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

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Message-ID: <20181217191657.GB7288@darkstar.musicnaut.iki.fi>
Date:   Mon, 17 Dec 2018 21:16:58 +0200
From:   Aaro Koskinen <aaro.koskinen@....fi>
To:     Russell King - ARM Linux <linux@...linux.org.uk>,
        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
Subject: Re: [PATCH] dmaengine: ti: omap-dma: Configure LCH_TYPE for OMAP1

On Thu, Nov 22, 2018 at 03:12:36PM +0000, Russell King - ARM Linux wrote:
> Also we can't deal with the omap_set_dma_dest_burst_mode() setting -
> DMAengine always uses a 64 byte burst, but udc wants a smaller burst
> setting.  Does this matter?

Looking at OMAP1 docs, it seems it supports only 16 bytes. Then checking
DMAengine code, I don't think these CSDP bit values are not valid
for OMAP1:

        CSDP_SRC_BURST_1        = 0 << 7,
        CSDP_SRC_BURST_16       = 1 << 7,
        CSDP_SRC_BURST_32       = 2 << 7,
        CSDP_SRC_BURST_64       = 3 << 7,

>From TI SPRU674 document, pages 50-51:

	0	single access (no burst)
	1	single access (no burst)
	2	burst 4
	3	reserved (do not use this setting)

So if CSDP_SRC_BURST_64 (3) gets programmed OMAP1, I wonder what is the
end result, no burst or burst 4...

A.