On Tue, 12 Mar 2024 at 13:30, Daniel Golle <daniel@xxxxxxxxxxxxxx> wrote: > > Hi Ulf, > > On Tue, Mar 12, 2024 at 01:22:49PM +0100, Ulf Hansson wrote: > > On Tue, 5 Mar 2024 at 21:23, Daniel Golle <daniel@xxxxxxxxxxxxxx> 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 block devices 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. > > > > > > This series is meant to open the discussion on how exactly the device > > > tree schema for block devices and partitions may look like, and even > > > if using the block layer to back the NVMEM device is at all the way to > > > go -- to me it seemed to be a good solution because it will be reuable > > > e.g. for (normal, software GPT or MBR) partitions of an NVMe SSD. > > > > > > This series has previously been submitted on July 19th 2023[1] and most of > > > the basic idea did not change since. > > > > > > However, the recent introduction of bdev_file_open_by_dev() allow to > > > get rid of most use of block layer internals which supposedly was the > > > main objection raised by Christoph Hellwig back then. > > > > > > Most of the other comments received for in the first RFC have also > > > been addressed, however, what remains is the use of class_interface > > > (lacking an alternative way to get notifications about addition or > > > removal of block devices from the system). As this has been criticized > > > in the past I'm specifically interested in suggestions on how to solve > > > this in another way -- ideally without having to implement a whole new > > > way for in-kernel notifications of appearing or disappearing block > > > devices... > > > > > > And, in a way just like in case of MTD and UBI, I believe acting as an > > > NVMEM provider *is* a functionality which belongs to the block layer > > > itself and, other than e.g. filesystems, is inconvenient to implement > > > elsewhere. > > > > I don't object to the above, however to keep things scalable at the > > block device driver level, such as the MMC subsystem, I think we > > should avoid having *any* knowledge about the binary format at these > > kinds of lower levels. > > > > Even if most of the NVMEM format is managed elsewhere, the support for > > NVMEM partitions seems to be dealt with from the MMC subsystem too. > > In an earlier iteration of this RFC it was requested to make NVMEM > support opt-in (instead of opt-out for mtdblock and ubiblock, which > already got their own NVMEM provider implementation). > Hence at least a change to opt-in for NVMEM support is required in the > MMC subsystem, together with making sure that MMC devices have their > fwnode assigned. So, the NVMEM support needs to be turned on (opt-in) for each and every block device driver? It's not a big deal for me - and I would be happy to apply such a change. On the other hand, it is just some binary data that is stored on the flash, why should MMC have to opt-in or opt-out at all? It should be the upper layers who decide what to store on the flash, not the MMC subsystem, if you get my point. > > > Why can't NVMEM partitions be managed the usual way via the MBR/GPT? > > Absolutely, maybe my wording was not clear, but that's exactly what > I'm suggesting here. There are no added parsers nor any knowledge > about binary formats in this patchset. Right, but there are new DT bindings added in the $subject series that allows us to describe NVMEM partitions for an eMMC. Why isn't that parsed from the MBR/GPT, etc, rather than encoded in DT? > > Or did I misunderstand your comment? Maybe. I am just trying to understand this, so apologize if you find my questions silly. :-) Kind regards Uffe
