[U-Boot] [U-boot][PATCH] keystone2: add support for UART download

[Nishanth Menon]

On 02/18/2015 09:35 AM, menon.nishanth at gmail.com wrote:
> On Wed, Feb 18, 2015 at 7:12 AM, Vitaly Andrianov <vitalya at ti.com> wrote:
>>
>>
>> On 02/17/2015 05:47 PM, Nishanth Menon wrote:
>>>
>>> On Tue, Feb 17, 2015 at 4:27 PM, Murali Karicheri <m-karicheri2 at ti.com>
>>> 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.
>>>
> [...]
>> 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.
> 
> 
> We would not need a u-boot.uart if current u-boot.bin can do the job, do we?
> 

I just noticed this:
http://git.denx.de/?p=u-boot.git;a=blob;f=doc/README.arm-relocation;h=645b3746c8a88fe25f7c9a33cd9b8b17aa7b5a57;hb=HEAD#l37

without relocation capability, a board might be liable for removal?
-- 
Regards,
Nishanth Menon