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

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Tue, May 14, 2013 at 03:03:14PM -0600, Stephen Warren wrote:
> On 05/14/2013 01:15 AM, Jongsung Kim wrote:
> > Stephen Warren <swarren@wwwdotorg.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.

The PCellID value is a marker for primecells, and is common to all primecells
which implement the ID scheme.  It's the other ID registers you want. :)