From: arnd@arndb•de (Arnd Bergmann)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] of: Add generic device tree DMA helpers
Date: Mon, 19 Mar 2012 14:06:34 +0000 [thread overview]
Message-ID: <201203191406.35064.arnd@arndb.de> (raw)
In-Reply-To: <4F6734DD.3020203@atmel.com>
On Monday 19 March 2012, Nicolas Ferre wrote:
> > This _xlate is nearly useless as a generic API. It solves the problem for
> > the specific case where the driver is hard-coded to know which DMA engine
> > to talk to, but since the returned data doesn't provide any context, it
> > isn't useful if there are multiple DMA controllers to choose from.
>
> You mean, if there is no DMA controller phandle specified in the
> property? I think that it is not the purpose of this API to choose a DMA
> controller, Nor to provide a channel. The only purpose of this API is to
> give a HW request to be used by a DMA slave driver. This slave should
> already have a channel to use and a controller to talk to.
I don't think there is consensus on this point. I would expect that
the device driver requests the channel with the same operation as
passing the request data.
Contrast the two ways this is done in atmel-mci.c and mmci.c:
==== atmel ====
/* interface between platform and driver */
struct at_dma_slave {
struct device *dma_dev;
dma_addr_t tx_reg;
dma_addr_t rx_reg;
enum at_dma_slave_width reg_width;
u32 cfg;
u32 ctrla;
};
struct mci_dma_data {
struct at_dma_slave sdata;
};
#define slave_data_ptr(s) (&(s)->sdata)
#define find_slave_dev(s) ((s)->sdata.dma_dev)
/* in atmel-mci.c */
static bool atmci_filter(struct dma_chan *chan, void *slave)
{
struct mci_dma_data *sl = slave;
if (sl && find_slave_dev(sl) == chan->device->dev) {
chan->private = slave_data_ptr(sl);
return true;
} else {
return false;
}
}
static bool atmci_configure_dma(struct atmel_mci *host)
{
...
host->dma.chan = dma_request_channel(mask, atmci_filter, pdata->dma_slave);
...
}
==== mmci ====
/* in drivers/dma/ste_dma40.c, others in pl330.c, coh901318.c, ... */
bool stedma40_filter(struct dma_chan *chan, void *data)
{
struct stedma40_chan_cfg *info = data;
struct d40_chan *d40c = container_of(chan, struct d40_chan, chan);
int err;
err = d40_validate_conf(d40c, info);
if (!err)
d40c->dma_cfg = *info;
d40c->configured = true;
return err == 0;
}
EXPORT_SYMBOL(stedma40_filter);
/* in mmci.h */
struct mmci_platform_data {
...
bool (*dma_filter)(struct dma_chan *chan, void *filter_param);
void *dma_rx_param;
void *dma_tx_param;
};
/* in mmci.c */
static void __devinit mmci_dma_setup(struct mmci_host *host)
{
...
host->dma_rx_channel = dma_request_channel(mask, plat->dma_filter, plat->dma_rx_param);
...
}
====
Whatever we come up with obviously needs to work with both drivers.
I think we will end up with something closer to the second one, except
that the dma parameters do not come from platform_data but from the
#dma-request property, which also identifies the controller and channel.
