Date:   Fri, 9 Jun 2017 11:25:07 -0500
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>,
        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



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.
Then other stuff - devm, EPROBE_DEFER ...


-- 
regards,
-grygorii

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