On Wed, May 8, 2024 at 7:19 PM Elliot Berman <quic_eberman(a)quicinc.com> wrote:
>
> On Thu, May 02, 2024 at 09:00:47AM -0500, Rob Herring wrote:
> > On Wed, May 1, 2024 at 4:18 PM Humphreys, Jonathan <j-humphreys(a)ti.com> wrote:
> > > [1] Rather than using the device tree source filename, to have more flexibility,
> > > one can conceive an ID or compatible string that the OS could then scan the DTBs
> > > to find a match.
> >
> > I agree with Daniel that we should use the root node compatible for
> > this. We discussed this a while back on this list (or u-boot?). To
> > summarize, both using the filename or root node compatible were
> > proposed. Several folks (myself included) don't like making the
> > filename an ABI. However, there are some cases where the filename is
> > more unique than the root node compatible. We should fix those root
> > node compatibles in that case IMO.
>
> I think firmware-provided compatible string can cause headaches for both
> firmware and OS developers. I gave a talk about this at EOSS [1,2] and
> we've been posting some proposals [3,4] to introduce a board-id, which
> allows DTBs to have varying degrees of precision about describing what
> hardware they are applicable to.
>
> Compatible strings should be a mapping of some identifier
> registers/storage into a string. Today, bootloader has to figure out
> that mapping and I understood Jon's proposal as wanting to get firmware
> to provide the compatible string. However, the compatible string for a
> DTB could need to describe only a subset of those identifiers
> (compatible string) to get a DTB that works. This would be especially
> true for DT overlays, although there are other real and hypothetical
> situations where a DTB shouldn't/can't describe the complete set of
> identifiers. Firmware either needs to provide every possible combination
> of compatible string or knowledge needs to be baked into the OS about
> interpreting the compatible string. In simple terms, the proposal is to
> split out the identifers that are baked into the compatible string into
> separate "board-id" properties.
I don't think there is any way the OS (or OS loader) would be able
handle these properties and the logic to parse them. It all looks to
be platform specific. This could only work if the OS says to the
firmware "here's the 1000 DTB files, which one should I use? That's
quite different from the current proposals of how this would work.
Rob
On Tue, Mar 26, 2024 at 4:29 PM Daniel Golle <daniel(a)makrotopia.org> wrote:
>
> Hi Rob,
>
> On Tue, Mar 26, 2024 at 03:24:49PM -0500, Rob Herring wrote:
> > +boot-architecture list
>
> Good idea, thank you :)
Now really adding it. :(
Will reply to rest later.
> >
> > On Mon, Mar 25, 2024 at 03:38:19PM +0000, Daniel Golle wrote:
> > > On Mon, Mar 25, 2024 at 10:10:46AM -0500, Rob Herring wrote:
> > > > On Thu, Mar 21, 2024 at 07:31:48PM +0000, Daniel Golle wrote:
> > > > > On embedded devices using an eMMC it is common that one or more (hw/sw)
> > > > > partitions on the eMMC are used to store MAC addresses and Wi-Fi
> > > > > calibration EEPROM data.
> > > > >
> > > > > Implement an NVMEM provider backed by a block device as typically the
> > > > > NVMEM framework is used to have kernel drivers read and use binary data
> > > > > from EEPROMs, efuses, flash memory (MTD), ...
> > > > >
> > > > > In order to be able to reference hardware partitions on an eMMC, add code
> > > > > to bind each hardware partition to a specific firmware subnode.
> > > > >
> > > > > Overall, this enables uniform handling across practially all flash
> > > > > storage types used for this purpose (MTD, UBI, and now also MMC).
> > > > >
> > > > > As part of this series it was necessary to define a device tree schema
> > > > > for block devices and partitions on them, which (similar to how it now
> > > > > works also for UBI volumes) can be matched by one or more properties.
> > > > >
> > > > > ---
> > > > > This series has previously been submitted as RFC on July 19th 2023[1]
> > > > > and most of the basic idea did not change since. Another round of RFC
> > > > > was submitted on March 5th 2024[2] which has received overall positive
> > > > > feedback and only minor corrections have been done since (see
> > > > > changelog below).
> > > >
> > > > I don't recall giving positive feedback.
> > > >
> > > > I still think this should use offsets rather than partition specific
> > > > information. Not wanting to have to update the offsets if they change is
> > > > not reason enough to not use them.
> > >
> > > Using raw offsets on the block device (rather than the partition)
> > > won't work for most existing devices and boot firmware out there. They
> > > always reference the partition, usually by the name of a GPT
> > > partition (but sometimes also PARTUUID or even PARTNO) which is then
> > > used in the exact same way as an MTD partition or UBI volume would be
> > > on devices with NOR or NAND flash.
> >
> > MTD normally uses offsets hence why I'd like some alignment. UBI is
> > special because raw NAND is, well, special.
>
> I get the point and in a way this is also already intended and
> supported by this series. You can already just add an 'nvmem-layout'
> node directly to a disk device rather than to a partition and define a
> layout in this way.
>
> Making this useful in practice will require some improvements to the
> nvmem system in Linux though, because that currently uses signed 32-bit
> integers as addresses which is not sufficient for the size of the
> user-part of an eMMC. However, that needs to be done then and should
> of course not be read as an excuse.
>
> >
> > > Just on eMMC we usually use a GPT
> > > or MBR partition table rather than defining partitions in DT or cmdline,
> > > which is rather rare (for historic reasons, I suppose, but it is what it
> > > is now).
