linux-kernel - Re: [RFC] With 8250 Designware UART, if writes to the LCR failed the kernel will hung up

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Date:	Mon, 09 Mar 2015 15:05:02 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	Tim Kryger <tim.kryger@...il.com>
Cc:	"long.wanglong" <long.wanglong@...wei.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Zhang Zhen <zhenzhang.zhang@...wei.com>,
	linux-serial@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tim Kryger <tim.kryger@...aro.org>, gregkh@...uxfoundation.org,
	Jamie Iles <jamie@...ieiles.com>,
	Arnd Bergmann <arnd@...db.de>, shenjiangjiang@...wei.com,
	Wang Kai <morgan.wang@...wei.com>
Subject: Re: [RFC] With 8250 Designware UART, if writes to the LCR failed
 the kernel will hung up

On Mon, 2015-03-09 at 07:36 -0700, Tim Kryger wrote:
> On Mon, Mar 9, 2015 at 6:32 AM, Alan Cox <alan@...ux.intel.com> wrote:
> >> Maybe the next release of the board we will upgrade the serial block to the new version.
> >> but the issue is that how we circumvent this problem in kernel?
> >
> > What is the official vendor workaround ?
> 
> They introduced a UART_16550_COMPATIBLE option for the IP which should
> be selected.
> 
> If configured, writes to the LCR are allowed even if it is "busy" so
> there is no need to retry.
> 
> More importantly there is no possibility of failing to write the LCR
> after numerous retries.


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 ?

Alan


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