#12779 NORM Future : XO-4 custom build hangs SD bus for mmc0 on resume

[Zarro Boogs per Child]

#12779: XO-4 custom build hangs SD bus for mmc0 on resume
------------------------------+---------------------------------------------
           Reporter:  Quozl   |       Owner:  Quozl                            
               Type:  defect  |      Status:  assigned                         
           Priority:  normal  |   Milestone:  Future Release                   
          Component:  kernel  |     Version:  Development build as of this date
         Resolution:          |    Keywords:                                   
        Next_action:  design  |    Verified:  0                                
Deployment_affected:  au      |   Blockedby:                                   
           Blocking:          |  
------------------------------+---------------------------------------------
Changes (by Quozl):

  * next_action:  diagnose => design


Comment:

 The cause of the problem is that an interrupt from the wireless card
 arrives in the short time between the host instructing the card not to
 send interrupts, and before the host has slept.  This time is really
 short, of the order of a millisecond, so it is hard to hit.

 While the secure digital host controller interface (SDHCI) is being
 declocked and shut down for sleep, the interrupt arrives, and so the
 card registers cannot be read to clear the interrupt.  The thread that
 is trying to read the registers gives up, with a consequent lockup of
 the driver.

 The patches allow this thread to try again after the system has woken,
 and correct a few other matters that prevent reliable sleep and wake
 commands.

 This results in the laptop continuing to be usable.  The problem still
 occurs, but the effects on the laptops in my test bed are minimal.

 The remaining effect to be fixed is that the laptop stays asleep when
 it should have woken to respond to a network packet.

  * [http://dev.laptop.org/~quozl/y/1WiIZK.txt kernel changes being
 tested],
  * [http://dev.laptop.org/~quozl/z/1WiIZU.txt sample log of recovery after
 failure], see message timestamp 606.491989.

-- 
Ticket URL: <http://dev.laptop.org/ticket/12779#comment:18>
One Laptop per Child <http://laptop.org/>
One Laptop per Child bug tracking system