linux-kernel - Re: [RFC PATCH 2/3] mmc: host: omap

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Date:	Thu, 19 May 2016 11:36:18 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-mmc@...r.kernel.org>, <afenkart@...il.com>,
	<ulf.hansson@...aro.org>, <linux@...linux.org.uk>,
	<tony@...mide.com>
CC:	<rogerq@...com>, <bcousson@...libre.com>, <galak@...eaurora.org>,
	<ijc+devicetree@...lion.org.uk>, <mark.rutland@....com>,
	<pawel.moll@....com>, <robh+dt@...nel.org>, <nsekhar@...com>
Subject: Re: [RFC PATCH 2/3] mmc: host: omap_hsmmc: Enable ADMA2

Hi Peter,

On Wednesday 18 May 2016 03:54 PM, Peter Ujfalusi wrote:
> On 05/18/16 11:45, Kishon Vijay Abraham I wrote:
>> omap hsmmc host controller has ADMA2 feature. Enable it here
>> for better read and write throughput. Add a new dt binding
>> "ti,use_adma" to enable ADMA2.
>>
>> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
>> ---
>>  .../devicetree/bindings/mmc/ti-omap-hsmmc.txt      |    1 +
>>  drivers/mmc/host/omap_hsmmc.c                      |  320 ++++++++++++++++----
>>  include/linux/platform_data/hsmmc-omap.h           |    1 +
>>  3 files changed, 256 insertions(+), 66 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/mmc/ti-omap-hsmmc.txt b/Documentation/devicetree/bindings/mmc/ti-omap-hsmmc.txt
>> index 74166a0..eb5ceec2 100644
>> --- a/Documentation/devicetree/bindings/mmc/ti-omap-hsmmc.txt
>> +++ b/Documentation/devicetree/bindings/mmc/ti-omap-hsmmc.txt
>> @@ -28,6 +28,7 @@ specifier is required.
>>  dma-names: List of DMA request names. These strings correspond
>>  1:1 with the DMA specifiers listed in dmas. The string naming is
>>  to be "rx" and "tx" for RX and TX DMA requests, respectively.
>> +ti,use_adma: enable adma2 feature
> 
> Do we have use case when you want to fall back to generic DMA instead of aDMA2?
> IMHO if the driver supports aDMA2, it is going to use it instead of the
> generic s/eDMA.
> What I mean is:
> the driver implements the aDMA2 support.
> if the IP has support for aDMA2, then it is going to use it, otherwise it will
> use the generic DMA.

hmm.. how will the driver know if the IP has support for aDMA2. Using dt
binding is one way. Using MMCHS_HL_HWINFO is another way but then the register
offsets in omap_hsmmc driver has to be modified for omap4+.

Thanks
Kishon