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SubjectRe: [PATCH v5 3/3] drivers:power:twl4030-charger: add deferred probing for phy and iio
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On 06/09/2017 01:05 AM, H. Nikolaus Schaller wrote:
> Hi,
>
>> Am 07.06.2017 um 22:44 schrieb Sebastian Reichel <sre@kernel.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@goldelico.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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