[U-Boot] [PATCH 3/8] usb_kdb: only process events succesfully received

[Marek Vasut]

On 7/3/19 11:46 AM, Michal Suchánek wrote:
> On Tue, 2 Jul 2019 23:20:28 +0200
> Marek Vasut <marex at denx.de> wrote:
> 
>> On 7/2/19 9:31 PM, Michal Suchánek wrote:
>>> On Tue, 2 Jul 2019 20:38:27 +0200
>>> Marek Vasut <marex at denx.de> wrote:
>>>   
>>>> On 7/2/19 7:50 PM, Michal Suchánek wrote:  
>>>>> On Tue, 2 Jul 2019 18:58:54 +0200
>>>>> Marek Vasut <marex at denx.de> wrote:
>>>>>     
>>>>>> On 7/2/19 4:22 PM, Michal Suchánek wrote:    
>>>>>>> On Tue, 2 Jul 2019 15:11:07 +0200
>>>>>>> Marek Vasut <marex at denx.de> wrote:
>>>>>>>       
>>>>>>>> On 7/2/19 3:04 PM, Michal Suchánek wrote:      
>>>>>>>>> On Tue, 2 Jul 2019 13:58:30 +0200
>>>>>>>>> Marek Vasut <marex at denx.de> wrote:
>>>>>>>>>         
>>>>>>>>>> On 7/1/19 5:56 PM, Michal Suchanek wrote:        
>>>>>>>>>>> Causes unbound key repeat on error otherwise.
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Michal Suchanek <msuchanek at suse.de>
>>>>>>>>>>> ---
>>>>>>>>>>>  common/usb_kbd.c | 7 +++----
>>>>>>>>>>>  1 file changed, 3 insertions(+), 4 deletions(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/common/usb_kbd.c b/common/usb_kbd.c
>>>>>>>>>>> index cc99c6be0720..948f9fd68490 100644
>>>>>>>>>>> --- a/common/usb_kbd.c
>>>>>>>>>>> +++ b/common/usb_kbd.c
>>>>>>>>>>> @@ -339,10 +339,9 @@ static inline void usb_kbd_poll_for_event(struct usb_device *dev)
>>>>>>>>>>>  	struct usb_kbd_pdata *data = dev->privptr;
>>>>>>>>>>>  
>>>>>>>>>>>  	/* Submit a interrupt transfer request */
>>>>>>>>>>> -	usb_submit_int_msg(dev, data->intpipe, &data->new[0], data->intpktsize,
>>>>>>>>>>> -			   data->intinterval);
>>>>>>>>>>> -
>>>>>>>>>>> -	usb_kbd_irq_worker(dev);
>>>>>>>>>>> +	if (!usb_submit_int_msg(dev, data->intpipe, &data->new[0],          
>>>>>>>>>>
>>>>>>>>>> Shouldn't you propagate return value from this function ? It can return
>>>>>>>>>> ENOTSUPP.
>>>>>>>>>>        
>>>>>>>>>
>>>>>>>>> If it did then probing keyboard would fail and we would not get here.        
>>>>>>>>
>>>>>>>> So there is no chance this function could return an error here, ever ?
>>>>>>>> E.g. what if it's implemented and someone yanks the keyboard cable out
>>>>>>>> just at the right time ?      
>>>>>>>
>>>>>>> It returns errors all the time with dwc2. That's why we need to check
>>>>>>> for the error condition. We should not get here if probing the keyboard
>>>>>>> failed, though. So if the function is not supported we will not get
>>>>>>> here. Anyway, if it's not supported or the keyboard is missing it by
>>>>>>> definition cannot provide useful result so we should not process it.      
>>>>>>
>>>>>> Except you start ignoring the error value from e.g. malfunctioning
>>>>>> keyboard here, instead of propagating it, correct ?    
>>>>>
>>>>> It was never propagated to start with. The return value was not checked
>>>>> at all. What I do here is check the return value and not process the
>>>>> data on error whatever it contains (like the keypress returned last
>>>>> time valid data was received).    
>>>>
>>>> I can see a patch which checks usb_kbd_poll_for_event() return value.
>>>> Can you add one ?  
>>>
>>> What for? Apparently the keypress is processed in usb_kbd_irq_worker.
>>> So checking the return value is needed to decide if the worker should
>>> run, and is not particularly useful outside usb_kbd_poll_for_event. We
>>> could signal a getc() failure but do we have any code handling getc()
>>> failures?  
>>
>> I presume getc() might signal EOF if the underlying hardware fails.
>> But in general, it's a good practice to not ignore errors.
>>
> 
> It is not such a great idea. You might have multiple input hardware (ie
> serial and usb keyboard). What does it mean that usb keyboard failed in
> this context?

I'd say, the behavior is undefined ?

> So in my view the ultimate consumer of getc() has no use for the error
> so there is no point in propagating it.

Ignoring errors and not reporting them isn't nice either, so what other
option(s) do we have here ?