#12391 NORM 4-firmw: non-touchscreen SKU support

[Zarro Boogs per Child]

#12391: non-touchscreen SKU support
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           Reporter:  Quozl                |       Owner:  Quozl               
               Type:  enhancement          |      Status:  new                 
           Priority:  normal               |   Milestone:  4-firmware          
          Component:  ofw - open firmware  |     Version:  Development firmware
         Resolution:                       |    Keywords:                      
        Next_action:  add to build         |    Verified:  0                   
Deployment_affected:                       |   Blockedby:                      
           Blocking:                       |  
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Changes (by Quozl):

 * cc: pgf (added)


Comment:

 thanks, good point.

 no, TOUCH_HD# is an inverted signal, active low, and is an input to SoC,
 so the correct semantics are "if low, tri-state all touchscreen gpios".
 this is from page 3 of zForce_Communication_Interface_4_1.pdf and
 confirmed by observation on laptops with a touchscreen controller; the
 signal is high.

 what we are doing on non-touchscreen SKU is (a) not populating the
 microcontroller, and R266, and (b) pulling the TOUCH_HD# signal low by
 populating R273.  (R366 and R273 form the 3.3V to 1.8V level converter for
 the signal on the way to the SoC).

 for the linux driver you might either:
  * check TOUCH_HD# first, and if low, abandon device startup, or
  * defer device startup until TOUCH_HD# goes high.

 both will meet the goal of not providing a touchscreen software interface
 for a laptop that has no touchscreen controller.  the latter will allow
 debugging where TOUCH_HD# is held low on boot.  i imagine you would prefer
 the former.

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Ticket URL: <http://dev.laptop.org/ticket/12391#comment:3>
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