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Date: Wed, 15 May 2013 16:52:03 +0200
From: Lars-Peter Clausen <lars@...afoo.de>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC: linux-kernel@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
Dan Williams <djbw@...com>,
Russell King <rmk+kernel@....linux.org.uk>,
Peter Ujfalusi <peter.ujfalusi@...com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC/PATCH] dma: of: Make of_dma_simple_xlate match on DMA device
and channel ID
On 05/15/2013 03:55 PM, Laurent Pinchart wrote:
> Hi Lars-Peter,
>
> (CC'ing LAKML, I had forgotten to do so when I sent the patch)
>
> On Wednesday 15 May 2013 15:39:09 Lars-Peter Clausen wrote:
>> On 05/15/2013 03:27 PM, Laurent Pinchart wrote:
>>> When translating a DT DMA channel specifier, the most common use case is
>>> to match the DMA channel based on the channel DMA engine and channel ID.
>>> Modify the of_dma_simple_xlate() function to do so, simplifying the API
>>> for DMA engine drivers.
>>>
>>> There is no need to check the DMA cells count in the filter function as
>>> the check is already performed by the caller in of_dma_get_controller().
>>>
>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>>
>> Hi,
>>
>> I've submitted a very similar patch some time ago, see
>> https://lkml.org/lkml/2013/3/25/250
>
> Thanks. So my patch makes at least some sense :-)
>
> I had the impression that this is what omap-dma needs as well, hence the
> modification to the existing xlate function. I'm fine with a separate function
> as well if the current code covers different use cases.
My first attempt was to modify simple_xlate function, but I think it didn't
work for all users (some of which aren't applied yet), so I added a separate
function.
>
>>> ---
>>>
>>> drivers/dma/of-dma.c | 39 +++++++++++++++++++++++++++++++--------
>>> drivers/dma/omap-dma.c | 8 +-------
>>> include/linux/of_dma.h | 5 -----
>>> 3 files changed, 32 insertions(+), 20 deletions(-)
>>>
>>> I've implemented this function while working on a DMA engine driver, and
>>> realized that it wasn't specific to my driver at all. As I'm new to the
>>> DMA engine API, I'd appreciate feedback on whether this change makes
>>> sense, or if I should instead keep the existing of_dma_simple_xlate()
>>> function and create a separate simple xlate helper.
>>>
>>> diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
>>> index 7aa0864..702a45d 100644
>>> --- a/drivers/dma/of-dma.c
>>> +++ b/drivers/dma/of-dma.c
>>> @@ -202,6 +202,27 @@ struct dma_chan *of_dma_request_slave_channel(struct
>>> device_node *np,
>>> return NULL;
>>> }
>>>
>>> +struct of_dma_filter_args {
>>> + struct dma_device *device;
>>> + unsigned int chan_id;
>>> +};
>>> +
>>> +/**
>>> + * of_dma_simple_xlate_filter - Channel filter function for
>>> of_dma_simple_xlate + * @dma_chan: pointer to candidate DMA channel
>>> + * @param: pointer to filter parameter
>>> + *
>>> + * Filter out candidate DMA channels that don't match the channel ID or
>>> + * DMA engine device passed as arguments.
>>> + */
>>> +static bool of_dma_simple_xlate_filter(struct dma_chan *chan, void
>>> *param)
>>> +{
>>> + struct of_dma_filter_args *fargs = param;
>>> +
>>> + return (chan->device == fargs->device) &&
>>> + (chan->chan_id == fargs->chan_id);
>>> +}
>>> +
>>> /**
>>> * of_dma_simple_xlate - Simple DMA engine translation function
>>> * @dma_spec: pointer to DMA specifier as found in the device tree
>>> @@ -216,16 +237,18 @@ struct dma_chan *of_dma_request_slave_channel(struct
>>> device_node *np,>
>>> struct dma_chan *of_dma_simple_xlate(struct of_phandle_args *dma_spec,
>>> struct of_dma *ofdma)
>>> {
>>> - int count = dma_spec->args_count;
>>> - struct of_dma_filter_info *info = ofdma->of_dma_data;
>>> + struct dma_device *dev = ofdma->of_dma_data;
>>> + struct of_dma_filter_args fargs;
>>> + dma_cap_mask_t cap;
>>>
>>> - if (!info || !info->filter_fn)
>>> - return NULL;
>>> + /* There's no need to specify matching caps as we're going to match a
>>> + * specific DMA channel anyway.
>>> + */
>>> + dma_cap_zero(cap);
>>>
>>> - if (count != 1)
>>> - return NULL;
>>> + fargs.device = dev;
>>> + fargs.chan_id = dma_spec->args[0];
>>>
>>> - return dma_request_channel(info->dma_cap, info->filter_fn,
>>> - &dma_spec->args[0]);
>>> + return dma_request_channel(cap, of_dma_simple_xlate_filter, &fargs);
>>> }
>>> EXPORT_SYMBOL_GPL(of_dma_simple_xlate);
>>> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
>>> index ec3fc4f..7e7ff06 100644
>>> --- a/drivers/dma/omap-dma.c
>>> +++ b/drivers/dma/omap-dma.c
>>> @@ -69,10 +69,6 @@ static const unsigned es_bytes[] = {
>>> [OMAP_DMA_DATA_TYPE_S32] = 4,
>>> };
>>>
>>> -static struct of_dma_filter_info omap_dma_info = {
>>> - .filter_fn = omap_dma_filter_fn,
>>> -};
>>> -
>>> static inline struct omap_dmadev *to_omap_dma_dev(struct dma_device *d)
>>> {
>>> return container_of(d, struct omap_dmadev, ddev);
>>> @@ -641,11 +637,9 @@ static int omap_dma_probe(struct platform_device
>>> *pdev)>
>>> platform_set_drvdata(pdev, od);
>>> if (pdev->dev.of_node) {
>>> - omap_dma_info.dma_cap = od->ddev.cap_mask;
>>> -
>>> /* Device-tree DMA controller registration */
>>> rc = of_dma_controller_register(pdev->dev.of_node,
>>> - of_dma_simple_xlate, &omap_dma_info);
>>> + of_dma_simple_xlate, &od->ddev);
>>> if (rc) {
>>> pr_warn("OMAP-DMA: failed to register DMA controller\n");
>>> dma_async_device_unregister(&od->ddev);
>>> diff --git a/include/linux/of_dma.h b/include/linux/of_dma.h
>>> index 364dda7..3c0d9ac 100644
>>> --- a/include/linux/of_dma.h
>>> +++ b/include/linux/of_dma.h
>>> @@ -27,11 +27,6 @@ struct of_dma {
>>> void *of_dma_data;
>>> };
>>>
>>> -struct of_dma_filter_info {
>>> - dma_cap_mask_t dma_cap;
>>> - dma_filter_fn filter_fn;
>>> -};
>>> -
>>>
>>> #ifdef CONFIG_OF
>>> extern int of_dma_controller_register(struct device_node *np,
>>> struct dma_chan *(*of_dma_xlate)
--
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