Arnd
next prev parent reply other threads:[~2012-03-19 14:06 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 17:29 [RFC PATCH 1/2] of: Add generic device tree DMA helpers Cousson, Benoit
2012-01-27 18:13 ` Stephen Warren
2012-01-27 20:36 ` Cousson, Benoit
2012-01-28 18:12 ` Grant Likely
2012-01-28 18:06 ` Grant Likely
2012-01-31 21:26 ` Cousson, Benoit
2012-02-02 4:52 ` Grant Likely
2012-01-31 23:09 ` Russell King - ARM Linux
2012-02-01 10:50 ` Cousson, Benoit
2012-02-02 8:45 ` Russell King - ARM Linux
2012-02-02 8:54 ` Cousson, Benoit
2012-02-22 10:59 ` Nicolas Ferre
2012-02-23 10:03 ` Cousson, Benoit
2012-02-23 15:51 ` Nicolas Ferre
2012-02-23 15:57 ` Cousson, Benoit
2012-02-27 13:09 ` Nicolas Ferre
2012-02-27 14:22 ` Cousson, Benoit
2012-02-27 17:28 ` Nicolas Ferre
2012-02-29 14:54 ` [RFC PATCH] of: DMA helpers: manage generic requests specification Nicolas Ferre
2012-02-29 20:54 ` Stephen Warren
2012-03-05 13:14 ` Cousson, Benoit
2012-03-05 18:30 ` Stephen Warren
2012-03-05 19:57 ` Russell King - ARM Linux
2012-03-05 10:55 ` Cousson, Benoit
2012-03-05 15:36 ` Grant Likely
2012-03-14 17:47 ` Nicolas Ferre
2012-03-14 18:16 ` Stephen Warren
2012-03-15 8:38 ` [PATCH] of: Add generic device tree DMA helpers Nicolas Ferre
2012-03-15 9:22 ` Arnd Bergmann
2012-03-15 9:26 ` Russell King - ARM Linux
2012-03-15 10:09 ` Arnd Bergmann
2012-03-17 9:42 ` Grant Likely
2012-03-17 16:03 ` Arnd Bergmann
2012-03-18 9:08 ` Grant Likely
2012-03-15 10:27 ` Thierry Reding
2012-03-17 10:47 ` Grant Likely
2012-03-18 9:22 ` Thierry Reding
2012-03-18 15:10 ` Arnd Bergmann
2012-03-18 18:22 ` Grant Likely
2012-03-19 13:02 ` Mark Brown
2012-03-19 15:01 ` Arnd Bergmann
2012-03-19 15:07 ` Stephen Warren
2012-03-19 15:45 ` Arnd Bergmann
2012-03-19 16:54 ` Stephen Warren
2012-03-15 16:30 ` Cousson, Benoit
2012-03-15 19:57 ` Russell King - ARM Linux
2012-03-15 20:41 ` Arnd Bergmann
2012-03-15 21:39 ` Cousson, Benoit
2012-03-15 21:55 ` Russell King - ARM Linux
2012-03-16 9:56 ` Arnd Bergmann
2012-03-20 14:02 ` Matt Porter
2012-03-15 23:45 ` Nicolas Pitre
2012-03-16 10:03 ` Arnd Bergmann
2012-03-16 11:19 ` Cousson, Benoit
2012-03-16 12:04 ` Arnd Bergmann
2012-03-16 13:28 ` Cousson, Benoit
2012-03-16 13:36 ` Nicolas Ferre
2012-03-17 9:40 ` Grant Likely
2012-03-18 20:13 ` Arnd Bergmann
2012-03-18 20:44 ` Grant Likely
2012-03-18 21:58 ` Arnd Bergmann
2012-03-18 22:12 ` Arnd Bergmann
2012-03-19 13:37 ` Nicolas Ferre
2012-03-19 15:20 ` Russell King - ARM Linux
2012-03-19 15:58 ` Cousson, Benoit
2012-03-19 13:30 ` Nicolas Ferre
2012-03-19 14:06 ` Arnd Bergmann [this message]
2012-03-19 15:33 ` Russell King - ARM Linux
2012-03-19 16:11 ` Arnd Bergmann
2012-03-19 18:06 ` Jassi Brar
2012-03-19 16:31 ` Nicolas Ferre
2012-03-19 17:49 ` Cousson, Benoit
2012-03-19 14:45 ` Grant Likely
2012-03-20 14:54 ` Nicolas Ferre
2012-03-20 10:13 ` [PATCH v2 1/2] " Nicolas Ferre
2012-03-20 10:13 ` [PATCH 2/2] of: selftest/dma: Add selftest for new DT DMA request helpers Nicolas Ferre
2012-03-20 14:16 ` Grant Likely
2012-03-20 10:17 ` [PATCH] of: dma/fixup Nicolas Ferre
2012-03-20 13:03 ` [PATCH v2 1/2] of: Add generic device tree DMA helpers Arnd Bergmann
2012-03-20 15:38 ` Stephen Warren
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