ChanServ changed the topic of #armlinux to: ARM kernel talk [Upstream kernel, find your vendor forums for questions about their kernels] | https://libera.irclog.whitequark.org/armlinux
<marex> rfs613: compatible = "vendor,chip", "spidev"; doesn't work ?
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<marex> rfs613: u-boot has sspi command, it can talk to any SPI device, with or without a driver, it just send a transmission via SPI ... no userspace, no nothing, it is just an u-boot command
<marex> just pick a bus, chipselect, send/receive ...
<marex> rfs613: also, have a look at 'udevadm info /dev/device' , that will tell you the HW path and driver associated with the device , there is zero need for driver-specific compatible strings (=wrong) in the DT
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<Xogium> so… If I have a mcu that lets you map part of its internal or external flash as additional ram, how can I make use of this in linux ? Is there any driver or code that can handle this ? Say I want to take 16 MB off the external qspi flash and use them as ram so I have 32 mb instead of 16 available…
<Xogium> I know I can do this with a rtos, but I wonder if linux can help you do this
<Xogium> heh and before ukleinek gets me I mistyped 32 MB
<Xogium> :D
<Xogium> now… I could be mixing stuff up heh I'm still learning mcu and all of that :)
<ukleinek> Xogium: I guess just setting it up in the bootloader and add an appropriate memory node in dts should do the trick.
<ukleinek> (for 32 mb this isn't worth the effort though :-)
<Xogium> ukleinek: yeah… as long as you don't write in there too often, it could be good…
<Xogium> I mean, I can't even have zram
<Xogium> I'd have used this instead
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<Xogium> zram requires zsmalloc, whatever that exacly is and this requires full MMU. Sorry guys, only have MPU
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<milkylainen> Xogium: Masochistic tendencies? :) I mean. A modern kernel on an MCU with only 16M RAM and then a userspace of sorts? I guess it's possible, but it sounds like a lot of pain.
<milkylainen> I'm guessing some kind of custom Linux, right?
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<Xogium> milkylainen: yeah, definitely custom. Well, made using buildroot
<Xogium> and I've done it mostly as a proof of concept :p show that it was doable, for the most part. I'm just very curious
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<milkylainen> Xogium: Ok. Is it a vanilla kernel that buildroot is using?
<Xogium> milkylainen: yeah, I made all of this on my own actually, there's no config for f769 in br. But yes it is vanilla and didn't require any patching
<Xogium> 5.15.3 kernel
<milkylainen> So vanilla with some sort of tinyconfig?
<milkylainen> I haven't built minimalist stuff in ages. :)
<Xogium> vanilla with stm32_defconfig with a few tweaks, mainly the dram address start / size
<Xogium> kernel's 1.5 MB compressed in gzip
<Xogium> I do wonder if I could make it even smaller
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<Xogium> [ 45.413884] nommu: Allocation of length 724992 from process 65 (getty) failed
<Xogium> oops
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<milkylainen> busybox getty?
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<Xogium> hehe nah kernel
<Xogium> I tried and stuffed a complete busybox in
<Xogium> it did not like that
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<jn> hm? where can i find that implementation of getty?
<Xogium> jn: hah I blinked and was like… What ? And then realized I used the wrong word
<Xogium> I meant to say busybox not kernel
<Xogium> XD
<jn> ah, so that's a yes to milkylainen
<Xogium> no he said barebox
<Xogium> unless I'm going deaf…
<Xogium> oh wait I am
<Xogium> :p
<Xogium> for real I mean
<jn> happens to the best of us :)
<Xogium> yeah
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<milkylainen> busybox getty? under busybox?
<Xogium> milkylainen: sure ? Busybox has a getty
<milkylainen> This is confusing. Yes. That is what I'm saying.
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<milkylainen> "hm? where can i find that implementation of getty?"
<milkylainen> "busybox getty? under busybox?"
<Xogium> oh no that was because I said kernel getty
<Xogium> lol
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<jn> confusion all around
<milkylainen> indeed.
<Xogium> land of confusion
<Xogium> there a way to get rid of this ? XIP start address may cause MPU programming issues
<Xogium> aside from disabling the MPU that is
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<jn> Xogium: as far as i can see, the linker script that prints this warning expects the start address to be aligned to 1 MiB
<jn> ASSERT(!(_xiprom & (SZ_1M - 1)), "XIP start address may cause MPU programming issues")
<jn> ASSERT(!(_exiprom & (SZ_128K - 1)), "XIP end address may cause MPU programming issues")
<jn> so the first step would be to find out where this start address is in your build
<Xogium> jn: hmm this would explain… I am trying to figure out if I need u-boot for this or not…
<Xogium> like could I just burn xipImage on the flash at the correct address
<jn> the warning is already produced by a linux linker script, so it should probably be fixed in linux configuration
<Xogium> no bootloader involved at all, except the ROM ?
<Xogium> I'm trying to get rid of the use for a micro sd card ;)
<Xogium> so I have internal and external flash but I don't know how to XIP to external flash not to mention linux dt probably doesn't have this
<jn> XIP usually requires that the code/data memory (flash) is directly memory-mapped by hardware, and there's no step of loading all that stuff into RAM before execution
<jn> RAM might still be used for writable data
<Xogium> jn: ah, yeah… makes sense. I *think* the stm32f769 has this
<Xogium> memory map for the internal and external flash, that is
<Xogium> I was planning on trying to stuff the whole thing as cramfs
<Xogium> not kernel but at least userspace
<Xogium> I'm sort of following the serie Nocolas Pitre wrote about shrinking the kernel to the best of my ability
<Xogium> erm, Nicolas Pitre that is
<Xogium> so I guess… Like, can I get rid of u-boot and directly boot kernel ?
<Xogium> or should I stick to u-boot in spl mode
<Xogium> with falcon mode
<jn> not necessarily
<jn> there might be some necessary hardware initialization that uboot does
<jn> SPL + kernel might be enough
<Xogium> hmm
<Xogium> well, u-boot spl is 30 kb so that's ok
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<Xogium> 30 KB for spl, 1.7 MB for kernel so far
<Xogium> might get rid of the entire block layer since I don't use usb or don't plan to keep using micro sd
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<Xogium> so all I need to do you say, if I can arbitrarily address the external qspi flash via memory map, is just get some range of it to use as XIP ? Hmm
<Xogium> but what about u-boot, doesn't it need to init said qspi flash ?
<Xogium> like with sf probe or some such
<Xogium> hmm… I treid to put the kernel in the same place that u-boot.bin was previously at in the map… SPL now hangs after trying to boot from XIP
<Xogium> *tried
<Xogium> U-Boot SPL 2021.10 (Nov 20 2021 - 13:08:09 -0500)
<Xogium> Trying to boot from XIP
<Xogium> that's all I get
<Xogium> u-boot.bin binary ran ok with that, but somehow xipImage doesn't
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