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

[Chris Morgan <macroalpha82@gmail.com>]

On Tue, Dec 17, 2024 at 02:04:37AM +0800, Chen-Yu Tsai wrote:
> On Tue, Dec 17, 2024 at 2:01 AM Chris Morgan <macroalpha82@gmail.com> wrote:
> >
> > On Wed, Dec 11, 2024 at 09:58:26PM +0000, Jonathan Cameron 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.
> > >
> > > 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.
> >
> > Is there a way to figure out the device number at runtime? The issue is
> > each time the device attempts to probe and fails, the device number
> > increments, making it a "hitting a moving target" problem.
> 
> The ADC device is a mfd cell or child device of the PMIC mfd device.
> So you should be able to use dev->parent to get it directly? We do
> that at least for the regulator driver.

Sorry to dig up such an old thread. I'm taking a look at this one again
and can confirm passing pdev->dev.parent to devm_iio_channel_get() is
insufficient to get the driver to find the correct ADC channel. Would
there be another/better way to do this other than the
devm_iio_channel_get_sys() as proposed? Or should we be walking the
parent somehow looking for the named ADC channel on each child device
(which would also require a new symbol most likely)?

Thank you,
Chris

> 
> ChenYu
> 
> > Thank you,
> > Chris
> >
> > >
> > > 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.
> > >
> > > 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(-)
> > > >
> > >