[PATCH] staging: comedi: cb_pcidas: reinstate delay removed from trimpot setting

Ian Abbott abbotti at mev.co.uk
Mon Nov 2 10:25:25 UTC 2020


On 29/10/2020 14:18, Ian Abbott wrote:
> Commit eddd2a4c675c ("staging: comedi: cb_pcidas: refactor
> write_calibration_bitstream()") inadvertently removed one of the
> `udelay(1)` calls when writing to the calibration register in
> `cb_pcidas_calib_write()`.  Reinstate the delay.  It may seem strange
> that the delay is placed before the register write, but this function is
> called in a loop so the extra delay can make a difference.
> 
> This _might_ solve reported issues reading analog inputs on a
> PCIe-DAS1602/16 card where the analog input values "were scaled in a
> strange way that didn't make sense".  On the same hardware running a
> system with a 3.13 kernel, and then a system with a 4.4 kernel, but with
> the same application software, the system with the 3.13 kernel was fine,
> but the one with the 4.4 kernel exhibited the problem.  Of the 90
> changes to the driver between those kernel versions, this change looked
> like the most likely culprit.

Actually, I've realized that this patch will have no effect on the 
PCIe-DAS1602/16 card because it uses a different driver - cb_pcimdas, 
not cb_pcidas.

Greg, you might as well drop this patch if you haven't already applied 
it, since it was only a hunch that it fixed a problem.

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