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    SubjectRe: nvmem-cells regression after adding 'call of_platform_populate() for MTD partitions'
    On Fri, Dec 16, 2022 at 3:05 AM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
    >
    > Hi Saravana, Maxim, Maxim,
    >
    > saravanak@google.com wrote on Wed, 14 Dec 2022 13:53:54 -0800:
    >
    > > On Tue, Dec 13, 2022 at 8:54 AM Miquel Raynal <miquel.raynal@bootlin.com> wrote:
    > > >
    > > > Hi Maxim,
    > > >
    > > > bigunclemax@gmail.com wrote on Tue, 13 Dec 2022 14:02:34 +0300:
    > > >
    > > > > I looked closer at commit 658c4448bbbf and bcdf0315a61a, 5db1c2dbc04c16 commits.
    > > > > Looks like we have two different features binded to one property - "compatible".
    > > > >
    > > > > From one side it is the ability to forward the subnode of the mtd
    > > > > partition to the nvmem subsystem (658c4448bbbf and ac42c46f983e).
    > > > > And from another side is the ability to use custom initialization of
    > > > > the mtd partition (bcdf0315a61a and 5db1c2dbc04c16).
    > > > >
    > > > > What I mean:
    > > > > According to ac42c46f983e I can create DT like this:
    > > > > - |
    > > > > partitions {
    > > > > compatible = "fixed-partitions";
    > > > > #address-cells = <1>;
    > > > > #size-cells = <1>;
    > > > >
    > > > > partition@0 {
    > > > > compatible = "nvmem-cells";
    > > > > reg = <0x40000 0x10000>;
    > > > > #address-cells = <1>;
    > > > > #size-cells = <1>;
    > > > > macaddr_gmac1: macaddr_gmac1@0 {
    > > > > reg = <0x0 0x6>;
    > > > > };
    > > > > };
    > > > > };
    > > > >
    > > > >
    > > > > And according to 5db1c2dbc04c16 I can create DT like this:
    > > > > - |
    > > > > partitions {
    > > > > compatible = "fixed-partitions";
    > > > > #address-cells = <1>;
    > > > > #size-cells = <1>;
    > > > >
    > > > > partition@0 {
    > > > > compatible = "u-boot,env";
    > > > > reg = <0x40000 0x10000>;
    > > > > };
    > > > > };
    > > > >
    > > > > But I can not use them both, because only one "compatible" property allowed.
    > > > > This will be incorrect:
    > > > > - |
    > > > > partitions {
    > > > > compatible = "fixed-partitions";
    > > > > #address-cells = <1>;
    > > > > #size-cells = <1>;
    > > > >
    > > > > partition@0 {
    > > > > compatible = "u-boot,env"; # from ac42c46f983e
    > > > > compatible = "nvmem-cells"; # from 5db1c2dbc04c
    > > >
    > > > What about:
    > > >
    > > > compatible = "u-boot,env", "nvmem-cells";
    > > >
    > > > instead? that should actually work.
    > > >
    > > > > reg = <0x40000 0x10000>;
    > > > > #address-cells = <1>;
    > > > > #size-cells = <1>;
    > > > > macaddr_gmac1: macaddr_gmac1@0 {
    > > > > reg = <0x0 0x6>;
    > > > > };
    > > > > };
    > > > > };
    > > > >
    > > > > > compatible: Duplicate property name
    > > > >
    > > > > вт, 13 дек. 2022 г. в 12:46, Miquel Raynal <miquel.raynal@bootlin.com>:
    > > > > >
    > > > > > Hi Maxim,
    > > > > >
    > > > > > fido_max@inbox.ru wrote on Mon, 12 Dec 2022 20:57:49 +0300:
    > > > > >
    > > > > > > Hi, Miquel!
    > > > > > >
    > > > > > > On 12.12.2022 19:37, Miquel Raynal wrote:
    > > > > > >
    > > > > > > > Let me try to recap the situation for all the people I just involved:
    > > > > > > >
    > > > > > > > * An Ethernet driver gets its mac address from an nvmem cell. The
    > > > > > > > Ethernet controller DT node then has an "nvmem-cells" property
    > > > > > > > pointing towards an nvmem cell.
    > > > > > > > * The nvmem cell comes from an mtd partition.
    > > > > > > > * The mtd partition is flagged with a particular compatible
    > > > > > > > (which is also named "nvmem-cells") to tell the kernel that the node
    > > > > > > > produces nvmem cells.
    > > > > > > > * The mtd partition itself has no driver, but is the child node of a
    > > > > > > > "partitions" container which has one (in this case,
