Re: [Linux-stm32] [PATCH v2 00/14] Introduce STM32MP1 RCC in secured mode

[Marek Vasut]

On 3/11/21 7:10 PM, Alexandre TORGUE wrote:
> Hi Guys
>
> On 3/11/21 5:11 PM, Marek Vasut wrote:
> > On 3/11/21 3:41 PM, Ahmad Fatoum wrote:
> > > Hello,
> >
> > Hi,
> >
> > > On 11.03.21 15:02, Alexandre TORGUE wrote:
> > > > On 3/11/21 12:43 PM, Marek Vasut wrote:
> > > > > On 3/11/21 9:08 AM, Alexandre TORGUE wrote:
> > > > > > 1- Break the current ABI: as soon as those patches are merged, 
> > > > > > stm32mp157c-dk2.dtb will impose to use
> > > > > > A tf-a for scmi clocks. For people using u-boot spl, the will have 
> > > > > > to create their own "no-secure" devicetree.
> > > > >
> > > > > NAK, this breaks existing boards and existing setups, e.g. DK2 that 
> > > > > does not use ATF.
> > > > >
> > > > > > 2-As you suggest, create a new "secure" dtb per boards (Not my 
> > > > > > wish for maintenance perspectives).
> > > > >
> > > > > I agree with Alex (G) that the "secure" option should be opt-in.
> > > > > That way existing setups remain working and no extra requirements 
> > > > > are imposed on MP1 users. Esp. since as far as I understand this, 
> > > > > the "secure" part isn't really about security, but rather about 
> > > > > moving clock configuration from Linux to some firmware blob.
> > > > >
> > > > > > 3- Keep kernel device tree as they are and applied this secure 
> > > > > > layer (scmi clocks phandle) thanks to dtbo in
> > > > > > U-boot.
> > > > >
> > > > > Is this really better than
> > > > > #include "stm32mp15xx-enable-secure-stuff.dtsi"
> > > > > in a board DT ? Because that is how I imagine the opt-in "secure" 
> > > > > option could work.
> > > >
> > > > Discussing with Patrick about u-boot, we could use dtbo application 
> > > > thanks to extlinux.conf. BUT it it will not prevent other case (i.e. 
> > > > TF-A which jump directly in kernel@). So the "least worst" solution 
> > > > is to create a new "stm32mp1257c-scmi-dk2 board which will overload 
> > > > clock entries with a scmi phandle (as proposed by Alex).
> > >
> > > I raised this issue before with your colleagues. I still believe the 
> > > correct way
> > > would be for the TF-A to pass down either a device tree or an overlay 
> > > with the
> > > actual settings in use, e.g.:
> > >
> > >    - Clocks/Resets done via SCMI
> > >    - Reserved memory regions
> > >
> > > If TF-A directly boots Linux, it can apply the overlay itself, 
> > > otherwise it's
> > > passed down to SSBL that applies it before booting Linux.
> >
> > That sounds good and it is something e.g. R-Car already does, it 
> > merges DT fragment from prior stages at U-Boot level and then passes 
> > the result to Linux.
> >
> > So on ST hardware, the same could very well happen and it would work 
> > for both non-ATF / ATF / ATF+TEE options.
>
> Even this solution sounds good but we are currently not able to do it in 
> our TF-A/u-boot so not feasible for the moment.

Why not ? U-Boot is perfectly capable of merging prior stage DT and DT 
loaded from elsewhere. See R-Car3 for example.

> So we have to find a 
> solution for now. Create a new dtb can be this solution. Our internal 
> strategy is to use scmi on our official ST board. It will be a really 
> drawback to include a "no-scmi.dtsi" in DH boards (for example) and to 
> create a stm32mp157c-noscmi-dk2.dts ?

I would highly prefer the SCMI to be opt-in, not opt-out.

But still, isn't it possible to auto-detect the board configuration in 
Linux and pick the clock enumeration based on that automatically ?