Hi Andy,
On 15/05/14 18:32, Andy Gross wrote:
On Fri, May 02, 2014 at 01:08:27PM -0500, Andy Gross wrote:
On Fri, May 02, 2014 at 09:58:41PM +0530, Vinod Koul wrote:
On Thu, Apr 17, 2014 at 05:04:02PM -0500, Andy Gross wrote:
This patch adds APIs that allow for BAM hardware flags to be set per
descriptor. Each one of the new flags informs the attached peripheral of a
special behavior that is required.
The EOT flag requests that the peripheral assert an end of transaction interrupt
when that descriptor is complete. It also results in special signaling protocol
that is used between the attached peripheral and the core using the DMA
controller.
DMA_PREP_INTERRUPT ??
I have 3 different IRQs that can be asserted based on the bit I set in the
hardware descriptor. The normal IRQ is the INT bit. However, in some cases the
peripheral protocol requires the use of the EOT or EOB interrupt instead. The
DMA_PREP_INTERRUPT would only work if I had only 2 choices.
Thinking about this more, I could use the DMA_PREP_INTERRUPT to cover the EOT
flag. However, I might get in a bind later if I need to support the EOB (end of
block) interrupt.
This is good start, mapping EOT to DMA_PREP_INTERRUPT seems to be much
appropriate. This will also provide mmci driver with much more generic
interface than the bam specific function calls.
Only way forward is to tie up this descriptor specific flags to more
generic flags. Having specific callbacks would introduce limitations in
using generic device drivers.
Not really sure how we can map EOB/NWD flags without really defining new
flags. Mapping to other generic flags might be totally confusing to
people using/interpreting those flags. Needs more discussion on this.
--srini
The NWD flag requests that the peripheral wait until the data has been fully
processed before signaling an interrupt.
interrupt for transaction complete or DMA request?
This is a special signaling mechanism that holds off the DMA interrupt until the
peripheral actually acks that the data has been processed completely. This is
required in many cases by the peripheral. One example is the SPI controller.
At the end of a transaction you are supposed to set the NWD so that the chip
select is de-asserted.
I'm not sure what flag I could map this to... maybe DMA_CTRL_ACK? or maybe the
DMA_PREP_FENCE? I don't generally like overloading the flags and slightly
twisting their intent. Could we add a flag to denote device ACK?
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