[U-Boot] [PATCH v1 0/7] imx: add USB Serial Download Protocol (SDP) support

[Stefan Agner]

Hi Eric,

On 2017-08-06 08:19, Eric Nelson wrote:
> Hi Stefan,
> 
> On 08/04/2017 04:38 PM, Stefan Agner wrote:
>> From: Stefan Agner <stefan.agner at toradex.com>
>>
>> This series adds NXP's Serial Download Protocol (SDP) support via
>> USB for SPL/U-Boot. It allows to download U-Boot via USB from a
>> (recovered) SPL using the same tools used to download SPL itself
>> (specifically imx_usb, but also sb_loader seems to work).
>>
> 
> Nice!
> 
>> The idea has been brought up when the first targets started to make
>> use of SPL for DDR initialization, see:
>> https://lists.denx.de/pipermail/u-boot/2015-July/220330.html
>>
> 
> There have been lots of discussions surrounding the use of SDP,
> and this seems to be a nice alternative to using the i.MX "plugin"
> mode that I explored a while back:
> 
> https://lists.denx.de/pipermail/u-boot/2017-July/thread.html#298266
> 

Hm, wasn't aware of that particular effort, thanks for pointing to it.
>From a quick glance, it did not work out so far, is this correct?

I looked into plugin mode also a little bit, but I did not continue to
look into it after reading this sentence in the i.MX 6 RM:

8.7 Plugin Image
The boot ROM detects the image type using the plugin flag of the boot
data structure (see
Boot Data Structure). If the plugin flag is 1, then the ROM uses the
image as a plugin
function. The function must initialize the boot device and copy the
program image to the
final location. At the end the plugin function must return with the
program image
parameters. (See High level boot sequence for details about boot flow).


So if SPL should work as a plugin as NXP defines it, SPL is supposed to
load the image from somewhere. The boot ROM then only takes care about
image verification and further boot steps, but it's the plugins job to
get the image from somewhere and store it in RAM.

Afact this is not really helpful in our case. We would want the boot ROM
to go through the boot sequence (again).

Unless returning an error/invalid image causes the boot ROM to go
through boot sequence again?


The nice thing with our own SDP implementation is we can reuse it even
from within U-Boot again, e.g. to download a kernel/initramfs....

>> The initial SDP implementation (patch 2) requires the payload to
>> have the imx specific headers (hence the move of the imx header
>> file in patch 1).
>>
>> Patch 3 extends image header support beyond the SDP specification,
>> specifically implements also support for U-Boot headers. This
>> allows to use the same SPL/U-Boot binaries for recovery as used on
>> the regular boot device (SD/eMMC). For that to work also the host
>> side imx_usb tools needed an extension, currently available here:
>>
>> https://github.com/toradex/imx_loader/tree/imx_usb_batch_mode_refactored
>>
>> The full patchset allows to download SPL and U-Boot over USB to a
>> target in recovery mode using the same usb_imx utility:
> 
> imx_usb?
> 

Yeah right, sorry.

>> The usb_imx utility also has a batch mode which allows to download
>> multiple artifacts with a single invocation. The details are
>> outlined in the imx_usb commit message:
>> https://github.com/toradex/imx_loader/commit/5434415d921f1cc4d22332d9558bed6d42db9f60
>>
>> In case this patchset gets accepted in U-Boot, I plan to push the
>> imx_usb changes upstream as well.
>>
> 
> Do you have numbers for how much code/data size this adds to SPL?
> 

Besides the protocol implementation also general USB (gadget) support is
required, hence it adds quite a bit.


Without USB Gadget/SDP support (Apalis iMX6 SPL):

$ arm-linux-gnueabihf-size spl/u-boot-spl
   text    data     bss     dec     hex filename
  24552    3808      92   28452    6f24 spl/u-boot-spl


With USB Gadget/SDP support:

$ arm-linux-gnueabihf-size spl/u-boot-spl
   text    data     bss     dec     hex filename
  42549    4679    1984   49212    c03c spl/u-boot-spl


> I believe some i.MX users have struggled to stay within the
> size of internal RAM.

Hm, I think the limit is somewhere around 64kiB? In our case we are
still well below...

--
Stefan