    > > > > > > > "fixed-partitions", see the snippet below).
    > > > > > > >
    > > > > > > > Because the "nvmem-cells" property of the Ethernet node points at the
    > > > > > > > nvmem-cell node, the core create a device link between the Ethernet
    > > > > > > > controller (consumer) and the mtd partition (producer).
    > > > > > > >
    > > > > > > > The device link in this case will never be satisfied because no driver
    > > > > > > > matches the "nvmem-cells" compatible of the partition node.
    > > > > > > >
    > > > > > > > Reverting commit bcdf0315a61a ("mtd: call of_platform_populate() for MTD
    > > > > > > > partitions") would IMHO not make much sense, the problem comes from the
    > > > > > > > device link side and even there, there is nothing really "wrong",
    > > > > > > > because I really expect the mtd device to be ready before the
    > > > > > > > Ethernet controller probe, the device link is legitimate.
    > > > > > > >
    > > > > > > > So I would like to explore other alternatives. Here are a bunch of
    > > > > > > > ideas, but I'm open:
    > > > > > >
    > > > > > > How about to create simple driver with compatible="nvmem-cell" and to move all the suff from main mtd driver which serves nvmem-cell to the probe function?
    > > > > >
    > > > > > This is probably worth the try but I doubt you can make it work without
    > > > > > regressions because IIRC the nvmem registration happens no matter the
    > > > > > compatible (not mentioning the user-otp and factory-otp cases). You can
    > > > > > definitely try this out if you think you can come up with something
    > > > > > though.
    > > > > >
    > > > > > But I would like to hear from the device-link gurus :) because even if
    > > > > > we fix mtd with a "trick" like above, I guess we'll very likely find
    > > > > > other corner cases like that and I am interested in understanding the
    > > > > > rationale of what could be a proper fix.
    > > > > >
    > >
    > > Responding to the whole thread.
    > >
    > > I'm going by Miquel's first email in which he cc'ed me and haven't
    > > actually looked at the mtd code. Couple of comments:
    > >
    > > Independent of mtd/nvmem-cell, I generally frown on having a
    > > compatible string for a child node that you don't treat as a device.
    > > Even more so if you actually create a struct device for it and then
    > > don't do anything else with it. That's just a waste of memory. So, in
    > > general try to avoid that in the future if you can.
    >
    > Agreed, it didn't triggered any warnings in my head in the first place,
    > sorry about that.
    >
    > > Also, there are flags the parent device's driver can set that'll tell
    > > fw_devlink not to treat a specific DT node as a real device. So, if we
    > > really need that I'll dig up and suggest a fix.
    >
    > Interesting, that would indeed very likely fix it.
    >
    > > Lastly and more importantly, I've a series[1] that stops depending on
    > > the compatible property for fw_devlink to work. So it should be
    > > smarter than it is today. But that series has known bugs for which I
    > > gave test fixes in that thread. I plan to make a v2 of that series
    > > with that fix and I'm expecting it'll fix a bunch of fw_devlink
    > > issues.
    > >
    > > Feel free to give v1 + squashing the fixes a shot if you are excited
    > > to try it. Otherwise, I'll try my best to get around to it this week
    > > (kinda swamped though + holidays coming up, so no promises).
    >
    > Can you please include us in your next submission?
    > * Maxim Kiselev <bigunclemax@gmail.com>
    > * Maxim Kochetkov <fido_max@inbox.ru>
    > * Miquel Raynal <miquel.raynal@bootlin.com>

    Will do.

    -Saravana

    >
    > > [1] - https://lore.kernel.org/lkml/20220810060040.321697-1-saravanak@google.com/
    >
    > Maxim, any chance you give this a try?
    >
    > Thanks,
    > Miquèl

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