#11311 HIGH 11.3.0: Secure boot makes Linux audio unusable on XO-1

[Zarro Boogs per Child]

#11311: Secure boot makes Linux audio unusable on XO-1
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           Reporter:  greenfeld            |       Owner:  wmb at firmworks.com
               Type:  defect               |      Status:  new              
           Priority:  high                 |   Milestone:  11.3.0           
          Component:  ofw - open firmware  |     Version:  not specified    
         Resolution:                       |    Keywords:                   
        Next_action:  diagnose             |    Verified:  0                
Deployment_affected:                       |   Blockedby:                   
           Blocking:                       |  
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Comment(by wmb at firmworks.com):

 The most likely cause is the phrase "0 4 my-w!" in dev/geode/ac97/ac97.fth
 :unmap-regs .

 That has the effect of turning off the decoding for the audio registers
 that otherwise appear in PCI memory space.

 Arguably, the Linux driver should turn on the register decoding for its
 device.  It's a general OFW policy to leave devices in the non-decoding
 state when they are not in use.

 In this case, we could violate that rule if necessary, but I'd like to
 understand whether or not the Linux driver could be changed to ensure that
 its registers are being decoded.

 The argument for OFW's "off unless used" policy is based on the fact that
 some PCI devices have multiple "windows" onto the same set of internal
 registers, and by enabling only the one that the driver is going to use,
 the risk of spurious access through the other one is minimized.

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Ticket URL: <http://dev.laptop.org/ticket/11311#comment:5>
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