On Mon, Aug 24, 2020 at 09:18:40PM +0000, Reuben Dowle wrote: > I can see that arm64 requires 8 bytes. That is stated in section 2 of > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm64/booting.rst. > > I can't see a similar requirement for arm, although my search was not > exhaustive. More generally I can see that all device trees must be at least 4 > byte aligned (from section II.2 of > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/booting-without-of.rst) > > So it does seem that 8 bytes would work for at least both of these. I would > be happy with hard-coding that, as I doubt it would cause any problems with > other architectures. > > I don’t have anything to add on the ability to relocate the device tree. In > my case the device tree is for the next stage u-boot, so won't need > relocating. This might become an issue if this was booting direct to linux > from the SPL perhaps.
For arm it's spelled out differently[1] as "64bit aligned address". So using 8 with a big annotated comment is probably best here. And then ah, yes, that's right, that's why we may end up in the case we're in. Thanks! [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/arm/booting.rst#n126 > > > > ________________________________ > > [cid:4RFLogo(Custom)(2)_0f31a7de-6dd6-43cf-bc6a-a097a2b80b69.jpg] > Reuben Dowle > Software Architect > > Phone: > > Fax: > E-Mail: > Website: > > > +64 4 499 6000 > > +64 4 473 4447 > reuben.do...@4rf.com<mailto:reuben.do...@4rf.com> > Https://www.4rf.com<https://www.4rf.com> > > > ________________________________ > > [cid:Family_53c410b1-7227-4a5f-9acb-f09bd7617a39.png] > <http://www.4rf.com/news/events> > > -----Original Message----- > > From: Tom Rini <tr...@konsulko.com> > > Sent: Tuesday, 25 August 2020 8:40 am > > To: Reuben Dowle <reuben.do...@4rf.com> > > Cc: u-boot@lists.denx.de > > Subject: Re: [PATCH] Fix data abort caused by mis-aligning fit data in > > > > On Mon, Aug 24, 2020 at 08:05:24PM +0000, Reuben Dowle wrote: > > > > > Should I submit a new patch with the alignment set to 8 bytes? I would > > think a hard coded 8 bytes would not be the best solution, since not all > > architectures will need that much alignment. I suspect some would work with > > any alignment, and most 32-bit archs would be fine with 4-byte alignment. > > > > > > Our released software is actually using a patch to align to 4096 bytes, > > > but I > > knew that was unnecessarily large. I was not really sure what would be an > > appropriate value here, and took a guess at ARCH_DMA_MINALIGN when I > > cleaned it up for submitting upstream. Is there a better define to use? > > > > > > I am also interested to know where the 8 byte alignment requirement is > > documented. > > > > So we're talking about the device tree file, and only that, in this part > > of the code, right? In the Linux kernel documentation, both arm and > > arm64 document that the device tree must be on an 8-byte aligned > > address. That is the bare minimum. If we aren't further relocating it > > (as fdt_high is set to 0xffffffff for example, which in general is wrong > > and bad), that's still the best we can do. It would be good to allow > > for further relocation down the line as we aren't making sure it > > wouldn't be overwritten by the kernel BSS, etc. > > > > -- > > Tom > ________________________________ > The information in this email communication (inclusive of attachments) is > confidential to 4RF Limited and the intended recipient(s). If you are not the > intended recipient(s), please note that any use, disclosure, distribution or > copying of this information or any part thereof is strictly prohibited and > that the author accepts no liability for the consequences of any action taken > on the basis of the information provided. If you have received this email in > error, please notify the sender immediately by return email and then delete > all instances of this email from your system. 4RF Limited will not accept > responsibility for any consequences associated with the use of this email > (including, but not limited to, damages sustained as a result of any viruses > and/or any action or lack of action taken in reliance on it). -- Tom
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