[PATCH v3 09/12] of: property: Simplify of_link_to_phandle()

[Geert Uytterhoeven]

Hi Saravana,

On Wed, Feb 8, 2023 at 3:08 AM Saravana Kannan <saravanak at google.com> wrote:
> On Tue, Feb 7, 2023 at 12:57 PM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> > On Tue, Feb 7, 2023 at 2:42 AM Saravana Kannan <saravanak at google.com> wrote:
> > > The driver core now:
> > > - Has the parent device of a supplier pick up the consumers if the
> > >   supplier never has a device created for it.
> > > - Ignores a supplier if the supplier has no parent device and will never
> > >   be probed by a driver
> > >
> > > And already prevents creating a device link with the consumer as a
> > > supplier of a parent.
> > >
> > > So, we no longer need to find the "compatible" node of the supplier or
> > > do any other checks in of_link_to_phandle(). We simply need to make sure
> > > that the supplier is available in DT.
> > >
> > > Signed-off-by: Saravana Kannan <saravanak at google.com>
> >
> > Thanks for your patch!
> >
> > This patch introduces a regression when dynamically loading DT overlays.
> > Unfortunately this happens when using the out-of-tree OF configfs,
> > which is not supported upstream.  Still, there may be (obscure)
> > in-tree users.
> >
> > When loading a DT overlay[1] to enable an SPI controller, and
> > instantiate a connected SPI EEPROM:
> >
> >     $ overlay add 25lc040
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /keys/status
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/pinctrl-0
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/pinctrl-names
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/cs-gpios
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/status
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /__symbols__/msiof0_pins
> >
> > The SPI controller and the SPI EEPROM are no longer instantiated.
> >
> >     # cat /sys/kernel/debug/devices_deferred
> >     e6e90000.spi    platform: wait for supplier msiof0
> >
> > Let's remove the overlay again:
> >
> >     $ overlay rm 25lc040
> >     input: keys as /devices/platform/keys/input/input1
> >
> > And retry:
> >
> >     $ overlay add 25lc040
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /keys/status
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/pinctrl-0
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/pinctrl-names
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/cs-gpios
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/status
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /__symbols__/msiof0_pins
> >     spi_sh_msiof e6e90000.spi: DMA available
> >     spi_sh_msiof e6e90000.spi: registered master spi0
> >     spi spi0.0: setup mode 0, 8 bits/w, 100000 Hz max --> 0
> >     at25 spi0.0: 512 Byte at25 eeprom, pagesize 16
> >     spi_sh_msiof e6e90000.spi: registered child spi0.0
> >
> > Now it succeeds, and the SPI EEPROM is available, and works.
> >
> > Without this patch, or with this patch reverted after applying the
> > full series:
> >
> >     $ overlay add 25lc040
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /keys/status
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/pinctrl-0
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/pinctrl-names
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/cs-gpios
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /soc/spi at e6e90000/status
> >     OF: overlay: WARNING: memory leak will occur if overlay removed,
> > property: /__symbols__/msiof0_pins
> >     OF: Not linking spi at e6e90000 to interrupt-controller at f1010000 - No
> > struct device
> >     spi_sh_msiof e6e90000.spi: DMA available
> >     spi_sh_msiof e6e90000.spi: registered master spi0
> >     spi spi0.0: setup mode 0, 8 bits/w, 100000 Hz max --> 0
> >     at25 spi0.0: 444 bps (2 bytes in 9 ticks)
> >     at25 spi0.0: 512 Byte at25 eeprom, pagesize 16
> >     spi_sh_msiof e6e90000.spi: registered child spi0.0
> >
> > The SPI EEPROM is available on the first try after boot.
>
> Sigh... I spent way too long trying to figure out if I caused a memory
> leak. I should have scrolled down further! Doesn't look like that part
> is related to anything I did.

Please ignore the memory leak messages.  They are known issues
in the upstream DT overlay code, and not related to your series.

> There are some flags set to avoid re-parsing fwnodes multiple times.
> My guess is that the issue you are seeing has to do with how many of
> the in memory structs are reused vs not when an overlay is
> applied/removed and some of these flags might not be getting cleared
> and this is having a bigger impact with this patch (because the fwnode
> links are no longer anchored on "compatible" nodes).
>
> With/without this patch (let's keep the series) can you look at how
> the following things change between each step you do above (add,
> remove, retry):
> 1) List of directories under /sys/class/devlink
> 2) Enable the debug logs inside __fwnode_link_add(),
> __fwnode_link_del(), device_link_add()

Thanks, I'll give that a try, later...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds