On Mon, Feb 05, 2018 at 05:11:30PM +0100, Thierry Reding wrote:
> On Wed, Apr 05, 2017 at 02:04:31PM +0200, Thierry Reding wrote:
> > On Wed, Apr 05, 2017 at 10:52:32AM +0200, Lucas Stach wrote:
> > > Hi Rob,
> > >
> > > Am Mittwoch, den 29.03.2017, 08:56 -0500 schrieb Rob Herring:
> > > > On Mon, Jan 23, 2017 at 10:33 AM, Thierry Reding
> > > > <thierry.reding@xxxxxxxxx> wrote:
> > > > > On Fri, Jan 13, 2017 at 06:36:30PM +0100, Lucas Stach wrote:
> > > > >> The i2c adapter on DP AUX is purely a software construct. Linking
> > > > >> it to the device node of the parent device is wrong, as it leads to
> > > > >> 2 devices sharing the same device node, which is bad practice, as
> > > > >
> > > > > Who says that two devices can't share the same device node? It's done
> > > > > all the time.
> > > >
> > > > It's done *some of the time* and I would not consider it best practice.
> > > >
> > > > >> well as the i2c trying to populate children of the i2c adapter by
> > > > >> looking at the child device nodes of the parent device.
> > > > >
> > > > > A set of patches landed in v4.9 to work around this issue in a better
> > > > > way. See:
> > > > >
> > > > > 98b00488459e dt-bindings: i2c: Add support for 'i2c-bus' subnode
> > > > > 7e4c224abfe8 i2c: core: Add support for 'i2c-bus' subnode
> > > >
> > > > What does this buy us? I don't see why this needs to be in DT either.
> > > > Contrary to popular belief, DT is not the only way to instantiate
> > > > devices, C code can still do it.
> > > >
> > > > Also, if this one line removal has no side effects, then how was it
> > > > even needed? We can always add it back if there's some argument for
> > > > why it is needed.
> > >
> > > Okay, so I take this as you mostly agreeing with the rationale of this
> > > patch.
> >
> > For some general background on this: I was originally using this for DP
> > support on Tegra (though that ended up never getting merged because of a
> > particularily frustrating episode of trying to get better link training
> > support into the core helpers) and use it as a means to obtain the I2C
> > controller used for DDC. On Tegra, and I suspect other devices as well,
> > the DP AUX controller is separate from the encoder, so the idea was to
> > link them together using a standard ddc-i2c-bus phandle.
> >
> > I ended up not needing that because the encoder and DP AUX controller
> > are so tightly linked on Tegra that I need direct access to the DP AUX
> > anyway and can therefore directly get the I2C controller from that.
> >
> > If there aren't any other users of this, I suppose we could simply
> > remove the line. Should someone turn up in the future and require the
> > I2C controller to be looked up from a phandle we could add it again,
> > at which point we'd have to investigate again how to get rid of the
> > errors.
> >
> > Acked-by: Thierry Reding <treding@xxxxxxxxxx>
>
> I'm going to have to retract that: I just noticed that this patch breaks
> eDP for Venice2 (and presumably all Tegra124 Nyan boards as well, though
> I don't have those to test with).
>
> My description above isn't quite correct. For eDP device we do use the
> ddc-i2c-bus property in DT to denote which I2C bus to use for probing
> the EDID. So the reason why eDP now breaks is because the simple-panel
> driver will look for the I2C adapter, not find a matching one and defer
> probe (indefinitely).
>
> A, perhaps nicer, alternative I found to make it work is the below
> patch. Would that be more reasonable? Looping in Wolfram.
