Re: [PATCH 0/2] Fix Regression with AXP20X for 6.13-rc1

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 11 Dec 2024 21:58:26 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Tue, 10 Dec 2024 16:48:57 -0600
> Chris Morgan <macroalpha82@gmail.com> wrote:
> 
> > From: Chris Morgan <macromorgan@hotmail.com>
> > 
> > After performing a git bisect, I identified a commit that broke the
> > battery and charger driver for my AXP717 PMIC. This was caused by
> > commit e37ec3218870 ("mfd: axp20x: Allow multiple regulators").
> > 
> > After digging into it, it appears when mfd_add_devices was called with
> > a platform ID of PLATFORM_DEVID_NONE, the devm_iio_channel_get() call
> > made by the various AXP20X power drivers would not be able to generate
> > a dev_name(dev) for some reason, and the iio_channel_get() call used in
> > the devm_ helper would fall back to making a iio_channel_get_sys()
> > call. After the platform ID was updated, now iio_channel_get() is no
> > longer falling back to iio_channel_get_sys(). At least this is my
> > limited understanding of what happened.  
> 
> The dev_name(dev) not getting a name doesn't sound quite right to me.
> 
> Time to look at the ancient creaking ghost that is the iio_map handling. 
> 
> struct iio_channel *iio_channel_get(struct device *dev,
> 				    const char *channel_name)
> {
> 	const char *name = dev ? dev_name(dev) : NULL;
> 	struct iio_channel *channel;
> 
> 	if (dev) {
> 		channel = fwnode_iio_channel_get_by_name(dev_fwnode(dev),
> 							 channel_name);
> 		if (!IS_ERR(channel) || PTR_ERR(channel) != -ENODEV)
> 			return channel;
> 	}
> 
> 	return iio_channel_get_sys(name, channel_name);
> }
> EXPORT_SYMBOL_GPL(iio_channel_get);
> 
> We didn't invent the relevant phandle stuff in DT via the patch you point at
> so all that matters is what gets passed to that iio_channel_get_sys()
> 
> So key here is that dev should be set, so we are passing dev_name(dev) into
> iio_channel_get_sys()
> I'm guessing that changed... 
> 
> Ah.  The iio_maps in
> https://elixir.bootlin.com/linux/v6.12.4/source/drivers/iio/adc/axp20x_adc.c#L158
> are our problem. Those hardcode the consumer_dev name. The fix just changed
> those names. Back when this infrastructure was written we were in the world of
> board files, so everything was hard coded in them - or in an MFD like this
> it was treated as a singleton device.

(note this driver is a little newer than that era, but used that old infrastructure
none the less)

> 
> So as to how to fix it... Assuming the new device names are the same for all
> the mfd parts that make up each pmic, then you should be able to figure out the
>  extra the number and build the channel maps to allow you to find the numbered
> devices.
> 
> That's a lot lighter change than moving over to DT based phandles for all this.
> (which is the modern way to handle it).
> 
> As a cheeky check, just edit those maps to whatever IDs you have and see
> if it works.  Probably not an upstreamable solution but will confirm we have
> it correct.
> 
> Your patch works because we allow for some fuzzy matching (I can't remember
> why) that doesn't use the consumer device name.
> That works as long as there is only one instance.  I'm guessing all this
> mess came about because someone has a board with two of these devices. On such
> a board we need the precise matching including the device name.
> 

+CC Sasha.  Whilst looking for the problem patch, I noticed that fix
has gone into stable.  If this is a common problem, we may want to drop
that briefly until we have a fix in place for this side effect as
the original patch fixed a configuration that had (I think?) never worked,
but broke ones that did.  I've no idea how common the devices are in
each configuration!

Jonathan


> Jonathan
> 
> > 
> > To fix this, I added a new devm_ helper of devm_iio_channel_get_sys()
> > that directly calls iio_channel_get_sys(), and I updated all the
> > affected drivers with the new routine. I then no longer experienced
> > any issues with the drivers on my devices.
> > 
> > Chris Morgan (2):
> >   iio: core: Add devm_ API for iio_channel_get_sys
> >   power: supply: axp20x: Use devm_iio_channel_get_sys() for iio chans
> > 
> >  drivers/iio/inkern.c                    | 18 ++++++++++++++++++
> >  drivers/power/supply/axp20x_ac_power.c  |  4 ++--
> >  drivers/power/supply/axp20x_battery.c   | 16 ++++++++--------
> >  drivers/power/supply/axp20x_usb_power.c |  6 +++---
> >  include/linux/iio/consumer.h            | 20 ++++++++++++++++++++
> >  5 files changed, 51 insertions(+), 13 deletions(-)
> >   
>