Hi Michael, -----Original Message----- From: Michael Walle <mich...@walle.cc> Sent: Monday, November 29, 2021 11:17 PM To: Sahil Malhotra (OSS) <sahil.malho...@oss.nxp.com> Cc: Clément Faure <clement.fa...@nxp.com>; Gaurav Jain <gaurav.j...@nxp.com>; Pankaj Gupta <pankaj.gu...@nxp.com>; Priyanka Jain <priyanka.j...@nxp.com>; u-boot@lists.denx.de; Varun Sethi <v.se...@nxp.com>; Ye Li <ye...@nxp.com>; ZHIZHIKIN Andrey <andrey.zhizhi...@leica-geosystems.com> Subject: Re: [PATCH 1/2] fsl-layerscape: add dtb overlay feature
Hi Sahil, Am 2021-11-29 12:55, schrieb Sahil Malhotra (OSS): > Am 2021-11-17 19:11, schrieb Sahil Malhotra (OSS): >>> Could you please add some description what this is doing and for >>> what this is intended? To have a "DTB overlay feature", it is enough >>> to just enable CONFIG_OF_LIBFDT_OVERLAY. >> I will add some description, and yes for DTB overlay feature, it is >> enough to enable CONFIG_OF_LIBFDT_OVERLAY but we need to do this step >> before booting the kernel that's why also have to enable >> CONFIG_OF_SYSTEM_SETUP. > >> Ok. What will the overlay do? Could you give an example? > This overlay will be disabling the crypto nodes which will be used by > optee in secure world, so that linux should not use it. > > >>> Apparently you're adding an overlay passed by optee. Doesn't this >>> have to be applied to u-boot's control dtb too? >> Yes, we will be applying the overlay passed by optee, yes it will be >> applied to dtb which will be passed to uboot for kernel booting. > >> If I read this patch correctly, you're modifying the DT before you >> jump to linux. But I was asking whether you also have to modify the >> DT which is used by u-boot. Eg. if you disable some kind of crypto >> nodes (because optee will use them in secure world), this also have >> to communicated to u-boot, not only linux, no? > Yes, I got your point now, and is very valid, but as of now for u-boot > we are just using the first available node for communicating with CAAM > leaving other job rings as it is. > So we need not to apply overlay to DTB used by uboot. > But we should do the correct thing, so that u-boot and linux doesn't see a > different version of the device tree. > Also what do you mean with "the first available node"? > There is already a new CAAM driver for u-boot pending, see > https://lore.kernel.org/u-boot/20211115070014.17586-1-gaurav.j...@nxp.com/ Very first CAAM Job Ring is always used by u-boot, OP-TEE does not use this job ring. Same job ring can be used by Linux once it boots up. Regards, Sahil Malhotra
