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From: Zhang Zhen <email@example.com>
To: Tim Kryger <firstname.lastname@example.org>
Cc: Alan Cox <email@example.com>,
Peter Hurley <firstname.lastname@example.org>,
Linux Kernel Mailing List <email@example.com>,
<firstname.lastname@example.org>, Jamie Iles <email@example.com>,
Arnd Bergmann <firstname.lastname@example.org>, <email@example.com>,
Wang Kai <firstname.lastname@example.org>
Subject: Re: [RFC] With 8250 Designware UART, if writes to the LCR failed the kernel will hung up
Date: Tue, 10 Mar 2015 11:15:48 +0800 [thread overview]
Message-ID: <54FE61E4.email@example.com> (raw)
On 2015/3/10 10:47, Tim Kryger wrote:
> On Mon, Mar 9, 2015 at 8:05 AM, Alan Cox <firstname.lastname@example.org> wrote:
>> Ah no - I meant what is their official software workaround for existing
>> parts with the bug ? Presumably they have an errata document that
>> discusses this and the correct methods they recommend to avoid the
>> hang ?
> As far as I know, the only advice they provided was rather naive.
> The documentation I saw suggested stashing a copy of the LCR and then
> rewriting it when the special LCR write failed interrupt was raised.
> That approach was not workable as the LCR might be written while the
> interrupt is masked causing the sequence of register writes to occur
> in an order other than what was desired.
> Additionally, when the LCR needed to be re-written but the UART stayed
> busy, the interrupt would keep firing and the driver would starve out
> everything else on the CPU.
> The current workaround of clearing fifos and retrying a fixed number
> of times isn't ideal but I'm not sure what else can be done given the
> way this hardware works.
> Additional background is in c49436b657d0a56a6ad90d14a7c3041add7cf64d
If writes to the LCR failed and the dev_err in dw8250_serial_out lead to
the system hung up.
The root cause is that serial8250_console_write try to get port->lock which
has been got by serial8250_do_set_termios.
"Writes to the LCR are used to change the baud rate, parity, stop bit,
or data length so the data that may be lost is likely not important."
The dev_err in dw8250_serial_out must be needed? We can delete dev_err directly ?
next prev parent reply other threads:[~2015-03-10 3:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-06 9:11 Zhang Zhen
2015-03-06 16:50 ` Peter Hurley
2015-03-07 3:01 ` Tim Kryger
2015-03-09 7:10 ` long.wanglong
2015-03-09 13:32 ` Alan Cox
2015-03-09 14:36 ` Tim Kryger
2015-03-09 15:05 ` Alan Cox
2015-03-10 2:47 ` Tim Kryger
2015-03-10 3:15 ` Zhang Zhen [this message]
2015-03-10 13:25 ` Peter Hurley
2015-03-11 1:20 ` Zhang Zhen
2015-03-13 15:36 ` Andy Shevchenko
2015-03-15 14:50 ` Peter Hurley
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