>
> Thierry
> --- >8 ---
> diff --git a/drivers/i2c/i2c-core-of.c b/drivers/i2c/i2c-core-of.c
> index 8d474bb1dc15..f88527a61cd1 100644
> --- a/drivers/i2c/i2c-core-of.c
> +++ b/drivers/i2c/i2c-core-of.c
> @@ -118,6 +118,14 @@ static int of_dev_node_match(struct device *dev, void *data)
> return dev->of_node == data;
> }
>
> +static int of_parent_node_match(struct device *dev, void *data)
> +{
> + if (dev->parent)
> + return dev->parent->of_node == data;
> +
> + return 0;
> +}
> +
> /* must call put_device() when done with returned i2c_client device */
> struct i2c_client *of_find_i2c_device_by_node(struct device_node *node)
> {
> @@ -143,6 +151,9 @@ struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node)
> struct i2c_adapter *adapter;
>
> dev = bus_find_device(&i2c_bus_type, NULL, node, of_dev_node_match);
> + if (!dev)
> + dev = bus_find_device(&i2c_bus_type, NULL, node, of_parent_node_match);
> +
> if (!dev)
> return NULL;
>
I'd like to point out that a lot of I2C bus drivers actually do the same
thing as the DRM AUX helpers used to do:
$ git grep -n 'dev.of_node.*=' -- drivers/i2c/busses/
drivers/i2c/busses/i2c-altera.c:467: idev->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-aspeed.c:882: bus->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-at91.c:1120: dev->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-axxia.c:561: idev->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-bcm-iproc.c:489: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-bcm-kona.c:858: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-bcm2835.c:367: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-brcmstb.c:664: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-cadence.c:912: id->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-cbus-gpio.c:248: adapter->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-cpm.c:654: cpm->adap.dev.of_node = of_node_get(ofdev->dev.of_node);
drivers/i2c/busses/i2c-cros-ec-tunnel.c:280: bus->adap.dev.of_node = np;
drivers/i2c/busses/i2c-davinci.c:864: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-designware-platdrv.c:351: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-digicolor.c:337: i2c->adap.dev.of_node = np;
drivers/i2c/busses/i2c-dln2.c:215: dln2->adapter.dev.of_node = dev->of_node;
drivers/i2c/busses/i2c-efm32.c:332: ddata->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-eg20t.c:791: pch_adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-emev2.c:387: priv->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-exynos5.c:743: i2c->adap.dev.of_node = np;
drivers/i2c/busses/i2c-gpio.c:322: adap->dev.of_node = np;
drivers/i2c/busses/i2c-hix5hd2.c:456: priv->adap.dev.of_node = np;
drivers/i2c/busses/i2c-ibm_iic.c:748: adap->dev.of_node = of_node_get(np);
drivers/i2c/busses/i2c-img-scb.c:1383: i2c->adap.dev.of_node = node;
drivers/i2c/busses/i2c-imx-lpi2c.c:583: lpi2c_imx->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-imx.c:1086: i2c_imx->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-jz4780.c:751: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-lpc2k.c:432: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-meson.c:423: i2c->adap.dev.of_node = np;
drivers/i2c/busses/i2c-mpc.c:742: i2c->adap.dev.of_node = of_node_get(op->dev.of_node);
drivers/i2c/busses/i2c-mt65xx.c:769: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-mv64xxx.c:935: drv_data->adapter.dev.of_node = pd->dev.of_node;
drivers/i2c/busses/i2c-mxs.c:867: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-nomadik.c:1033: adap->dev.of_node = np;
drivers/i2c/busses/i2c-ocores.c:493: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-octeon-platdrv.c:244: i2c->adap.dev.of_node = node;
drivers/i2c/busses/i2c-omap.c:1457: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-opal.c:236: adapter->dev.of_node = of_node_get(pdev->dev.of_node);
drivers/i2c/busses/i2c-pca-platform.c:174: i2c->adap.dev.of_node = np;
drivers/i2c/busses/i2c-pnx.c:643: alg_data->adapter.dev.of_node = of_node_get(pdev->dev.of_node);
drivers/i2c/busses/i2c-powermac.c:435: adapter->dev.of_node = NULL;
drivers/i2c/busses/i2c-powermac.c:447: adapter->dev.of_node = dev->dev.of_node;
drivers/i2c/busses/i2c-pxa-pci.c:80: pdev->dev.of_node = child;
drivers/i2c/busses/i2c-pxa.c:1313: i2c->adap.dev.of_node = dev->dev.of_node;
drivers/i2c/busses/i2c-qup.c:1608: qup->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-rcar.c:902: adap->dev.of_node = dev->of_node;
drivers/i2c/busses/i2c-riic.c:440: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-rk3x.c:1220: i2c->adap.dev.of_node = np;
drivers/i2c/busses/i2c-s3c2410.c:1210: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-sh_mobile.c:942: adap->dev.of_node = dev->dev.of_node;
drivers/i2c/busses/i2c-sirf.c:335: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-sprd.c:516: i2c_dev->adap.dev.of_node = dev->of_node;
drivers/i2c/busses/i2c-st.c:871: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-stm32f4.c:843: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-stm32f7.c:918: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-stu300.c:918: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-sun6i-p2wi.c:278: p2wi->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-tegra-bpmp.c:311: i2c->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-tegra.c:1006: i2c_dev->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-thunderx-pcidrv.c:210: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-uniphier-f.c:538: priv->adap.dev.of_node = dev->of_node;
drivers/i2c/busses/i2c-uniphier.c:385: priv->adap.dev.of_node = dev->of_node;
drivers/i2c/busses/i2c-versatile.c:88: i2c->adap.dev.of_node = dev->dev.of_node;
drivers/i2c/busses/i2c-wmt.c:424: adap->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-xgene-slimpro.c:564: adapter->dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-xiic.c:761: i2c->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-xlp9xx.c:434: priv->adapter.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-xlr.c:426: priv->adap.dev.of_node = pdev->dev.of_node;
drivers/i2c/busses/i2c-zx2967.c:573: i2c->adap.dev.of_node = pdev->dev.of_node;
This is very much standard procedure, at least in I2C land. The above
patch would allow us to remove all of the above and instead rely on
matching on the parent device's ->of_node. The more I think about it,
the more I'm convinced that that's actually the correct thing to do.
i2c_adapter.dev.of_node should only be used to override the parent's
device tree node.
Thierry
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