linux-kernel - Re: [PATCH] ARM: PL011: add support for extended FIFO-size of PL011-r1p5

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Message-ID: <519AD82A.6090809@wwwdotorg.org>
Date:	Mon, 20 May 2013 20:12:58 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Jongsung Kim <neidhard.kim@....com>
CC:	'Russell King' <linux@....linux.org.uk>,
	'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>,
	jslaby@...e.cz, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: PL011: add support for extended FIFO-size of PL011-r1p5

On 05/20/2013 07:39 PM, Jongsung Kim wrote:
> Jongsung Kim <neidhard.kim@....com> :
>> Stephen Warren <swarren@...dotorg.org> :
>>>> All r1p5 have 32-byte FIFO depth and it's not configurable. From the 
>>>> PL011
>>>> TRM:
>>>>
>>>> r1p4-r1p5	Contains the following differences in functionality:
>>>> 		* The receive and transmit FIFOs are increased to a depth of
> 32.
>>>> 		* The Revision field in the UARTPeriphID2 Register on page
> 3-24
>>>> 		  bits [7:4] now reads back as 0x3.
>>>
>>> Well, that certainly isn't true in practice. I think we should revert 
>>> this commit until we can determine what the problem is.
>>
>> I asked to the ARM support about this. Waiting for reply..
> 
> ARM support said they doesn't have information about BCM2835 UART. Does
> anyone have a communication channel to Broadcom? It takes time for me to
> get contact point to Broadcom.. (I'm trying)
> 
> However, ARM support also said:
> 
> "If the Broadcom part definitely has 16-deep FIFOs, it cannot be based
> on a PL011 r1p5, so I might guess that Broadcom have just referenced
> the latest version of the documentation on our website, but have actually
> implemented an earlier version."

This all seems rather academic. Irrespective of what the cause of the
problem is, the commit actively breaks a previously working
configuration. I still believe we should revert it first, then find out
exactly what's going on later. Should I sent the revert commit?

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