Re: [RFC PATCH 2/3] mmc: host: omap_hsmmc: Enable ADMA2

From: Kishon Vijay Abraham I <kishon@ti.com>
To: Tony Lindgren <tony@atomide.com>, Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: <linux-kernel@vger.kernel.org>, <linux-omap@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-mmc@vger.kernel.org>, <afenkart@gmail.com>,
	<ulf.hansson@linaro.org>, <linux@armlinux.org.uk>,
	<rogerq@ti.com>, <bcousson@baylibre.com>, <galak@codeaurora.org>,
	<ijc+devicetree@hellion.org.uk>, <mark.rutland@arm.com>,
	<pawel.moll@arm.com>, <robh+dt@kernel.org>, <nsekhar@ti.com>
Subject: Re: [RFC PATCH 2/3] mmc: host: omap_hsmmc: Enable ADMA2
Date: Thu, 19 May 2016 11:44:16 +0530	[thread overview]
Message-ID: <573D59B8.7050701@ti.com> (raw)
In-Reply-To: <20160518193028.GT5995@atomide.com>

Hi Tony,

On Thursday 19 May 2016 01:00 AM, Tony Lindgren wrote:
> * Peter Ujfalusi <peter.ujfalusi@ti.com> [160518 03:26]:
>> 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@ti.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?
> 
> Yes my guess is that PM runtime breaks with these currently..

pm_runtime_get is invoked during omap_hsmmc_request and pm_runtime_put is
invoked during omap_hsmmc_request_done. Both these calls are outside DMA API's.
So it shouldn't break anything w.r.t PM runtime no?
> 
>> 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.
> 
> Ideally the adma support would be a separate loadable module,
> similar how the cppi41dma is a child of the OTG controller.
> 
> That way the systems wanting to use adma can just specify it
> in the binding, and adma PM runtime support can be added later
> on.
> 
> Of course this won't work if the adma registers are sprinkled
> within the MMC controller registers..

right, adma registers are within the MMC controller register space.

Thanks
Kishon