From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vitaly Andrianov Date: Wed, 18 Feb 2015 08:12:36 -0500 Subject: [U-Boot] [U-boot][PATCH] keystone2: add support for UART download In-Reply-To: References: <1424110975-1153-1-git-send-email-vitalya@ti.com> <54E24FDB.3070304@ti.com> <54E3C05D.2040908@ti.com> Message-ID: <54E48FC4.9010505@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 02/17/2015 05:47 PM, Nishanth Menon wrote: > On Tue, Feb 17, 2015 at 4:27 PM, Murali Karicheri wrote: >>>> is complete the boot-loader sets the PC to the first MSMC address >>>> 0x0c000000. The u-boot.bin is linked to the address 0x0c001000. >>> >>> why not just shift u-boot.bin to start of MSMC address? >> >> What is wrong with the current implementation? NAND and SPI NOR boot modes >> use the >> GPH headers that has the load address defined. But in the case of UART, RBL > > So it GPH header has the load address defined, it does mean that we > could infact change the start address to 0xc000000 (instead of current > 0xc001000) and appropriately update the GPH headers to point there? > that way we can use 0xc000000 without padding on UART, as well as use > the same in NAND/SPI as well? correct? > >> loads it to start of MSMC and adding 1K of NOP just avoid a jump instruction >> at >> the start of the memory to jump to 0xc001000. This way we can keep the same >> start address across all boot modes. > > Padding a 4kbytes (1K NOP at 32bits each) just because there is a > difference between linked address and start address in a specific mode > makes one wonder. This probably is not definitely a uniquely KS2 issue > - we probably have similar behavior on other platforms as well. what > if we chose a link address 2MB away (as an example)? agreed that the > specific usage has no such size story in place, but conceptually we > might be able to do better. > >>>> In order to use the u-boot.bin as an image for UART download, we need to >>>> add 4K zeros prefix that act as 1K NOP instructions before reaching >>>> 0xc001000. >>> >>> OR, add a relocation logic which saves the 1k NOP and resultant load time? >> >> What saving are you talking about? Miliseconds? seconds? > > Maintainability? lets say we change link address tomorrow, we have to > adjust padding appropriately, further we just dont need padding when > we can just relocate self by being position independent in the first > place!. > > we have learnt that over years OMAP3 link address has gone through a > few transitions as we discovered better ways to do things. doing > padding based on link address does, on the first look, seem > unnecessary, makes sense only if all of the following are wrong: > a) cannot change start address to the common start address for all boot modes. > b) cannot add relocation and position independent u-boot code. > > And even when we do need to add padding, it is not a good idea to hard > code the pad size, instead do it algorithmically (basically query the > start and add the delta) allowing changes to link address to be > something folks can do at a later point in time without > unintentionally breaking uart boot. > > --- > Regards, > Nishanth Menon > _______________________________________________ > U-Boot mailing list > U-Boot at lists.denx.de > http://lists.denx.de/mailman/listinfo/u-boot > As I've already mentioned this patch is not about improving or changing current u-boot.bin, but just providing a way to download it over UART port. Any improvements, if they are required, shall be done in other patches. Regards, -Vitaly