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

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Date:	Mon, 23 May 2016 13:30:18 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Felipe Balbi <balbi@...nel.org>, Tony Lindgren <tony@...mide.com>,
	Peter Ujfalusi <peter.ujfalusi@...com>
CC:	<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>, <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 Felipe,

On Monday 23 May 2016 12:48 PM, Felipe Balbi wrote:
> 
> Hi Kishon,
> 
> Kishon Vijay Abraham I <kishon@...com> writes:
>> Hi Felipe,
>>
>> On Friday 20 May 2016 12:06 AM, Felipe Balbi wrote:
>>>
>>> Hi,
>>>
>>> Tony Lindgren <tony@...mide.com> writes:
>>>> * Peter Ujfalusi <peter.ujfalusi@...com> [160519 01:10]:
>>>>> On 05/18/2016 10:30 PM, Tony Lindgren wrote:
>>>>>> Ideally the adma support would be a separate loadable module,
>>>>>> similar how the cppi41dma is a child of the OTG controller.
>>>>>
>>>>> The Master DMA is part of the hsmmc IP block. If the same ADMA module is
>>>>> present on other IPs it might be beneficial to have a helper library to handle
>>>>> it (allocating the descriptor pool, wrinting, updating descriptors, etc).
>>>>
>>>> OK. Yeah if it's part of the MMC controller it makes no sense to
>>>> separate it. So then the conecrns are using alternate DMA
>>>> implementations and keeping PM runtime working :)
>>>>
>>>> BTW, Felipe mentioned that the best thing to do in the long run would
>>>> be to set up sdhci-omap.c operating in ADMA mode.
>>>>
>>>> Felipe, care to summarize what you had in mind?
>>>
>>> yeah, just write a new sdhci-omap.c to start moving away from
>>> omap-hsmmc.c, just like it was done for 8250-omap.
>>>
>>> At the beginning, it could be just the bare minimum to get it working
>>> and slowly move over stuff like pm runtime, dmaengine, PIO. Move more
>>> platforms over to that driver and, eventually, get rid of omap-hsmmc.c
>>> altogether.
>>>
>>> That way, development can be focussed on generic layers (SDHCI) to which
>>> OMAP MMC controller is compliant (apart from the VERSION register
>>> quirk).
>>
>> About an year back, when I tried using SDHCI for OMAP I ran into
>> issues and was not able to get it working. IIRC SDHCI_PRESENT_STATE
>> (or OMAP_HSMMC_PSTATE) was not showing the correct state for card
>> present and is unable to raise an interrupt when a card is inserted. I
>> didn't debug this further.
> 
> I'd say this is a bug in hsmmc. I remember seeing some bits in some
> TI-specific register (before SDHCI address space starts) which can be
> used to keep parts of SDHCI powered on exactly so normal WP and CD pins
> work as expected.
> 
> In any case, adding support for GPIO-based card detect to generic SDHCI
> shouldn't be too difficult :-)
> 
>> It also kept me wondering why gpio interrupt was always used for card
>> detect instead of using mmci_sdcd line of the controller.
> 
> Probably a really, really old bug which nobody ever debugged properly ;-)
> 
> ps: you don't need that ADMA2 DT property, btw. There's a bit in another
> register which you can check if $this controller was configured with
> ADMA2 support or not. IIRC, OMAP5's TRM describes them.

hmm yeah.. Should be the MADMA_EN in MMCHS_HL_HWINFO.

Thanks
Kishon