linux-kernel - Re: [PATCH] dmaengine: ti: omap-dma: Configure LCH

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Date:   Tue, 20 Nov 2018 23:04:06 +0200
From:   Aaro Koskinen <aaro.koskinen@....fi>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     vkoul@...nel.org, dan.j.williams@...el.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        tony@...mide.com, linux-omap@...r.kernel.org,
        rmk+kernel@...linux.org.uk
Subject: Re: [PATCH] dmaengine: ti: omap-dma: Configure LCH_TYPE for OMAP1

Hi,

On Tue, Nov 20, 2018 at 09:28:37AM +0200, Peter Ujfalusi wrote:
> On 19/11/2018 20.46, Aaro Koskinen wrote:
> > On Mon, Nov 19, 2018 at 12:40:40PM +0200, Peter Ujfalusi wrote:
> >> When the channel is configured for slave operation the LCH_TYPE needs to be
> >> set to LCh-P. For memcpy channels the LCH_TYPE must be set to LCh-2D.
> >>
> >> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> > 
> > I don't have the documentation, but based on what omap_udc driver (still
> > using the legacy OMAP DMA API) does this seems to be correct.
> 
> They are hard to fine, true. From the omap1710 TRM:
> 
> Logical channel types (LCh types) supported are:
> - LCh-2D for nonsynchronized transfers (memory transfers, 1D and 2D)
> - LCh-P for synchronized transfers (mostly peripheral transfers)
> - LCh-PD similar to LCh-P but runs on a dedicated physical channel
> - LCh-G for graphical transfers/operations
> - LCh-D for display transfers

(I found a public document "OMAP5912 Multimedia Processor Direct
Memory Access (DMA) Support Reference Guide", documenting these; easy
to confuse with "OMAP5910 Dual-Core Processor System DMA Controller
Reference Guide".)

> Looking at other part it looks like hat LCH-2D channel mode can happily
> service a peripheral. LCH-P supports the same features as LCH-2D, but it
> lacks support for Single/Double-indexed addressing mode on the
> peripheral port side.
> 
> So, this patch might not be needed at all. Can you test the omap_udc
> with s/OMAP_DMA_LCH_P/OMAP_DMA_LCH_2D
> 
> If USB works, then we can just drop this patch.

Unfortunately omap_udc does not seem to work at all anymore with DMA on
my 770 setup. :-(

I had switched to PIO mode in 2015 since the WARNs about legacy DMA
API were too annoying and flooding the console. And now that I tried
using DMA again with g_ether, it doesn't work anymore. The device get's
recognized on host side, but no traffic goes through. Switching back to
PIO makes it to work again.

A.