On 02/08/2017 04:22 PM, Christopher Covington wrote:

quoted

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-    while (pl011_read(uap, REG_FR) & uap->vendor->fr_busy)
+    while ((pl011_read(uap, REG_FR) ^ uap->vendor->inv_fr)
+                        & uap->vendor->fr_busy)

I really think the XOR logic needs to be documented wherever it's
used. It's just too confusing.

References such as the following for basic bit operations like
setting, clearing, and toggling are easy enough to come by.

http://stackoverflow.com/questions/47981/how-do-you-set-clear-and-toggle-a-single-bit-in-c-c

I know what XOR does.  I was thinking a more high-level comment would be 
appropriate.  With E44, we want to ignore the BUSY bit and use TXFE instead. 
So was hoping to a comment that says that:

/* Normally, we poll until BUSY=0, but E44 says we should poll until TXFE=1 
instead. So with E44, we set fr_busy to TXFE, but we have to invert it. */

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