linux-kernel - Re: [RFC v02 00/15] dmaengine: New 'universal' API for requesting channel

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Date:	Wed, 2 Dec 2015 12:51:43 +0200
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmaengine <dmaengine@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	Sekhar Nori <nsekhar@...com>,
	linux-spi <linux-spi@...r.kernel.org>
Subject: Re: [RFC v02 00/15] dmaengine: New 'universal' API for requesting
 channel

On 12/01/2015 04:24 PM, Arnd Bergmann wrote:
> On Tuesday 01 December 2015 15:45:32 Peter Ujfalusi wrote:
>>>> static struct dma_filter_map da830_edma_map[] = {
>>>>         DMA_FILTER_ENTRY("davinci-mcasp.0", "rx", EDMA_CTLR_CHAN(0, 0)),
>>>>         DMA_FILTER_ENTRY("davinci-mcasp.0", "tx", EDMA_CTLR_CHAN(0, 1)),
>>>>         DMA_FILTER_ENTRY("davinci-mcasp.1", "rx", EDMA_CTLR_CHAN(0, 2)),
>>>>         DMA_FILTER_ENTRY("davinci-mcasp.1", "tx", EDMA_CTLR_CHAN(0, 3)),
>>>>         DMA_FILTER_ENTRY("davinci-mcasp.2", "rx", EDMA_CTLR_CHAN(0, 4)),
>>>>         DMA_FILTER_ENTRY("davinci-mcasp.2", "tx", EDMA_CTLR_CHAN(0, 5)),
>>>>         DMA_FILTER_ENTRY("spi_davinci.0", "rx", EDMA_CTLR_CHAN(0, 14)),
>>>>         DMA_FILTER_ENTRY("spi_davinci.0", "tx", EDMA_CTLR_CHAN(0, 15)),
>>>>         DMA_FILTER_ENTRY("da830-mmc.0", "rx", EDMA_CTLR_CHAN(0, 16)),
>>>>         DMA_FILTER_ENTRY("da830-mmc.0", "tx", EDMA_CTLR_CHAN(0, 17)),
>>>>         DMA_FILTER_ENTRY("spi_davinci.1", "rx", EDMA_CTLR_CHAN(0, 18)),
>>>>         DMA_FILTER_ENTRY("spi_davinci.1", "tx", EDMA_CTLR_CHAN(0, 19)),
>>>
>>> Does this ".2" and so prevent driver to use auto ID for platform devices?
>>
>> Yes, as all the infra around the traditional board files with platform_device
>> creation does. Ideally we could have 'phandle' pointing from this table to the
>> device in question (or other way around), but I'm not aware of anything we can
>> use.
> 
> I was thinking that we could use a pointer to the device structure, but
> if you have that, you can also just read the name from it.

Hrm to have pdev pointer instead of the devname string? In the core we could
get the pdev from the caller's device with to_platform_device(dev) and simply
compare the pointers...

One of the issue I see (in mach-davinci and mach-omap1/2) is that the pdevs
are scattered around in the c files so gathering the pointers to a place where
we can see them to be able to use it in the dma_filter_map is not going to be
light weight task.
Furthermore we have the omap_hwmod for OMAP2+ which creates the actual pdevs
and resources from the omap_hwmod data structures so getting out the DMA event
numbers there is not going to be easy either...

I'll hold back the RFC v3 to see if we should switch to pdev pointer or stay
with the devname strings here.

-- 
Péter
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