[U-Boot] [PATCH v3 1/4] mips: add base support for atheros ath79 based SOCs

[Marek Vasut]

On Saturday, December 26, 2015 at 07:29:51 PM, Wills Wang wrote:
> WASP is ar9341.

Please do not top post.

Did you try if the memory is accessible on your platform ? AR9331 I have here 
has the SRAM at 0xbd007000 , just like that machine in [1] .

> On 12/27/2015 02:17 AM, Marek Vasut wrote:
> > On Saturday, December 26, 2015 at 06:35:35 PM, Marek Vasut wrote:
> >> On Saturday, December 26, 2015 at 04:48:57 PM, Wills Wang wrote:
> >> 
> >> [...]
> >> 
> >>>> The SPI flash is an IP block which just maps the SPI NOR into the
> >>>> address space, it doesn't use the CPU cache at all.
> >>>> 
> >>>> Maybe you don't even need to lock cachelines though, the AR9331 should
> >>>> have some internal SRAM, so just use that for stack. Do you have a
> >>>> proper datasheet for the Atheros MIPS chips ? I have some 320 pages
> >>>> datasheet for AR9331.
> >>> 
> >>> I don't find any description about internal SRAM in public datasheet.
> >>> About mapping SPI flash, there is a doubt, who fetch the instruction
> >>> from the SPI Nor flash to CPU pipe line when chip boot from SPI flash?
> >>> I guess that ROM code handle cache exception and load instruction/date
> >>> from SPI flash into cache.
> >> 
> >> I just pulled out the SPI NOR from the Arduino Yun I have here and
> >> connected an FPGA with SPI NOR emulator in there. All the chip does is
> >> it issues the fastread opcode to the SPI NOR when it boots. It does the
> >> same thing if you access the 0x9f000000..0x9fxxxxxx address range from
> >> the ancient U-Boot 1.1.x.
> >> 
> >> My impression is that the SPI NOR controller in the chip does a mapping
> >> between the SPI NOR and the memory mapped access to the 0x9fxxxxxx
> >> range. There is no caching involved in that, all of this is done
> >> internally in the SPI NOR block.
> >> 
> >> The mips24kc core should support locking cache lines , so if the SRAM is
> >> not available, this would have to do.
> > 
> > Ha, look at this [1]. risk @ #openwrt-devel at freenode pointed this
> > location out (thanks!)
> > 
> > [1] https://github.com/pepe2k/u-boot_mod/blob/master/u-
> > boot/cpu/mips/start.S#L652
> > 
> > Best regards,
> > Marek Vasut

Best regards,
Marek Vasut