[U-Boot] [PATCH 1/3] common/cmd_rsmode.c: add imx reset mode command

[Dirk Behme]

On 27.05.2012 19:16, Eric Nelson wrote:
> Hi Dirk,
>
> On 05/26/2012 11:04 PM, Dirk Behme wrote:
>> Hi Troy,
>>
>> On 26.05.2012 23:01, Troy Kisky wrote:
>>> This is useful for forcing the ROM's
>>> usb downloader to activate upon a watchdog reset.
>>> Or, you can boot from either SD Card.
>>
>> Thanks!
>>
>> Just for my understanding: Who will enable/run the watchdog reset?
>> It was my
>> understanding that after writing gpr9 and gpr10 someone has to
>> enable the
>> watchdog to execute the reset?
>>
> Or just issue the 'reset' command, so we can prevent the need to
> re-program the SPI ROM with the boot to SD shim with something like
> this:
>
> U-Boot> set bootcmd 'rsmode esdhc3 && reset' && saveenv
>
> I discussed this with Troy yesterday and would like to get some feedback
> from those most likely to use the features of this code.

I like this idea.

But I haven't looked into the detailed implementation of the 'reset' 
command for i.MX6. Does it run/execute the necessary watchdog reset?

> Troy's implementation exposes the internals and all of the power
> of the reset mode override feature. Through the 'rsmode' command,
> you can set up what happens during the next watchdog reset and then do
> something else.
>
> For instance, you could say 'rsmode esdhc1', set up the watchdog and
> then launch an O/S which should take over the watchdog. If something
> fails, the ROM will attempt to boot to esdhc1, providing a fallback
> mechanism of sorts.

What I read from above is that we need to flavors of the reset 
(watchdog setup) command? Or better: Two ways of enabling the watchdog 
for the two usage scenarios I read above:

Usage scenario 1: We wan't to reset/reboot as soon as possible after 
doing the rsmode command. This would be used as a replacement for what 
we use at the moment with the SabreLite boards: They boot from SPI 
NOR, but we like to switch as fast as possible to SD boot. This 
implies that the watchdog reset is needed as fast as possible after 
the rsmode command is done.

Usage scenario 2: This is what you describe above: Set the rsmode, set 
up the watchdog and let the OS take over the watchdog. This would 
imply a longer watchdog reset period, to give the OS some time to take 
over.

> While there may be some conditions under which this will be used,
> a few dominant use cases and these could be made simpler to understand
> and use.
>
> 1. Change 'rsmode' to 'rstmode'. I suspect that everyone will have
> an easier time understanding that the latter means 'reset mode'.

Yes, this sounds better :) I'm not sure about the naming conventions, 
but spending some additional characters to name it 'resetmode' would 
work, too?

> 2. Implement 'download_mode' or 'downusb' as a short-hand for the
> sequence:
>
> U-Boot> rsmode usb && reset
>
> This sequence will be executed mostly by those on this list and
> the abbreviation is worth the small addition of code.
>
> I already have 'down' in muscle memory and using it will ease
> the pain for the (hopefully short) interval while I'm using
> both the Freescale 2009.08 code base and mainline.
>
> 3. Similarly, implement 'bootsd' or 'bootmmc' with a parameter that
> matches the SD card naming used by other U-Boot commands.
>
> How many of you know without grepping or pulling up a schematic
> which device corresponds to 'mmc 0'?
>
> It seems more intuitive to issue this command:
>
> U-Boot> bootmmc 0
>
> instead of this:
>
> U-Boot> rsmode esdhc3 && reset
>
> 4. Same rationale for 'bootsata'.
>
> 5. Allow boards to say which devices are even exposed in their config
> headers. i.e.
> #define BOARD_HAS_ESDHC3
>
> ...
>
> #ifdef BOARD_HAS_ESDHC3
> {"esdhc1", mkval(0x40, 0x20, 0x00, 0x12)},
> #endif
>
> This will allow a form of self-documentation when running 'rsmode'
> with no parameters.

This sounds good, too.

> I doubt any board supports all of the boot options.
>
> Let us know your thoughts on this and thanks for the code Troy!

Yes, many thanks for the code!

I think we should clarify how the watchdog is handled in this 
scenario. By the reset command? And do we need a 'long timeout' and a 
'immediate timeout' watchdog?

Best regards

Dirk