DCD interrupt for i.MX25 UART

[Uwe Kleine-König]

Hallo Lothar,

On Tue, Mar 29, 2016 at 01:14:43PM +0200, Lothar Waßmann wrote:
> On Wed, 23 Mar 2016 16:36:38 +0100 Uwe Kleine-König wrote:
> > Hello,
> > 
> > I have a problem with an UART on an i.MX25 based machine. I implemented
> > DCD (and other handshake lines) irq handling[1].
> > 
> > Now a user of this patch noticed that DCD handling (at least) is broken.
> > The problem is that the USR2_DCDDELT bit doesn't clear:
> > 
> > 	root at hostname:~ memtool md 0x43f90080+0x34  
> > 	43f90080: 00000000 00004021 0000078c 00004002                ....!@....... at ..
> > 	43f90090: 00000b41 00002040 00005268 0000002b                A...@ ..hR..+...
> > 	43f900a0: 00000000 000000bf 00002e62 00000008                ........b.......
> > 	43f900b0: 0000251c                                           .%..
> > 
> > 	root at hostname:~ memtool mw 0x43f90098 0x0x40
>                                               ^^^^^^
> This looks rather fishy.

Probably a cut-and-paste problem. I tried this several times with
various values, the bit doesn't clear.

> > 	root at hostname:~ memtool md 0x43f90080+0x34  
> > 	43f90080: 00000000 00004021 0000078c 00004002                ....!@....... at ..
> > 	43f90090: 00000b41 00002040 00005268 0000002b                A...@ ..hR..+...
> > 	43f900a0: 00000000 000000bf 00002e62 00000008                ........b.......
> > 	43f900b0: 0000251c                                           .%..
> > 
> > In fact even writing 0xffff doesn't change the register, where I would expect
> > that the DCDDELT bit (0x40) disappears. I'm sure there is nothing toggling this
> > line.
> > 
> Are you sure the clock is enabled when doing your manual tests?

I guess they are. For sure the same thing happens with the driver active
and the device open. And the symptoms are the same: If the DCDDELTA irq
is enabled and active the machine is stuck until the irq upper layers
disable the respective irq.

Best regards
Uwe

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