[U-Boot-Users] [PATCH] ppc4xx: Don't use last 256 bytes of SDRAM, workaround for 440EPx CHIP 11 errata

[Larry Johnson <lrj@acm.org>]

Stefan Roese wrote:
> On Thursday 27 March 2008, Larry Johnson wrote:
>> Yes, we normally use ECC modules in our testing.  I've been looking at a
>> patch for "initdram()" Denali SPD, but I've been waiting to see how your
>> "CFG_MEM_TOP_HIDE" patch would turn out.
>>
>> As things stand now, can I assume that boards using the Denali SPD will
>> also define "CFG_MEM_TOP_HIDE", and therefore initdram() should continue
>> to return the full size of the memory?
> 
> Correct.
> 
>> The only place that the last 256 bytes of memory are touched is when
>> "dflush()" is called to zero the SDRAM.
> 
> To be more specific, in the dcbz_area() call.
> 
>> This does not cause a Machine 
>> Check interrupt.  I am guessing that all the writes from "dflush()" are
>> aligned, and therefore there are no burst that access beyond the end of
>> of the SDRAM memory space.  If so, then my inclination is not to change
>> this part of the code.  Does this make sense?
> 
> I recommend to change it this way:
> 
>         /* Zero the memory */
>         debug("Zeroing SDRAM...");
> -       dcbz_area(CFG_SDRAM_BASE, dram_size);
> +       dcbz_area(CFG_SDRAM_BASE, dram_size - CFG_MEM_TOP_HIDE);
>         dflush();
> 
> And perhaps put something like:
> 
> #ifndef CFG_MEM_TOP_HIDE
> #error "Please define CFG_MEM_TOP_HIDE (see README) in your board config 
> file!"
> #endif
> 
> at the top of the file. What do you think?
> 
> Best regards,
> Stefan

That sound fine, I'll try to get a patch out soon.

Best regards,
Larry