[PATCH 1/2] tty: pl011: Work around QDF2400 E44 stuck BUSY bit

[timur@codeaurora.org (Timur Tabi)]

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