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

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Date:	Tue, 14 May 2013 15:03:14 -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 05/14/2013 01:15 AM, Jongsung Kim wrote:
> Stephen Warren <swarren@...dotorg.org> :
>> For reference, the AMBA periphid of the UART device there is 0x00341011.
>> The nibble "3" is the revision being tested in:
> 
> The UART device has periphid 0x00341011, and is compatible with the
> original PL011 prior to r1p5. Not with r1p5. It could be a possible
> way to specify the compatible periphid (such as 0x00241011) instead
> of just 0x0 when initializing the amba_device for the UART.
> 
>>> +static unsigned int get_fifosize_arm(unsigned int periphid)
>>> +{
>>> +	unsigned int rev = (periphid >> 20) & 0xf;
>>> +	return rev < 3 ? 16 : 32;
>>> +}
...
> Doesn't the BCM2835 UART have anything different from the ARM PL011?
> What about the UARTPCellID registers? They are set to 0xb105f00d with
> the ARM PL011.

Looking at BCM2835-ARM-Peripherals.pdf (i.e. the public documentation
for the BCM2835 chip), I see:

=====
The UART provides:
* Separate 16x8 transmit and 16x12 receive FIFO memory.
...
For the in-depth UART overview, please, refer to the ARM PrimeCell UART
(PL011) Revision: r1p5 Technical Reference Manual.
=====

That seems to imply that not all r1p5 PL011s actually have a depth-32
FIFO. Perhaps this is a configurable property of the IP block, not
something that all r1p5 have?

I can't check the UARTPCellID registers right now.
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