Hi Alex, > -----Original Message----- > From: Alexander Graf [mailto:ag...@suse.de] > Sent: Thursday, June 29, 2017 7:34 PM > To: Siva Durga Prasad Paladugu <siva...@xilinx.com>; Michal Simek > <michal.si...@xilinx.com> > Cc: u-boot@lists.denx.de; Tom Rini <tr...@konsulko.com>; Simon Glass > <s...@chromium.org> > Subject: Re: [U-Boot] [PATCH] arch: armv8: Remove the error when dcache is > off > > > > On 29.06.17 15:44, Siva Durga Prasad Paladugu wrote: > > Hi, > > > >> -----Original Message----- > >> From: Alexander Graf [mailto:ag...@suse.de] > >> Sent: Tuesday, June 27, 2017 6:08 PM > >> To: Michal Simek <michal.si...@xilinx.com> > >> Cc: Siva Durga Prasad Paladugu <siva...@xilinx.com>; > >> u-boot@lists.denx.de; Tom Rini <tr...@konsulko.com>; Simon Glass > >> <s...@chromium.org>; Siva Durga Prasad Paladugu <siva...@xilinx.com> > >> Subject: Re: [U-Boot] [PATCH] arch: armv8: Remove the error when > >> dcache is off > >> > >> > >> > >>> Am 27.06.2017 um 13:52 schrieb Michal Simek > <michal.si...@xilinx.com>: > >>> > >>>> On 27.6.2017 13:46, Alexander Graf wrote: > >>>> > >>>> > >>>>> On 27.06.17 13:20, Michal Simek wrote: > >>>>> Hi, > >>>>> > >>>>>> On 27.6.2017 13:01, Alexander Graf wrote: > >>>>>> I don't think that's going to work - at least not without > >>>>>> compiler flag changes. By default, gcc will happily generate > >>>>>> unaligned accesses. If you disable dcache, these will trap. > >>>>> > >>>>> What's that compiler flags we should be using to avoid that? > >>>> > >>>> It's a combination of > >>>> > >>>> -mstrict-align > >>>> > >>>> plus crossing fingers with lots of praying plus making sure that > >>>> every code you call also follows -mstrict-align plus > >>>> double-checking that you don't break the kernel booting ABI: > >>>> > >>>> > >>>> http://elixir.free-electrons.com/linux/v4.12-rc7/source/Documentati > >>>> on > >>>> /arm64/booting.txt > >>>> > >>>> > >>>> In the booti case, disabling dcache seems to be legitimate. In the > >>>> bootefi case however, it's not. > >>> > >>> Non wants to boot the kernel. It is really about programming stuff. > >>> > >>>> > >>>> So you will also need to set CONFIG_EFI_LOADER to depend on > >>>> !CONFIG_SYS_DCACHE_OFF which means you will want to convert > >>>> CONFIG_SYS_DCACHE_OFF to Kconfig first :). > >>> > >>> ok. I will let Siva to do it just wanted to refresh this topic. > >>> > >>> > >>>>> The reason for this change is to have really small u-boot which > >>>>> fits to OCM without DDR to be able to do initial programming. > >>>> > >>>> Yup, makes sense. I'm just slightly scared by the idea :). > > > > I can see that, we are anyway avoiding that error message for SPL > > BUILD where dcache is off. > > Also, dcache will be ON by default, until and unless user disable it > > through CONFIG_SYS_DCACHE_OFF. > > > > -mstrict-align is already used for armv8 in > > arch/arm/cpu/armv8/config.mk > > > > Finally I feel, we can remove this check or atleast we should make it as > #warning instead of #error. > > I put it in because UEFI binaries can assume that unaligned instructions > work. So please at least convert CONFIG_SYS_DCACHE_OFF to Kconfig and > make it mutually exclusive to CONFIG_EFI_LOADER.
I got your point but, Iam bit concerned to do this change as it may break for someone if they are using both DCACHE_OFF and EFI_LOADER, Isn't it? I don’t have idea on UEFI side, all assume unaligned instructions work or it is configurable when building? Thanks, Siva > > > Alex _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
