From: Theodore Ts'o <tytso@mit.edu>
To: Prasad Koya <prasad.koya@gmail.com>
Cc: linux-serial@vger.kernel.org, gregkh@linuxfoundation.org
Subject: Re: UART_IIR_BUSY set for 16550A
Date: Sat, 24 May 2014 20:36:42 -0400 [thread overview]
Message-ID: <20140525003642.GC6946@thunk.org> (raw)
In-Reply-To: <CAGXD9Ocoo_sUnFmd-pfU52yUQ5oPjWxAHXjvP8facuMiOSUn5w@mail.gmail.com>
On Fri, May 23, 2014 at 10:08:49AM -0700, Prasad Koya wrote:
>
> I don't see anyone in kernel using UART_IIR_BUSY bit except Designware
> serial driver. We are using 8250 driver for our 16550A and
> occasionally we see UART_IIR_BUSY set and soon after that console is
> hosed. In what situations is this bit set? I don't see much
> documentation for this.
UART_IIR_BUSY is not a bit, it's a magic bit pattern, which is I
believe a Designware-specific hack. As far as standard
8250-compatible UART's are concerned, if the low bit (bit 0) is set in
the IIR register, there are no interrupts pending, and so you
shouldn't need to check the 0x06 bits (i.e., bits 1 and 2).
- Ted
next prev parent reply other threads:[~2014-05-25 0:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-23 17:08 UART_IIR_BUSY set for 16550A Prasad Koya
2014-05-25 0:36 ` Theodore Ts'o [this message]
2014-05-25 1:22 ` Prasad Koya
2014-05-25 2:44 ` Theodore Ts'o
2014-05-25 6:21 ` Prasad Koya
2014-05-25 12:04 ` Theodore Ts'o
2014-05-27 23:33 ` Prasad Koya
2014-05-28 5:03 ` Theodore Ts'o
2014-05-28 5:47 ` Prasad Koya
2014-05-29 6:18 ` Theodore Ts'o
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