AT91: How copy kernel code to SRAM and execute?

[Jean-Christophe PLAGNIOL-VILLARD]

On 21:52 Sun 26 Feb     , ARM Linux wrote:
> On 2012-02-26 19:44, Jean-Christophe PLAGNIOL-VILLARD wrote:
> >On 18:37 Sun 26 Feb     , ARM Linux wrote:
> >>I am looking for some examples on how to copy a small piece of kernel code
> >>to internal SRAM and then execute it.
> >>
> >>Why?
> >>If you want to restart, you execute the "/sbin/reboot" command
> >>which will eventually call the "arch_reset" function, which in the AT91
> >>case will write to a "user reset" register.
> >>
> >>The problem is that the chip may reset in the middle of an SDRAM
> >>read transfer.
> >>The SDRAM will see it's clock stopped and will continue to drive the bus.
> >>
> >>When the ROM bootloader tries to access any boot memory (Parallel
> >>flash or NAND flash)
> >>on the parallel bus, there will be a bus conflict between the boot
> >>memory and the SDRAM,
> >>and the bootROM will not properly detect the boot program, and will enter
> >>an In System Programming mode.
> >>
> >>This is described in the SAM9G20 datasheet, but is probably valid
> >>for all older generation AT91 devices as well.
> >>
> >>The workaround seems to be to turn off the SDRAM and then do the reset.
> >>Obviously you cannot read instructions from SDRAM after it has been
> >>turned off.
> >>
> >	Which version of the kernel do you use?
> >
> On 2012-02-26 19:44, Jean-Christophe PLAGNIOL-VILLARD wrote:
> >On 18:37 Sun 26 Feb     , ARM Linux wrote:
> >>I am looking for some examples on how to copy a small piece of kernel code
> >>to internal SRAM and then execute it.
> >>
> >>Why?
> >>If you want to restart, you execute the "/sbin/reboot" command
> >>which will eventually call the "arch_reset" function, which in the AT91
> >>case will write to a "user reset" register.
> >>
> >>The problem is that the chip may reset in the middle of an SDRAM
> >>read transfer.
> >>The SDRAM will see it's clock stopped and will continue to drive the bus.
> >>
> >>When the ROM bootloader tries to access any boot memory (Parallel
> >>flash or NAND flash)
> >>on the parallel bus, there will be a bus conflict between the boot
> >>memory and the SDRAM,
> >>and the bootROM will not properly detect the boot program, and will enter
> >>an In System Programming mode.
> >>
> >>This is described in the SAM9G20 datasheet, but is probably valid
> >>for all older generation AT91 devices as well.
> >>
> >>The workaround seems to be to turn off the SDRAM and then do the reset.
> >>Obviously you cannot read instructions from SDRAM after it has been
> >>turned off.
> >>
> >	Which version of the kernel do you use?
> >
> >	There is no need to put the code in the sram, you just need to put the
> >	code in cached before shutdown the SDRAM/DDR
> >
> 
> The vanilla 2.6.30 from linux4sam, but it is using a patchset from a
> customer.
> I don't think it is an option to change kernel version right now.
> Cache is turned off in this version.
so turn it on run the code from sram is wrong solution here

I do not do this on mainline

just use the fix we use here

Best Regards,
J.