linux-kernel - Re: [PATCH 3/4] dmaengine: core: Introduce new, universal API to request a channel

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Message-ID: <CAHp75VdeZBuxTd1rCFDLf9iXuhPidOejF-Ki=nqAqAvSmx99xA@mail.gmail.com>
Date:	Thu, 3 Dec 2015 18:30:04 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	Vinod Koul <vinod.koul@...el.com>, Arnd Bergmann <arnd@...db.de>,
	"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>,
	Sekhar Nori <nsekhar@...com>, Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH 3/4] dmaengine: core: Introduce new, universal API to
 request a channel

On Thu, Dec 3, 2015 at 4:33 PM, Peter Ujfalusi <peter.ujfalusi@...com> wrote:
> The two API function can cover most, if not all current APIs used to
> request a channel. With minimal effort dmaengine drivers, platforms and
> dmaengine user drivers can be converted to use the two function.
>
> struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask);
>
> To request any channel matching with the requested capabilities, can be
> used to request channel for memcpy, memset, xor, etc where no hardware
> synchronization is needed.
>
> struct dma_chan *dma_request_chan(struct device *dev, const char *name);
> To request a slave channel. The dma_request_chan() will try to find the
> channel via DT, ACPI or in case if the kernel booted in non DT/ACPI mode
> it will use a filter lookup table and retrieves the needed information from
> the dma_slave_map provided by the DMA drivers.
> This legacy mode needs changes in platform code, in dmaengine drivers and
> finally the dmaengine user drivers can be converted:
>
> For each dmaengine driver an array of DMA device, slave and the parameter
> for the filter function needs to be added:
>
> static const struct dma_slave_map da830_edma_map[] = {
>         { "davinci-mcasp.0", "rx", EDMA_FILTER_PARAM(0, 0) },
>         { "davinci-mcasp.0", "tx", EDMA_FILTER_PARAM(0, 1) },
>         { "davinci-mcasp.1", "rx", EDMA_FILTER_PARAM(0, 2) },
>         { "davinci-mcasp.1", "tx", EDMA_FILTER_PARAM(0, 3) },
>         { "davinci-mcasp.2", "rx", EDMA_FILTER_PARAM(0, 4) },
>         { "davinci-mcasp.2", "tx", EDMA_FILTER_PARAM(0, 5) },
>         { "spi_davinci.0", "rx", EDMA_FILTER_PARAM(0, 14) },
>         { "spi_davinci.0", "tx", EDMA_FILTER_PARAM(0, 15) },
>         { "da830-mmc.0", "rx", EDMA_FILTER_PARAM(0, 16) },
>         { "da830-mmc.0", "tx", EDMA_FILTER_PARAM(0, 17) },
>         { "spi_davinci.1", "rx", EDMA_FILTER_PARAM(0, 18) },
>         { "spi_davinci.1", "tx", EDMA_FILTER_PARAM(0, 19) },
> };
>
> This information is going to be needed by the dmaengine driver, so
> modification to the platform_data is needed, and the driver map should be
> added to the pdata of the DMA driver:
>
> da8xx_edma0_pdata.slave_map = da830_edma_map;
> da8xx_edma0_pdata.slavecnt = ARRAY_SIZE(da830_edma_map);
>
> The DMA driver then needs to configure the needed device -> filter_fn
> mapping before it registers with dma_async_device_register() :
>
> if (info->slave_map) {
>         ecc->dma_slave.filter_map.map = info->slave_map;
>         ecc->dma_slave.filter_map.mapcnt = info->slavecnt;
>         ecc->dma_slave.filter_map.filter_fn = edma_filter_fn;

One nitpick here.

I think filter_map.filter_fn naming is duplicate.

What about

dma_device
  .filter -> filter data (or .filter_data)
    .map -> mappings
    .map_count -> # of entries in mappings
    .fn -> filter function

What do you think?

> }
>
> When neither DT or ACPI lookup is available the dma_request_chan() will
> try to match the requester's device name with the filter_map's list of
> device names, when a match found it will use the information from the
> dma_slave_map to get the channel with the dma_get_channel() internal
> function.


-- 
With Best Regards,
Andy Shevchenko
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