[U-Boot] [PATCH 11/14] sunxi: Fill memory before comparing it when doing dram init on sun6i

[Siarhei Siamashka <siarhei.siamashka@gmail.com>]

On Thu, 18 Dec 2014 19:12:13 +0000
Ian Campbell <ijc@hellion.org.uk> wrote:

> On Tue, 2014-12-16 at 21:31 +0100, Hans de Goede wrote:
> > The sun8i boot0 code fills the DRAM with a "random" pattern before comparing
> > it at different offsets to do columns, etc. detection. The sun6i boot0 code
> > does not do it, but it seems like a good idea to do this regardless.
> 
> Is this the right way round? The existing sun6i code (which you are
> moving here) seems to _rely_ on something having written a useful
> pattern, which I would have assumed to have been boot0. Or else how does
> it work now? Chance?

It appears that this code is just trying to find the first address line,
which is not connected anywhere. If the address line is not connected,
then having the corresponding bit set or clear in the memory address
does not matter and we are effectively accessing the same location.

Both sun6i and sun8i code is incorrect and only works because of relying
on luck.

The sun6i code is incorrect because it is just reading memory without
initializing it at all. Probably relying on having some unique garbage
there in a natural way.

The newer sun8i code is still incorrect because it is not safeguarding
against accidentally encountering the same test pattern at an unrelated
memory location. Yes, the probability is extremely low, but still not
zero. 

It's a good idea to have a look at the 'get_ram_size' function for
the inspiration.


> > The new mctl_mem_fill function this introduces is added as an inline helper
> > in dram.h, so that it can be shared with the sun8i dram code.
> > 
> > While at it move mctl_mem_matches to dram.h for re-use in sun8i too.
> > 
> > Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> > ---
> >  arch/arm/cpu/armv7/sunxi/dram_sun6i.c  | 15 +--------------
> >  arch/arm/include/asm/arch-sunxi/dram.h | 29 +++++++++++++++++++++++++++++
> >  2 files changed, 30 insertions(+), 14 deletions(-)
> > 
> > diff --git a/arch/arm/cpu/armv7/sunxi/dram_sun6i.c b/arch/arm/cpu/armv7/sunxi/dram_sun6i.c
> > index e1670e5..4675c48 100644
> > --- a/arch/arm/cpu/armv7/sunxi/dram_sun6i.c
> > +++ b/arch/arm/cpu/armv7/sunxi/dram_sun6i.c
> > @@ -326,20 +326,6 @@ static void mctl_port_cfg(void)
> >  	writel(0x00000307, &mctl_com->mbagcr[5]);
> >  }
> >  
> > -static bool mctl_mem_matches(u32 offset)
> > -{
> > -	const int match_count = 64;
> > -	int i, matches = 0;
> > -
> > -	for (i = 0; i < match_count; i++) {
> > -		if (readl(CONFIG_SYS_SDRAM_BASE + i * 4) ==
> > -		    readl(CONFIG_SYS_SDRAM_BASE + offset + i * 4))
> > -			matches++;
> > -	}
> > -
> > -	return matches == match_count;
> > -}
> > -
> >  unsigned long sunxi_dram_init(void)
> >  {
> >  	struct sunxi_mctl_com_reg * const mctl_com =
> > @@ -391,6 +377,7 @@ unsigned long sunxi_dram_init(void)
> >  		    MCTL_CR_BANK(1) | MCTL_CR_RANK(1));
> >  
> >  	/* Detect and set page size */
> > +	mctl_mem_fill();
> >  	for (columns = 7; columns < 20; columns++) {
> >  		if (mctl_mem_matches(1 << columns))
> >  			break;
> > diff --git a/arch/arm/include/asm/arch-sunxi/dram.h b/arch/arm/include/asm/arch-sunxi/dram.h
> > index 18924f5..0bf718c 100644
> > --- a/arch/arm/include/asm/arch-sunxi/dram.h
> > +++ b/arch/arm/include/asm/arch-sunxi/dram.h
> > @@ -22,6 +22,8 @@
> >  #include <asm/arch/dram_sun4i.h>
> >  #endif
> >  
> > +#define MCTL_MEM_FILL_MATCH_COUNT 64
> > +
> >  unsigned long sunxi_dram_init(void);
> >  
> >  /*
> > @@ -37,4 +39,31 @@ static inline void mctl_await_completion(u32 *reg, u32 mask, u32 val)
> >  	}
> >  }
> >  
> > +/*
> > + * Fill beginning of DRAM with "random" data for mctl_mem_matches()
> > + */
> > +static inline void mctl_mem_fill(void)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < MCTL_MEM_FILL_MATCH_COUNT; i++)
> > +		writel(0xaa55aa55 + i, CONFIG_SYS_SDRAM_BASE + i * 4);
> > +}
> > +
> > +/*
> > + * Test if memory at offset offset matches memory at begin of DRAM
> > + */
> > +static inline bool mctl_mem_matches(u32 offset)
> > +{
> > +	int i, matches = 0;
> > +
> > +	for (i = 0; i < MCTL_MEM_FILL_MATCH_COUNT; i++) {
> > +		if (readl(CONFIG_SYS_SDRAM_BASE + i * 4) ==
> > +		    readl(CONFIG_SYS_SDRAM_BASE + offset + i * 4))
> > +			matches++;
> > +	}
> > +
> > +	return matches == MCTL_MEM_FILL_MATCH_COUNT;
> > +}
> > +
> >  #endif /* _SUNXI_DRAM_H */

-- 
Best regards,
Siarhei Siamashka