[PATCH] amba-pl011: support hardware flow control

[jamie@shareable.org (Jamie Lokier)]

Russell King - ARM Linux wrote:
> On Wed, Feb 10, 2010 at 01:16:37AM +0000, Jamie Lokier wrote:
> > Russell King - ARM Linux wrote:
> > > This means that when the kernel's buffers fill up, the kernel calls
> > > down to the serial core layer to throttle the input.  This then
> > > calls into the set_mctrl function to de-assert RTS.  However, because
> > > the hardware ignores the requested software state, the RTS signal
> > > is not de-asserted, and the remote end continues sending data.
> > > 
> > > So, enabling hardware auto-RTS is bad news - you will lose data if
> > > the application stops reading data.
> > 
> > Surely the driver can just stop reading from the UART when the
> > kernel's buffers are full and hardware-RTS is enabled.  Then the
> > hardware will deassert RTS itself.
> 
> I'll let you work out how to implement that.

You have a point.

What do you think of the other suggestion, switching between
software-RTS+deasserted and hardware-RTS in response to set_mctrl
calls from the generic serial layer - effectively hardware-RTS with
ability for kernel to force it deasserted?

-- Jamie