Message-ID: <CAL_JsqKkr6Nnfwa5HevMhqmgsHDXvXMzMFSzw8tiu6Zwe353dg@mail.gmail.com>
Date: Wed, 27 Mar 2024 07:33:51 -0500
From: Rob Herring <robh@...nel.org>
To: Daniel Golle <daniel@...rotopia.org>, 
	Architecture Mailman List <boot-architecture@...ts.linaro.org>
Cc: Diping Zhang <diping.zhang@...inet.com>, Jianhui Zhao <zhaojh329@...il.com>, 
	Jieying Zeng <jieying.zeng@...inet.com>, Chad Monroe <chad.monroe@...ran.com>, 
	Adam Fox <adam.fox@...ran.com>, John Crispin <john@...ozen.org>, Felix Fietkau <nbd@....name>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Ulf Hansson <ulf.hansson@...aro.org>, Jens Axboe <axboe@...nel.dk>, 
	Dave Chinner <dchinner@...hat.com>, Jan Kara <jack@...e.cz>, 
	Thomas Weißschuh <linux@...ssschuh.net>, 
	Damien Le Moal <dlemoal@...nel.org>, Li Lingfeng <lilingfeng3@...wei.com>, 
	Christian Brauner <brauner@...nel.org>, Christian Heusel <christian@...sel.eu>, Min Li <min15.li@...sung.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, Avri Altman <avri.altman@....com>, 
	Hannes Reinecke <hare@...e.de>, Christian Loehle <CLoehle@...erstone.com>, Bean Huo <beanhuo@...ron.com>, 
	Yeqi Fu <asuk4.q@...il.com>, Victor Shih <victor.shih@...esyslogic.com.tw>, 
	Christophe JAILLET <christophe.jaillet@...adoo.fr>, 
	Dominique Martinet <dominique.martinet@...ark-techno.com>, 
	"Ricardo B. Marliere" <ricardo@...liere.net>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org, 
	linux-block@...r.kernel.org
Subject: Re: [PATCH 0/8] block: implement NVMEM provider

On Tue, Mar 26, 2024 at 4:29 PM Daniel Golle <daniel@...rotopia.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-media

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