CAM breaks USB [was Re: USB causing boot to hang]

[Alexander Motin]

On 06.12.2019 21:08, Steve Kargl wrote:
> On Fri, Dec 06, 2019 at 07:09:55PM -0500, Alexander Motin wrote:
>> On 06.12.2019 18:41, Steve Kargl wrote:
>>> On Fri, Dec 06, 2019 at 06:15:32PM -0500, Alexander Motin wrote:
>>>> On 06.12.2019 17:52, Steve Kargl wrote:
>>>>> On Fri, Dec 06, 2019 at 03:33:09PM -0700, Warner Losh wrote:
>>>>>> On Fri, Dec 6, 2019 at 3:31 PM Steve Kargl <sgk at troutmask.apl.washington.edu>
>>>>>> wrote:
>>>>>>> The problem seems to be caused 355010.  This is a commit to
>>>>>>> fix CAM, which seems to break USB.
>>>>>>>
>>>>>> Yes. mav@ made this change...
>>>>>>
>>>>> src/UPDATING seems to be missing an entry about CAM breaking USB.
>>>>
>>>> And also that moon is made of cheese. :-\
>>>
>>> Not sure what you mean. 
>>
>> I mean that if we are going to write there random fairy-tales, then I
>> prefer my moon.
>>
>> If serious, then my change did not change semantics of any existing
>> tunables, only the way some of them are implemented, so there was
>> nothing to write in UPDATING.
> 
> The system boots at 355009.
> The system hangs at 355010.
> 
> How about adding:  After revision 355010, the cam subsystem may cause
> the usb subsystem to hang during boot.  It is recommended to disable usb.
> 
> You even hint at problems in your original commit message.

All I told in the commit message, is that my change may not fix all
existing USB boot problems.  That is it.  Nothing more.  I would not
commit any change with known problems.  And I am still not convinced
that it is a problem of my change, not some other pre-existing problem
triggered by it.

-- 
Alexander Motin