Re: [PATCH 0/2] Command for entering mask rom USB download mode

["Michal Suchánek" <msuchanek@suse.de>]

On Sun, Jul 03, 2022 at 06:26:22PM -0500, Samuel Holland wrote:
> Hi Michal,
> 
> On 7/3/22 2:20 PM, Michal Suchanek wrote:
> > 
> > Hello,
> > 
> > many ARM SoCs have a mask rom feature that provides interface for
> > downloading firmware over USB.
> > 
> > Downstream rockchip u-boot has 'brom' or 'rbrom' command for this
> > purpose, and downstream sunxi u-boot provides 'efex' command. p-boot has
> > code for entering FEL on A64 SoC.
> > 
> > With this patch I am able to activate the USB downloader on a rk3399 but
> > the rkflashtool fails to communicate with the device. On a H2+ I can get
> > into the FEL mode and get flash parameters. YMMV
> > 
> > I don't have any great idea how to structure this so that the command
> > does not need platform-specific code. Is there an example of a command
> > that has platform-specific implementations?
> 
> Generally you would do this by having the driver interact with some DM uclass.
> Platforms may or may not provide a driver implementing that uclass; the details
> are hidden behind the uclass's interface. All the command has to do is search
> for a DM device by uclass, and if one is found, call some operation on it.
> 
> In this case, UCLASS_REBOOT_MODE already exists. It sounds like what we need is
> the inverse of dm_reboot_mode_update() -- a function that takes a string and
> programs the device with the corresponding mode value.
> 
> To be generic, you could call this function from do_reset() if some positional
> argument is provided, allowing usage like "reset bootloader" or "reset fel".
> 
> Rockchip platforms already have syscon-reboot-mode hooked up in their
> devicetrees. The driver for this should be trivial.
> 
> Allwinner platforms would need to add a nvmem-reboot-mode node, and a bit more
> driver infrastructure. U-Boot does not have NVMEM uclass, so you would need to
> add one or reuse UCLASS_MISC.

Not sure I understand the DM enough but as firt step I can at least hook
it to the do_reset function.

Thanks

Michal