On 04/06/2016 10:48 AM, Uwe Kleine-König wrote:
> Hello,
>
> On Wed, Apr 06, 2016 at 08:23:02AM -0700, Peter Hurley wrote:
>> On 04/05/2016 11:20 PM, Uwe Kleine-König wrote:
>>> On Tue, Apr 05, 2016 at 09:58:09AM -0700, Peter Hurley wrote:
>>>> On 04/05/2016 06:25 AM, Yegor Yefremov wrote:
>>>>> On Tue, Apr 5, 2016 at 2:21 PM, Uwe Kleine-König
>>>>> <u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
>>>>>> On Tue, Apr 05, 2016 at 12:32:53PM +0200, Yegor Yefremov wrote:
>>>>>>> I've got a kernel crash from kernel robot. If we use UART before
>>>>>>> general initialization (earlyprintk), then any call to mctrl API would
>>>>>>> result in NULL pointer dereference. One solution would be to check, if
>>>>>>> gpios IS_ERR_OR_NULL(). See below:
>>>>>>>
>>>>>>> --- a/drivers/tty/serial/serial_mctrl_gpio.c
>>>>>>> +++ b/drivers/tty/serial/serial_mctrl_gpio.c
>>>>>>> @@ -54,6 +54,9 @@ void mctrl_gpio_set(struct mctrl_gpios *gpios,
>>>>>>> unsigned int mctrl)
>>>>>>> int value_array[UART_GPIO_MAX];
>>>>>>> unsigned int count = 0;
>>>>>>>
>>>>>>> + if (IS_ERR_OR_NULL(gpios))
>>>>>>> + return;
>>>>>>> +
>>>>>>> for (i = 0; i < UART_GPIO_MAX; i++)
>>>>>>> if (gpios->gpio[i] && mctrl_gpios_desc[i].dir_out) {
>>>>>>> desc_array[count] = gpios->gpio[i];
>>>>>>
>>>>>> IS_ERR_OR_NULL(gpios) should never be true. gpios should be the value
>>>>>> that was returned by mctrl_gpio_init, this never returns NULL and if it
>>>>>> returns an error you're supposed to not register the port. And for early
>>>>>> printk there is AFAIK no mctrl involved.
>>>>>
>>>>> You're right. it was console_init stuff. It happens before
>>>>> serial8250_register_8250_port(). Perhaps I should introduce one more
>>>>> gpio_init invocation in univ8250_console_setup().
>>>
>>> If the port isn't registered yet, nobody should call the port's
>>> .set_mctrl. So your plan sounds wrong for this reason, too.
>>
>> The 8250 driver initializes MCR from mctrl in its set_termios method:
>
> MCR is a register and mctrl a member of struct port, right?
Yes. mctrl is the serial core's abstraction of the _modem control_ line state.
MCR is the hardware implementation of that abstraction.
>> uart_set_options
>> mctrl |= TIOCM_DTR
>> ->set_termios => serial8250_set_termios
>> serial8250_set_mctrl
>
> Then maybe the bug is that uart_set_options calls serial8250_set_mctrl
> which is supposed to be only called after the device is probed?
Nope; DTR should be asserted when the console is initialized.
I understand that is not possible with the mctrl helpers right now,
but that's no reason to break other setups that do the right thing.
>>>> Just skip mctrl_gpio_set() and mctrl_gpio_get*() if !up->gpios
>>>
>>> This would work, but sounds wrong for the above reason, too. I'd like to
>>> reserve gpios=NULL for the case where no gpio has to be controlled, so
>>> please don't use it as indication if mctrl_gpio_init was called.
>>
>> I'm confused; what operations will be different if gpios==NULL?
>> And wouldn't that argue for checking gpios==NULL in mctrl_gpio_set(),
>> performing no action in that case?
>
> OK, the right thing would happen. Still I'd prefer if a serial driver
> did not try to interpret what a certain value means or not. I'd say the
> only allowed operations on a gpios value are calling mctrl_gpio
> functions and use IS_ERR and PTR_ERR during probe.
Ok, so then we're back to checking gpios == NULL in mctrl_gpio_set()
instead, right?
Because that's "the case where no gpio has to be controlled" because
there is no gpio yet.
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