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

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Date:	Wed, 15 May 2013 10:00:07 +0900
From:	"Jongsung Kim" <neidhard.kim@....com>
To:	"'Stephen Warren'" <swarren@...dotorg.org>
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

Stephen Warren <swarren@...dotorg.org> :
> 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?

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.

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