Re: [PATCH RFC v3 1/8] of: Mark interconnects property supplier as optional

Saravana Kannan
2022-07-27T18:59:41Z

On Wed, Jul 27, 2022 at 10:17 AM Paul Kocialkowski
<paul.kocialkowski@bootlin.com> wrote:
>
> Hi,
>
> On Wed 27 Jul 22, 09:06, Saravana Kannan wrote:
> > On Wed, Jul 27, 2022 at 5:06 AM Maxime Ripard <maxime@cerno.tech> wrote:
> > >
> > > Hi,
> > >
> > > On Mon, Mar 07, 2022 at 07:34:22PM -0800, Saravana Kannan wrote:
> > > > On Mon, Mar 7, 2022 at 3:21 PM Rob Herring <robh@kernel.org> wrote:
> > > > >
> > > > > +Saravana
> > > > >
> > > > > On Wed, Mar 02, 2022 at 10:10:53PM +0100, Paul Kocialkowski wrote:
> > > > > > In order to set their correct DMA address offset, some devices rely on
> > > > > > the device-tree interconnects property which identifies an
> > > > > > interconnect node that provides a dma-ranges property that can be used
> > > > > > to set said offset.
> > > > > >
> > > > > > Since that logic is all handled by the generic openfirmware and driver
> > > > > > code, the device-tree description could be enough to properly set
> > > > > > the offset.
> > > > > >
> > > > > > However the interconnects property is currently not marked as
> > > > > > optional, which implies that a driver for the corresponding node
> > > > > > must be loaded as a requirement. When no such driver exists, this
> > > > > > results in an endless EPROBE_DEFER which gets propagated to the
> > > > > > calling driver. This ends up in the driver never loading.
> > > > > >
> > > > > > Marking the interconnects property as optional makes it possible
> > > > > > to load the driver in that situation, since the EPROBE_DEFER return
> > > > > > code will no longer be propagated to the driver.
> > > > > >
> > > > > > There might however be undesirable consequences with this change,
> > > > > > which I do not fully grasp at this point.
> > > >
> > > > Temporary NACK till I get a bit more time to take a closer look. I
> > > > really don't like the idea of making interconnects optional. IOMMUs
> > > > and DMAs were exceptions. Also, we kinda discuss similar issues in
> > > > LPC. We had some consensus on how to handle these and I noted them all
> > > > down with a lot of details -- let me go take a look at those notes
> > > > again and see if I can send a more generic patch.
> > > >
> > > > Paul,
> > > >
> > > > Can you point to the DTS (not DTSI) file that corresponds to this?
> > > > Also, if it's a builtin kernel, I'd recommend setting
> > > > deferred_probe_timeout=1 and that should take care of it too.
> > >
> > > For the record, I also encountered this today on next-20220726 with this
> > > device:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/sun5i.dtsi#n775
> > >
> > > The driver won't probe without fw_devlink=off
> >
> > Really? I basically ended up doing what I mentioned in my original
> > reply. next-20220726 should have my changes that'll make sure
> > fw_devlink doesn't block any probe (it'll still try to create as many
> > device links as possible) after 10s (default deferred probe timeout).
> > Can you try to find more info on why it's not probing?
> > <debugfs>/devices_deferred should give more details.
>
> By the way last time I checked the initial issue that I reported appeared to be
> fixed by the patch (Extend deferred probe timeout on driver registration).

Thanks for the confirmation.

-Saravana