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

[Marek Vasut]

On 7/3/19 6:41 PM, Michal Suchánek wrote:
> On Wed, 3 Jul 2019 13:48:00 +0200
> Marek Vasut <marex at denx.de> wrote:
> 
>> On 7/3/19 1:43 PM, Michal Suchánek wrote:
>>> On Wed, 3 Jul 2019 13:26:50 +0200
>>> Marek Vasut <marex at denx.de> wrote:
>>>   
>>>> 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 ?  
>>>
>>> But we need to define it which the code does by ignoring the
>>> device-specific error and relying on devices that are still working
>>> (like a serial port) or for which error detection is not available
>>> (like most serial ports).  
>>
>> Maybe the error should still be propagated to the input layer , and not
>> ignored at the USB layer ?
> 
> Maybe. I would leave the discussion of handling errors in the input
> layer for a separate patchset.

It's literally 3-line change to make usb_kbd_poll_for_event() return the
error code.

>>>>> 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 ?  
>>>
>>> Ignoring the errors is exactly the desirable behavior when facing
>>> broken hardware like dwc2. On non-broken hardware you will get fewer
>>> errors to ignore. It is up to the device driver to report device
>>> failure with a message when the error condition could be informative to
>>> the user (such as previously working device going away completely).  
>>
>> I thought this error is a keyboard failure though , and has nothing to
>> do with the USB controller ?
> 
> As far as I know the keyboard is working fine but the controller is
> failing to deliver some messages.

Uh, would you be willing to debug that ?

[...]