linux-kernel - Re: [PATCH] devicetree: zynqmp.dtsi: Add bootmode selection support

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Date:   Thu, 20 Feb 2020 07:56:27 +0100
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     Vesa Jääskeläinen <dachaac@...il.com>,
        robh+dt@...nel.org, michal.simek@...inx.com, mark.rutland@....com,
        devicetree@...r.kernel.org
CC:     m.tretter@...gutronix.de, nava.manne@...inx.com,
        rajan.vaja@...inx.com, manish.narani@...inx.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] devicetree: zynqmp.dtsi: Add bootmode selection support

On 19-02-2020 19:23, Vesa Jääskeläinen wrote:
> Hi Mike,
> 
> On 19.2.2020 14.20, Mike Looijmans wrote:
>> Add bootmode override support for ZynqMP devices. Allows one to select
>> a boot device by running "reboot qspi32" for example. Activate config
>> item CONFIG_SYSCON_REBOOT_MODE to make this work.
>>
>> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
>> ---
>>   arch/arm64/boot/dts/xilinx/zynqmp.dtsi | 24 ++++++++++++++++++++++++
>>   1 file changed, 24 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/xilinx/zynqmp.dtsi 
>> b/arch/arm64/boot/dts/xilinx/zynqmp.dtsi
>> index 26d926eb1431..4c38d77ecbba 100644
>> --- a/arch/arm64/boot/dts/xilinx/zynqmp.dtsi
>> +++ b/arch/arm64/boot/dts/xilinx/zynqmp.dtsi
>> @@ -246,6 +246,30 @@
>>               };
>>           };
>> +        /* Clock and Reset control registers for LPD */
>> +        lpd_apb: apb@...e0000 {
>> +            compatible = "syscon", "simple-mfd";
>> +            reg = <0x0 0xff5e0000 0x0 0x400>;
>> +            reboot-mode {
>> +                compatible = "syscon-reboot-mode";
>> +                offset = <0x200>;
>> +                mask = <0xf100>;
>> +                /* Bit(8) is the "force user" bit */
>> +                mode-normal = <0x0000>;
>> +                mode-psjtag = <0x0100>;
>> +                mode-qspi24 = <0x1100>;
>> +                mode-qspi32 = <0x2100>;
>> +                mode-sd0    = <0x3100>;
>> +                mode-nand   = <0x4100>;
>> +                mode-sd1    = <0x6100>;
>> +                mode-emmc   = <0x6100>;
>> +                mode-usb0   = <0x7100>;
>> +                mode-pjtag0 = <0x8100>;
>> +                mode-pjtag1 = <0x9100>;
>> +                mode-sd1ls  = <0xe100>;
> 
> This kinda looks a bit misuse of reboot mode support.
> 
> Usually you are signal with reboot-mode that you want to do factory reset, 
> enter recovery mode or such things.
> 
> Now this signaling here is telling that this is used for selecting from what 
> device to boot from.

On the ZynqMP this is the only way to communicate with the ROM.

> Another problem is that this now modifies all Xilinx Zynq MPSoCs which is 
> kinda wrong. This behavior should really be product/board specific and not 
> common for all boards -- undoing this in product/board is somewhat cumbersome. 

The boot mode setting is in the SOC, and is not board specific. The ROM 
interprets this field. The only board specific thing is that you may not 
actually have a NAND chip attached to it.

My idea was that a board could easily add say 'mode-recovery=<0x2100>;' to 
make the QPSI boot the method of recovery. The bootloader also has access to 
this register, so it can see that there was a boot mode override in effect.

> Now this change hijacks the "reboot <arg>" with this behavior which is not so 
> nice.

If anyone has a better suggestion as to where this should go, I'd be more than 
happy to hear about it. It's the only interface that I could find in the 
kernel to attach a bootmode override to.