[PATCH 1/2] fsl-layerscape: add dtb overlay feature

[Sahil Malhotra (OSS)]

Hi Michael,

Gentle reminder on this patch set.

Regards,
Sahil Malhotra
> -----Original Message-----
> From: Sahil Malhotra (OSS)
> Sent: Friday, February 4, 2022 4:58 PM
> To: Michael Walle <michael at walle.cc>; Sahil Malhotra (OSS)
> <sahil.malhotra at oss.nxp.com>
> Cc: ZHIZHIKIN Andrey <andrey.zhizhikin at leica-geosystems.com>; Clément
> Faure <clement.faure at nxp.com>; Gaurav Jain <gaurav.jain at nxp.com>;
> Pankaj Gupta <pankaj.gupta at nxp.com>; Priyanka Jain
> <priyanka.jain at nxp.com>; u-boot at lists.denx.de; Varun Sethi
> <V.Sethi at nxp.com>; Ye Li <ye.li at nxp.com>
> Subject: RE: [PATCH 1/2] fsl-layerscape: add dtb overlay feature
> 
> Hi Michael,
> 
> Sorry for delayed response.
> Please find my response inline.
> 
> > -----Original Message-----
> > From: Michael Walle <michael at walle.cc>
> > Sent: Thursday, January 6, 2022 1:10 PM
> > To: Sahil Malhotra (OSS) <sahil.malhotra at oss.nxp.com>
> > Cc: ZHIZHIKIN Andrey <andrey.zhizhikin at leica-geosystems.com>; Clément
> > Faure <clement.faure at nxp.com>; Gaurav Jain <gaurav.jain at nxp.com>;
> > Pankaj Gupta <pankaj.gupta at nxp.com>; Priyanka Jain
> > <priyanka.jain at nxp.com>; u-boot at lists.denx.de; Varun Sethi
> > <V.Sethi at nxp.com>; Ye Li <ye.li at nxp.com>
> > Subject: Re: [PATCH 1/2] fsl-layerscape: add dtb overlay feature
> >
> > Hi Sahil,
> >
> > Am 2022-01-06 07:09, schrieb Sahil Malhotra (OSS):
> >
> > >> I don't know I follow. u-boot and linux should have the same device
> > >> tree; regardless if that device is used or not. So applying the
> > >> overlay just for linux isn't enough here.
> > > Ok, I don't think that as of now, in all platforms uboot and linux
> > > have same devie tree.
> >
> > That doesn't mean it is ok to diverge again. I put a lot of effort in
> > syncing uboot's LS1028A device tree with linux.
> Yes, that’s true we should not diverge again if they are already synced.
> 
> 
> > > But I will try to address your concern, but I don’t know how to
> > > apply overlay to dtb which is embedded in u-boot binary, Can you
> > > please point me to one reference which is doing this thing, I will
> > > take reference from there.
> >
> > Sorry I can't advise you with that. There is board_fix_fdt() maybe
> > that will help. But I'm not conviced this is the correct approach, see below.
> Ok, I looked at the board_fix_fdt() and in that we can put the code for
> modifying the uboot DTB.
> But the same overlay which we are going to apply on linux DTB should get
> applied On uboot DTB, and that can happen only when we have same DTBs
> both in Linux and u-boot.
> 
> I checked the uboot and Linux DTBs for LS platforms, except LS1028, all other
> platforms have a lot of difference in them.
> 
> So we will not be able to apply the same DTB overaly which we get from OP-
> TEE on both Linux and uboot.
> 
> For now this can only happen for LS1028 platform, if you want we can do this,
> But it will be incomplete in my opinion as it will not enable all the boards.
> We need to work on them again.
> 
> >
> > >> > We don't use DTB in OP-TEE, but when we use CAAM in OP-TEE,
> > >> > OP-TEE reserves One Job Ring for its use and that is communicated
> > >> > to Kernel using DTB overlay.
> > >> >
> > >> >> what if the overlay doesn't match the dtb?
> > >> > I didn't get this point, can you please elaborate a little.
> > >>
> > >> You are merging a dtb fragment with an unknown dtb, right? Who says
> > >> they match? you might have an old dtb where the supplied dtb
> > >> fragment doesn't make any sense.
> > >>
> > >> I might be missing something here. Eg. where is the linux dtb
> > >> supposed to come from? This patchset is really missing an example
> > >> and a description how things should work.
> > > If supplied DTB does not match with DTB overlay fragment. then
> > > overlay will not get applied.
> >
> > I don't think this is what happens here. fdt_overlay_apply() will mark
> > the fdt as damaged and there will be no fdt at all.
> Ok, got your point, If we have fragment in DTB overlay to modify let's say
> `status` of CAAM job ring, and CAAM job ring node does not exist in the DTB
> on which overlay is going to be applied, In that case the DTB will be marked as
> damaged and it will stop booting of the board, right ?
> But how can we make sure that DTB overlay and DTB on which DTB overlay is
> applied are compatible ?
> Maybe some DTB version check or something like that, when OP-TEE creates
> a DTB overlay, It indicates in the overlay that this can be applied on only DTBs
> with version more than `X`
> 
> 
> > > We don't have any control on where user picks the DTB, but we can only
> > > make sure DTB overlay feature must work with DTBs which are
> upstreamed
> > > If user makes its own customized DTB, we cannot make sure that things
> > > will work.
> >
> > Again. Is there any documentation on how this should all work together?
> > Where does optee get its device tree from? Shouldn't it be the same
> device
> > tree as u-boot and linux? Shouldn't optee modify the device tree in place
> > before jumping back to u-boot?
> Here on LS platforms: Boot Flow is like ATF-> OP-TEE-> ATF->Uboot-> Linux
> 
> Currently for LS platforms, OP-TEE don't use DTBs except for LX2160A.
> And I am talking about the other platforms except LX2160 for now.
> So all peripherals base addresses are currently hardcoded.
> 
> But OP-TEE uses some of the peripherals, and this information needs to
> be passed to following components uboot and linux so that they don't use
> the same peripherals.
> 
> One of the case is CAAM Job Ring. OP-TEE always use CAAM Job Ring 3, and it
> needs to communicate this thing to following components uboot so that they
> don’t
> try to use the same peripherals as used by OP-TEE,
> So, we enabled DTB_OVERLAY option in OP-TEE and will write CAAM Job Ring
> 3 to be
> disabled in that DTB overlay.
> 
> The address where this DTB overlay will be created is passed by ATF which
> ATF will
> pass on to uboot also.
> 
> When control reaches uboot, It  will use that DTB overlay and apply it on
> Linux DTB
> which we passed via tftp on board.
> 
> Currently there is no common DTB which is being used by all the components,
> OP-TEE, Uboot, Linux all are using their own copies of DTB.
> 
> Hope I answered your queries, Please let me know if you need more
> information.
> 
> > Andrey, do you know how this works on imx?
> Actually, I took reference from imx only, They are also just applying DTB
> overlay on linux DTB as of now.
> They are not modifying the uboot DTB according to the DTB overlay.
> 
> 
> Regards,
> Sahil Malhotra