Re: [PATCH] [RFC] dmaengine: add fifo_size member

From: Sameer Pujar
Date: Mon Jun 24 2019 - 22:57:50 EST

On 6/24/2019 11:56 AM, Vinod Koul wrote:
On 20-06-19, 15:59, Sameer Pujar wrote:

So can you explain me what is the difference here that the peripheral
cannot configure and use burst size with passing fifo depth?
Say for example FIFO_THRESHOLD is programmed as 16 WORDS, BURST_SIZE as 8
ADMAIF does not push data to AHUB(operation [2]) till threshold of 16 WORDS
reached in ADMAIF FIFO. Hence 2 burst transfers are needed to reach the
As mentioned earlier, threshold here is to just indicate when data transfer
can happen
to AHUB modules.
So we have ADMA and AHUB and peripheral. You are talking to AHUB and that
is _not_ peripheral and if I have guess right the fifo depth is for AHUB
Yes the communication is between ADMA and AHUB. ADMAIF is the interface
ADMA and AHUB. ADMA channel sending data to AHUB pairs with ADMAIF TX
Similary ADMA channel receiving data from AHUB pairs with ADMAIF RX channel.
FIFO DEPTH we are talking is about each ADMAIF TX/RX channel and it is
DMA transfers happen to/from ADMAIF FIFOs and whenever data(per WORD) is
out of ADMAIF to/from AHUB, asseration is made to ADMA. ADMA keeps counters
based on
these assertions. By knowing FIFO DEPTH and these counters, ADMA knows when
to wait or
when to transfer data.
Where does ADMAIF driver reside in kernel, who configures it for normal
dma txns..?
Not yet, we are in the process of upstreaming ADMAIF driver.
To describe briefly, audio subsystem is using ALSA SoC(ASoC) layer. ADMAIF is
registered as platform driver and exports DMA functionality. It registers PCM
devices for each Rx/Tx ADMAIF channel. During PCM playback/capture operations,
ALSA callbacks configure DMA channel using API dmaengine_slave_config().
RFC patch proposed, is to help populate FIFO_SIZE value as well during above
call, since ADMA requires it.

Also it wold have helped the long discussion if that part was made clear
rather than talking about peripheral all this time :(
Thought it was clear, though should have avoided using 'peripheral' in the
discussions. Sorry for the confusion.