From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aneesh V Date: Mon, 06 Feb 2012 19:49:51 +0530 Subject: [U-Boot] Skipping relocation RAM to RAM, esp. on i.MX6? In-Reply-To: References: <4F2B8BD1.2030009@de.bosch.com> <4F2CF73F.2090407@ti.com> Message-ID: <4F2FE187.7040505@ti.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de On Sunday 05 February 2012 11:49 AM, Simon Glass wrote: > Hi, > > On Sat, Feb 4, 2012 at 1:15 AM, Aneesh V wrote: >> Hi Dirk, >> >> >> On Friday 03 February 2012 12:55 PM, Dirk Behme wrote: >>> >>> Hi, >>> >>> on i.MX6 devices, e.g. ARM2 or SabreLite, the ROM boot loader copies the >>> U-Boot image from the boot device, e.g. the SD card, to the main memory. >>> This does mean that U-Boot is started in RAM. >>> >>> With this, one might wonder why any relocation RAM -> RAM is done anyway >>> and if this could be skipped? >>> >>> Looking into the details shows that board_init_f() in >>> arch/arm/lib/board.c and relocate_code() in arch/arm/cpu/armv7/start.S >>> [1] are involved in this. >>> >>> In board_init_f() the relocation destination address 'addr' is >>> calculated. This is basically at the end of the available RAM (- some >>> space for various stuff like TLB tables etc.). At SabreLite this results >>> in 0x4FF8D000. >>> >>> By the boot loader, the U-Boot is loaded to >>> >>> CONFIG_SYS_TEXT_BASE 0x17800000 >>> >>> This results in relocate_code() copying U-Boot from RAM 0x17800000 to >>> RAM 0x4FF8D000. >>> >>> Setting CONFIG_SYS_TEXT_BASE to the relocation destination address >>> 0x4FF8D000 does avoid the (unnecessary?) copy by >>> >>> cmp r0, r6 >>> moveq r9, #0 /* no relocation. relocation offset(r9) = 0 */ >>> beq clear_bss /* skip relocation */ >>> >>> in relocate_code(). >>> >>> But: >>> >>> 1) The resulting image still runs without the relocation >>> (CONFIG_SYS_TEXT_BASE 0x4FF8D000). But e.g. the U-Boot command line >>> doesn't work properly any more. Most probably this is because not only >>> the copy is skipped by the 'beq clear_bss', but the whole 'fix .rel.dyn >>> relocations' is skipped too. >>> >>> 2) It's hard to set CONFIG_SYS_TEXT_BASE at compile time to the >>> relocation address calculated at runtime in board_init_f() due to the >>> amount of #ifdef and runtime calculation done there. So finding a >>> generic approach which could easily defined in the config files to avoid >>> the relocation seems difficult. >> >> >> I haven't really completely read your mail. But here is an >> implementation I had provided long time back for ARM. But Wolfgang >> didn't want to take it. You can see the patch and the following >> discussion in this thread: >> >> http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/96352 > > From your patch Aneesh I evolved something that I still use - it deals > with the case where malloc cannot fit below the text area. > > I find any sort of messing with the ICE startup a pain - although I > have often been able to script it. But for me I need to attach the > device tree to the binary and a few other things so I might as well > disable relocation at the same time. It also allows me to debug > seamlessly in board_init_f() as well as afterwards. > > I will send a patch. Great! > > It would be good to get something in mainline despite the > protestations, if only to avoid all the work that people have to do to > figure out this problem. I am always in favor of that:) best regards, Aneesh