for section 1
> and 2 overlap? It would also be worth describing which physical addresses
> Linux actually wants to use; where is the memory in the physical memory map
> for devices with this L2 controller?
I've clarified this internally. Yes, there is an overlap, and because of 
that section 1 can't actually be used. I'm going to clear up the patch 
to remove the section one calculations to simplify it.
> > + * When the start and end addresses have crossed two different sections, we
> > + * need to break the L2 operation into two, each within its own section.
> > + * For example, if we need to invalidate addresses starts at 0xBFFF0000 and
> > + * ends at 0xC0001000, we need do invalidate 1) 0xBFFF0000 - 0xBFFFFFFF and 2)
> > + * 0xC0000000 - 0xC0001000
> > + *
> > + * Note 1:
> > + * By breaking a single L2 operation into two, we may potentially suffer some
> > + * performance hit, but keep in mind the cross section case is very rare
> > + *
> > + * Note 2:
> > + * We do not need to handle the case when the start address is in
> > + * Section 1 and the end address is in Section 3, since it is not a valid use
> > + * case
> > + */
> > +
> > +#define BCM_VC_EMI_SEC1_START_ADDR    0x00000000UL
> > +#define BCM_VC_EMI_SEC1_END_ADDR      0x3FFFFFFFUL
> > +#define BCM_SYS_EMI_START_ADDR        0x40000000UL
> > +#define BCM_SYS_EMI_END_ADDR          0xBFFFFFFFUL
> > +#define BCM_VC_EMI_SEC3_START_ADDR    0xC0000000UL
> > +#define BCM_VC_EMI_SEC3_END_ADDR      0xFFFFFFFFUL
> Seems a bit odd defining the END_ADDRs here, I'd just use strict '<' against
> the start of the next section in your code.
Makes sense. Removed.
> > +#define BCM_SYS_EMI_OFFSET            0x40000000UL
> > +#define BCM_VC_EMI_OFFSET             0x80000000UL
> > +
> > +static inline int bcm_addr_is_sys_emi(unsigned long addr)
> > +{
> > +	return (addr >= BCM_SYS_EMI_START_ADDR) &&
> > +		(addr <= BCM_SYS_EMI_END_ADDR);
> > +}
> > +
> > +static inline unsigned long bcm_l2_phys_addr(unsigned long addr)
> > +{
> > +	if (bcm_addr_is_sys_emi(addr))
> > +		return addr + BCM_SYS_EMI_OFFSET;
> > +	else
> > +		return addr + BCM_VC_EMI_OFFSET;
> > +}
> > +
> > +static void bcm_inv_range(unsigned long start, unsigned long end)
> > +{
> > +	unsigned long new_start, new_end;
> > +
> > +	if (unlikely(end <= start))
> > +		return;
> > +
> > +	new_start = bcm_l2_phys_addr(start);
> > +	new_end = bcm_l2_phys_addr(end);
> > +
> > +	/* normal case, no cross section between start and end */
> > +	if (likely((bcm_addr_is_sys_emi(start) && bcm_addr_is_sys_emi(end)) ||
> > +		(!bcm_addr_is_sys_emi(start) && !bcm_addr_is_sys_emi(end)))) {
> You could avoid evaluating bcm_addr_is_sys_emi twice for each address. In
> fact, you know start < end, so you just need to check start >= EMI_START and
> end < EMI_END.
This test is to confirm that the range is completely within 1 section, 
so a single test won't do that - with the test as-is, the code after 
this 'if' already knows that there is section overlap. But I'll be 
removing section 1 handling and that will simplify things.

 thanks,
   csd


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