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

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Date:   Tue, 18 Dec 2018 12:11:06 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Aaro Koskinen <aaro.koskinen@....fi>,
        Russell King - ARM Linux <linux@...linux.org.uk>
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 17/12/2018 21.16, Aaro Koskinen wrote:
> 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

In omap1510 it is 4 x data_type
In omap1610/1710 it is 4 x data_type (only data_type == 32bit is supported)
>From omap2420+ 32 bytes (8x32bit/4x64bit)

So for OMAP1 we need to have different handling of the burst:
only enable if data_type is 32bit.

> 	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.
> 

- Péter

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