Date:   Fri, 9 Jun 2017 08:05:15 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     NeilBrown <neil@...wn.name>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Marek Belisko <marek@...delico.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-pm@...r.kernel.org, letux-kernel@...nphoenux.org,
        notasas@...il.com, linux-omap@...r.kernel.org
Subject: Re: [PATCH v5 3/3] drivers:power:twl4030-charger: add deferred probing for phy and iio

Hi,

> Am 07.06.2017 um 22:44 schrieb Sebastian Reichel <sre@...nel.org>:
> 
> Hi,
> 
> On Sun, May 21, 2017 at 12:38:18PM +0200, H. Nikolaus Schaller wrote:
>> This fixes an issue if both this twl4030_charger driver and
>> phy-twl4030-usb are compiled as modules and loaded in random order.
>> It has been observed on GTA04 and OpenPandora devices that in worst
>> case the boot process hangs and in best case the AC detection fails
>> with a warning.
>> 
>> Therefore we add deferred probing checks for the usb_phy and the
>> iio channel for AC detection.
>> 
>> For implementing this we must reorder code because we can't safely
>> return -EPROBE_DEFER after allocating any devm managed interrupt
>> (it might already/still be enabled without working interrupt handler).
>> 
>> So the check for required resources that may abort probing by
>> returning -EPROBE_DEFER, must come first.
> 
> This sounds fishy. EPROBE_DEFER should not be different from
> other error codes in this regard and devm_ requested resources
> should be free'd on any error. Why is irq handler not working?

1. there is no other error code involved, before we try to convert the driver to handle EPROBE_DEFER.
So it is not that EPROBE_DEFER is special but that we add an error return path for it.

2. I don't know why it is not working - I just know that the handler seems to be triggered before
all resources are available (if probe() is aborted with EPROBE_DEFER error paths) which ends up in kernel panics.

Therefore just to be safe, I have reordered things a little (without changing the function):

1. check for resources (with some EPROBE_DEFER)
2. allocate non-devm (with optional EPROBE_DEFER)
3. allocate devm

So this should be safe in any case.

Please also compare a discussion

https://lkml.org/lkml/2013/2/22/65

> 
>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>> ---
>> drivers/power/supply/twl4030_charger.c | 37 ++++++++++++++++++++--------------
>> 1 file changed, 22 insertions(+), 15 deletions(-)
>> 
>> diff --git a/drivers/power/supply/twl4030_charger.c b/drivers/power/supply/twl4030_charger.c
>> index 785a07bc4f39..945eabdbbc89 100644
>> --- a/drivers/power/supply/twl4030_charger.c
>> +++ b/drivers/power/supply/twl4030_charger.c
>> @@ -984,6 +984,28 @@ static int twl4030_bci_probe(struct platform_device *pdev)
>> 
>> 	platform_set_drvdata(pdev, bci);
>> 
>> +	if (bci->dev->of_node) {
>> +		struct device_node *phynode;
>> +
>> +		phynode = of_find_compatible_node(bci->dev->of_node->parent,
>> +						  NULL, "ti,twl4030-usb");
>> +		if (phynode) {
>> +			bci->transceiver = devm_usb_get_phy_by_node(
>> +				bci->dev, phynode, &bci->usb_nb);
>> +			if (IS_ERR(bci->transceiver) &&
>> +			    PTR_ERR(bci->transceiver) == -EPROBE_DEFER)
>> +				return -EPROBE_DEFER;	/* PHY not ready */
>> +		}
>> +	}
>> +
>> +	bci->channel_vac = iio_channel_get(&pdev->dev, "vac");
>> +	if (IS_ERR(bci->channel_vac)) {
>> +		if (PTR_ERR(bci->channel_vac) == -EPROBE_DEFER)
>> +			return -EPROBE_DEFER;	/* iio not ready */
>> +		dev_warn(&pdev->dev, "could not request vac iio channel");
>> +		bci->channel_vac = NULL;
>> +	}
>> +
> 
> You should not request non-devm managed iio_channel before
> devm-managed power-supply.