> >
> > Yes, I understand how eMMC works. I don't understand why if you have
> > part #, uuid, or name you can't get to the offset or vice-versa. You
> > need only 1 piece of identification to map partition table entries to DT
> > nodes.
>
> Yes, either of them (or a combination) is fine. In practise I've mostly
> seen PARTNAME as identifier used in userland scripts, and only adding
> this for now will probably cover most devices (and existing boot firmware)
> out there. Notable exceptions are devices which are using MBR partitions
> because the BootROM expects the bootloader to be at the same block as
> we would usually have the primary GPT. In this case we can only use the
> PARTNO, of course, and it stinks.
> MediaTek's MT7623A/N is such an example, but it's a slingly outdated
> and pretty weird niche SoC I admit.
>
> > Sure, offsets can change, but surely the firmware can handle
> > adjusting the DT?
>
> Future firmware may be able to do this, of course. Current existing
> firmware already out there on devices such as the quite popular
> GL.iNet MT-6000, Netgear's Orbi and Orbi Pro series as well as all
> Adtran SmartRG devices does not. Updating or changing the boot
> firmware of devices already out there is not intended and quite
> challenging, and will make the device incompatible with its vendor
> firmware. Hence it would be better to support replacing only the
> Linux-based firmware (eg. with OpenWrt or even Debian or any
> general-purpose Linux, the eMMC is large enough...) while not having
> to touch the boot firmware (and risking to brick the device if that
> goes wrong).
>
> Personally, I'm rather burdened and unhappy with vendor attempts to
> have the boot firmware mess around too much in (highly customized,
> downstream) DT, it may look like a good solution at the moment, but
> can totally become an obstacle in an unpredictable future (no offense
> ASUS...)
>
> >
> > An offset would also work for the case of random firmware data on the
> > disk that may or may not have a partition associated with it. There are
> > certainly cases of that. I don't think we have much of a solution for
> > that other than trying to educate vendors to not do that or OS
> > installers only supporting installing to something other than eMMC. This
> > is something EBBR[1] is trying to address.
>
> Absolutely. Actually *early* GL-iNet devices did exactly that: Use the
> eMMC boot hw-partitions to store boot firmware as well as MAC
> addresses and potentially also Wi-Fi calibration data.
>
> The MT-2500 is the example I'm aware of and got sitting on my desk for
> testing with this very series (which allows to also reference eMMC
> hardware partitions, see "[7/8] mmc: block: set fwnode of disk
> devices").
> Unfortunately later devices such the the flag-ship MT-6000 moved MAC
> addresses and WiFi-EEPROMs into a GPT partition on the user-part of
> the eMMC.
>
> >
> > > Depending on the eMMC chip used, that partition may not even be at the
> > > same offset for different batches of the same device and hence I'd
> > > like to just do it in the same way vendor firmware does it as well.
> >
> > Often vendor firmware is not a model to follow...
>
> I totally agree. However, I don't see a good reason for not supporting
> those network-appliance-type embedded devices which even ship with
> (outdated, downstream) Linux by default while going through great
> lengths for things like broken ACPI tables in many laptops which
> require lots of work-arounds to have features like suspend-to-disk
> working, or even be able to run Linux at all.
>
> >
> > > Chad of Adtran has previously confirmed that [1], which was the
> > > positive feedback I was refering to. Other vendors like GL-iNet or
> > > Netgear are doing the exact same thing.
> > >
> > > As of now, we support this in OpenWrt by adding a lot of
> > > board-specific knowledge to userland, which is ugly and also prevents
> > > using things like PXE-initiated nfsroot on those devices.
> > >
> > > The purpose of this series is to be able to properly support such devices
> > > (ie. practially all consumer-grade routers out there using an eMMC for
> > > storing firmware).
> > >
> > > Also, those devices have enough resources to run a general purpose
> > > distribution like Debian instead of OpenWrt, and all the userland
> > > hacks to set MAC addresses and extract WiFi-EEPROM-data in a
> > > board-specific ways will most certainly never find their way into
> > > Debian. It's just not how embedded Linux works, unless you are looking
> > > only at the RaspberryPi which got that data stored in a textfile
> > > which is shipped by the distribution -- something very weird and very
> > > different from literally all of-the-shelf routers, access-points or
> > > switches I have ever seen (and I've seen many). Maybe Felix who has
> > > seen even more of them can tell us more about that.
> >
> > General purpose distros want to partition the disk themselves. Adding
> > anything to the DT for disk partitions would require the installer to be
> > aware of it. There's various distro folks on the boot-arch list, so
> > maybe one of them can comment.
>
> Usually the installers are already aware to not touch partitions when
> unaware of their purpose. Repartitioning the disk from scratch is not
> what (modern) distributions are doing, at least the EFI System
> partition is kept, as well as typical rescue/recovery partitions many
> vendors put on their (Windows, Mac) laptops to allow to "factory
> reset" them.
>
> Installers usually offer to replace (or resize) the "large" partition
> used by the currently installed OS instead.
>
> And well, the DT reference to a partition holding e.g. MAC addresses
> does make the installer aware of it, obviously.
>
>
> Thank you for the constructive debate!
>
>
> Cheers
>
>
> Daniel
>
>
> >
> > Rob
> >
> > [1] https://arm-software.github.io/ebbr/index.html#document-chapter4-firmware-m…
