[U-Boot] [PATCH V12 08/14] Add cache functions to SPL for armv7

[Stefano Babic]

On 04/01/2012 12:33, Aneesh V wrote:
> Hi Stefano,
> 

Hi,

> On Wednesday 04 January 2012 09:25 AM, Stefano Babic wrote:
>> Signed-off-by: Stefano Babic<sbabic at denx.de>
>> CC: Tom Rini<tom.rini at gmail.com>
>> CC: Wolfgang Denk<wd at denx.de>
>> CC: Simon Schwarz<simonschwarzcor at gmail.com>
>> ---
>>
>> Changes since V11:
>>
>> - enable cache files in Makefile after checking build for OMAP4/5
> 
> How are you allocating memory for the page-tables(gd->tlb_addr)? Also
> we need to take care of the complexities when u-boot runs after SPL.

I know, and the patch can be considered a preparation for adding d-cache
later - dcache is not enabled at all in this patchset. At the moment,
cleanup_before_linux() is called as in U-Boot, but caches are already
disabled. I know memory for the page tables must be reserved, but this
part is not yet done.

> Please have a look at this.
> 
> http://article.gmane.org/gmane.comp.boot-loaders.u-boot/100012/match=spl+cache

I am aware of this. And this is also the reason I see caches as a
second-step approach. Firstly, we should have a way to boot linux
directly from SPL, without enabling cache. Then we have the possibility
to increase the mumber of our testers, because, as far as I know, only
me and Simon have tried with this patchset to get some measurement.

In my current tests on the twister board (AM3517 based), most time is
spent really to load the kernel (~2MB, with a lot of drivers..).
As answer to your point 1 in the previous thread, maybe it is really
worth to enable cache to speed up the loading part respecting enabling
DMA. Adding DMA means adding DMA support in each specific driver (NAND
vs MMC vs..), while with d-cache we have a solution working
independenlty from the supported media. But it makes sense to have a
large number of boards supporting direct booting before making some
wrong assumptions ;-)

Best regards,
Stefano Babic

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