Well, it is not *me* doing that.

It is the unpatched driver which already does. See:

	https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/power/supply/twl4030_charger.c?h=v4.12-rc4#n1069

I have just moved this line to a different location to be able to add a proper EPROBE_DEFER return path.

> This could be fixed by switching to
> devm_iio_channel_get(), which also cleans up some code.

Yes, this could be an alternative solution.
We still need EPROBE_DEFER handling.

> 
> I suspect, that this is also your IRQ problem, since iio_channel
> is currently free'd before irqs are free'd, but its used in irq
> code.

Hm. No.

In upstream code it is never freed on probe failure because there is only
an error return (goto fail) after allocating irqs in case the
twl_i2c_write_u8 fails. Which usually doesn't.

The EPROBE_DEFER returned by iio_channel_get not being ready simply prints
a warning and turns off AC detection (bci->channel_vac = NULL) forever.

> 
>> 	bci->ac = devm_power_supply_register(&pdev->dev, &twl4030_bci_ac_desc,
>> 					     NULL);
>> 	if (IS_ERR(bci->ac)) {
>> @@ -1017,25 +1039,10 @@ static int twl4030_bci_probe(struct platform_device *pdev)
>> 		return ret;
>> 	}
>> 
>> -	bci->channel_vac = iio_channel_get(&pdev->dev, "vac");
>> -	if (IS_ERR(bci->channel_vac)) {

My first attempt to fix EPROBE_DEFER was to add this

+		if (PTR_ERR(bci->channel_vac) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;	/* iio not ready */

>> -		bci->channel_vac = NULL;
>> -		dev_warn(&pdev->dev, "could not request vac iio channel");
>> -	}
>> -
>> 	INIT_WORK(&bci->work, twl4030_bci_usb_work);
>> 	INIT_DELAYED_WORK(&bci->current_worker, twl4030_current_worker);
>> 
>> 	bci->usb_nb.notifier_call = twl4030_bci_usb_ncb;
>> -	if (bci->dev->of_node) {
>> -		struct device_node *phynode;
>> -
>> -		phynode = of_find_compatible_node(bci->dev->of_node->parent,
>> -						  NULL, "ti,twl4030-usb");
>> -		if (phynode)
>> -			bci->transceiver = devm_usb_get_phy_by_node(
>> -				bci->dev, phynode, &bci->usb_nb);

and this

+			if (IS_ERR(bci->transceiver) &&
+			    PTR_ERR(bci->transceiver) == -EPROBE_DEFER) {
+				ret = -EPROBE_DEFER;	/* PHY not ready */
+				goto fail;

This did run (and potentially return) after installing devm_request_threaded_irq leading
to observation of severe kernel panics by interrupts.

Moving the iio channel allocation before devm_request_threaded_irq made them go away.

>> -	}
>> 
>> 	/* Enable interrupts now. */
>> 	reg = ~(u32)(TWL4030_ICHGLOW | TWL4030_ICHGEOC | TWL4030_TBATOR2 |
> 
> -- Sebastian

How important is it to keep the current sequence of devm_request_threaded_irq() + (devm_)iio_channel_get() untouched?

The reason I ask is that it is more likely for (devm_)iio_channel_get() to fail than devm_request_threaded_irq().

Hence the iio channel should imho be always allocated first, so that we skip allocating+freeing unused irq handlers in case
of iio not being ready.

Therefore, I suggest to keep the proposed reordering even if we think devm-conversion of iio_channel_get() alone
would solve it equally well.

Next: should there be two separate patches? One for converting the non-devm iio_channel_get() and cleaning up error path.
And one for adding EPROBE_DEFER error path.

Or keep it in a single patch because they only make sense if done together (you can't add/remove deferred probing
without converting and/or moving iio_channel_get())?

So please advise how to proceed.

BR and thanks,
Nikolaus


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