Re: [PATCH 4/4] ARM: dts: stm32mp: add bootrom serial (DFU) reboot mode

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Sascha,

On 09.08.22 11:49, Sascha Hauer wrote:
> On Tue, Aug 09, 2022 at 08:29:38AM +0200, Ahmad Fatoum wrote:
>> The same register we use for the reboot mode communication between Linux
>> and barebox is also sampled by the bootrom. If the lowest 16 bits of it
>> are 0x00FF, the bootrom will enter DFU mode. Add the appropriate
>> reboot-mode, but with a barebox, prefix, so Linux doesn't automatically
>> provide it to userspace along with the existing loader and recovery
>> modes.
> 
> Why do we need to prevent Linux from providing dfu mode to userspace?
> Isn't that a vlid usecase?

It is, but I don't want a barebox update to add this feature by default.
So, communication with BootROM = not exported by default
Communication with Linux = exported by default

and this can be overridden on a per-board basis via device tree.
We do this likewise for the i.MX6 and i.MX8 where we have
barebox,syscon-reboot-mode which isn't processed by Linux, but we
can't use this here because the same register is used for both
modes of communication.

Cheers,
Ahmad

> 
> Sascha
> 
>>
>> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
>> ---
>>  arch/arm/dts/stm32mp151.dtsi | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/dts/stm32mp151.dtsi b/arch/arm/dts/stm32mp151.dtsi
>> index ed7cf6192bea..ac6536a556a9 100644
>> --- a/arch/arm/dts/stm32mp151.dtsi
>> +++ b/arch/arm/dts/stm32mp151.dtsi
>> @@ -41,9 +41,10 @@
>>  	reboot_mode_tamp: reboot-mode {
>>  		compatible = "syscon-reboot-mode";
>>  		offset = <0x150>; /* reg20 */
>> -		mask = <0xff>;
>> +		mask = <0xffff>;
>>  		mode-normal = <0>;
>>  		mode-loader = <0xBB>;
>>  		mode-recovery = <0xBC>;
>> +		barebox,mode-serial = <0xFF>;
>>  	};
>>  };
>> -- 
>> 2.30.2
>>
>>
>>
> 


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