Date:   Sat, 10 Jun 2017 06:59:08 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     Sebastian Reichel <sre@...nel.org>, 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 Grygorii,

> Am 09.06.2017 um 18:25 schrieb Grygorii Strashko <grygorii.strashko@...com>:
> 
> 
> 
> On 06/09/2017 01:05 AM, H. Nikolaus Schaller wrote:
>> 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.
>> 
> 
> You should request irq as late as possible in probe - it's safest way to go always.
> You see crushes simply because request_irq enables IRQ and IRQ can trigger immediately, so
> IRQ handler will run and all required resources should be ready and initialized.
> 
> In this case:
> twl4030_bci_interrupt() -> twl4030_charger_update_current() -> ac_available() -> iio_read_channel_processed()
> OOOPS.
> 
> So, first thing to do is to reorder probe to ensure that sequence is safe.

That is exactly what I guessed when proposing the reordering patch.

> Then other stuff - devm, EPROBE_DEFER ...

IMHO, reordering alone doesn't make much sense as a single patch. Or does it?

BR and thanks,
Nikolaus

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