[RFC PATCH 2/4] ASoC: soc-generic-dmaengine-pcm: Add custom prepare and submit function

[Sia, Jee Heng]

> -----Original Message-----
> From: Vinod Koul <vkoul at kernel.org>
> Sent: 18 November 2020 12:41 PM
> To: Sia, Jee Heng <jee.heng.sia at intel.com>
> Cc: Shevchenko, Andriy <andriy.shevchenko at intel.com>; Sit, Michael Wei Hong
> <michael.wei.hong.sit at intel.com>; alsa-devel at alsa-project.org; tiwai at suse.com;
> broonie at kernel.org; pierre-louis.bossart at linux.intel.com; Rojewski, Cezary
> <cezary.rojewski at intel.com>; liam.r.girdwood at linux.intel.com; lars at metafoo.de
> Subject: Re: [RFC PATCH 2/4] ASoC: soc-generic-dmaengine-pcm: Add custom
> prepare and submit function
> 
> On 18-11-20, 00:34, Sia, Jee Heng wrote:
> >
> >
> > > -----Original Message-----
> > > From: Andy Shevchenko <andriy.shevchenko at intel.com>
> > > Sent: 17 November 2020 11:51 PM
> > > To: Sit, Michael Wei Hong <michael.wei.hong.sit at intel.com>
> > > Cc: alsa-devel at alsa-project.org; tiwai at suse.com; broonie at kernel.org;
> > > pierre- louis.bossart at linux.intel.com; Rojewski, Cezary
> > > <cezary.rojewski at intel.com>; liam.r.girdwood at linux.intel.com; Sia,
> > > Jee Heng <jee.heng.sia at intel.com>; vkoul at kernel.org; lars at metafoo.de
> > > Subject: Re: [RFC PATCH 2/4] ASoC: soc-generic-dmaengine-pcm: Add
> > > custom prepare and submit function
> > >
> > > On Tue, Nov 17, 2020 at 04:03:48PM +0800, Michael Sit Wei Hong wrote:
> > > > Enabling custom prepare and submit function to overcome DMA limitation.
> > > >
> > > > In the Intel KeemBay solution, the DW AXI-based DMA has a
> > > > limitation on the number of DMA blocks per transfer. In the case
> > > > of 16 bit audio ASoC would allocate blocks exceeding the DMA block limitation.
> > >
> > > I'm still not sure the hardware has such a limitation.
> > >
> > > The Synopsys IP supports linked list (LLI) transfers and I hardly
> > > can imagine the list has any limitation. Even though, one can always
> > > emulate LLI in software how it's done in the DesignWare AHB DMA driver.
> > >
> > > I have briefly read chapter 4.6 "AXI_DMA" of Keem Bay TRM and didn't
> > > find any errata or limits like this.
> > [>>] Intel KeemBay datasheet can be found at below link:
> 
> ** Please wrap your replies to 80 chars ** I have reflown below
[>>] Noted.
> 
> 
> > https://www.intel.com/content/www/us/en/secure/design/confidential/pro
> > ducts-and-solutions/processors-and-chipsets/keem-bay/technical-library
> > .html?grouping=EMT_Content%20Type&sort=title:asc
> 
> And this link is not accessible freely!
[>>] Sorry, perhaps need to apply the access.
> 
> > Pg783, "Programmable transfer length (block length), max 1024".
> 
> Okay so block length cant be more than 1024, and IIUC that is 1024 items and not
> bytes right
[>>] Yes, it is 1024 items/blocks
> 
> > Sub-list can't exceed 1024 blocks.  BTW, I think the 16bits audio
> > could be a confusion because it is not about the number of bits, but
> > rather the constraint of the block length.
> > Base on my understanding,
> > Audio needs a period larger than 10ms, regardless of the bit depth.
> > The questions here are:
> > 1. Should DMAEngine expose a new API to constraint the block_length
> > (instead of size in bytes)?
> > 2. Should DMA client re-split the linked-list before passing the
> > linked-list to DMAEngine.
> > 3. Should DMA controller driver re-split the linked-list before
> > execution.
> 
> I would go with 3, this is not a fwk issue and can be easily handled in the dma driver.
> It knows the limitation on block and can split a period into multiple blocks and set
> the interrupt on last block. I do not see why that will not work
[>>] Got it. A separate patch shall be submitted to AxiDMA to split the linked-list. 
Hope the rest of folks are fine with this approach.
> 
> --
> ~Vinod