Subject: [RFC v03 03/15] dmaengine: core: Introduce new, universal API to request a channel

From: [email-masked] (Peter Ujfalusi)
Date: Thu, 3 Dec 2015 12:34:00 +0200

On 12/02/2015 04:35 PM, Andy Shevchenko wrote:
>> +const static struct dma_filter_map *dma_filter_match(struct dma_device *device,
>> +                                              const char *name,
>> +                                              struct device *dev)
>> +{
>> +       const struct dma_filter_map *map_found = NULL;
>> +       int i;
>> +
>> +       if (!device->filter_map.mapcnt)
>> +               return NULL;
>> +
>> +       for (i = 0; i < device->filter_map.mapcnt; i++) {
>> +               const struct dma_filter_map *map = &device->filter_map.map[i];
>> +
>> +               if (!strcmp(map->devname, dev_name(dev)) &&
>> +                   !strcmp(map->slave, name)) {
>> +                       map_found = map;
>> +                       break;
> 
> return map?
> 
>> +               }
>> +       }
>> +
> 
> return NULL;

OK.

> 
>> +       return map_found;
>> +}
>> +
>> +/**
>> + * dma_request_chan - try to allocate an exclusive slave channel
>> + * @dev:       pointer to client device structure
>> + * @name:      slave channel name
>> + *
>> + * Returns pointer to appropriate DMA channel on success or an error pointer.
>> + */
>> +struct dma_chan *dma_request_chan(struct device *dev, const char *name)
>> +{
>> +       struct dma_device *device, *_d;
> 
> If you name *d, *_d; it would?
> 
>> +       struct dma_chan *chan = NULL;
>> +
> 
>> +       /* If device-tree is present get slave info from here */
>> +       if (dev->of_node)
>> +               chan = of_dma_request_slave_channel(dev->of_node, name);
>> +
>> +       /* If device was enumerated by ACPI get slave info from here */
>> +       if (has_acpi_companion(dev) && !chan)
>> +               chan = acpi_dma_request_slave_chan_by_name(dev, name);
> 
> This part might be a good candidate to be moved to
> drivers/base/property.c as
> struct dma_chan *device_property_dma_request_chan(?) or alike.

Not sure if it is a good idea. We want users to use the dmaengine API for
requesting DMA channels, but if we just add renamed
dma_request_slave_channel_reason() - essentially the
device_property_dma_request_chan() would be the same - what users will stop to
use some random API to request the channel?
I'm not really sure if something which is returning 'struct dma_chan *' can be
considered as property to anything. The DMA request number can be seen as a
property for a given device, but a dmaengine related pointer?

Actually I was thinking to move the declaration for these from
include/linux/of_dma.h/acpi_dma.h to a header under drivers/dma/

Also move as much local to dmaengine as it is possible to have cleaner
interface towards the client drivers.

> 
>> +
>> +       if (chan) {
>> +               /* Valid channel found */
>> +               if (!IS_ERR(chan))
>> +                       return chan;
>> +
> 
> They might return EPROBE_DEFER. Is any specific handling needed here?

-EPROBE_DEFER means that the DMA driver is not yet loaded and in this case the
lookup for the filter function would also fail, but we have additional and
needless warning printed out. It is better to return with the deferred code also.

> 
>> +               pr_warn("%s: %s DMA request failed, falling back to legacy\n",
>> +                       __func__, dev->of_node ? "OF" : "ACPI");
>> +       }
>> +
>> +       /* Try to find the channel via the DMA filter map(s) */
>> +       mutex_lock(&dma_list_mutex);
>> +       list_for_each_entry_safe(device, _d, &dma_device_list, global_node) {
>> +               dma_cap_mask_t mask;
>> +               const struct dma_filter_map *map = dma_filter_match(device,
>> +                                                                   name, dev);
>> +
>> +               if (!map)
>> +                       continue;
>> +
>> +               dma_cap_zero(mask);
>> +               dma_cap_set(DMA_SLAVE, mask);
>> +
>> +               chan = find_candidate(device, &mask,
>> +                                     device->filter_map.filter_fn, map->param);
> 
> ?allow to put this on single line I believe.

if not in one line, but will look much better.

> 
>> +               if (!IS_ERR(chan))
>> +                       break;
>> +       }
>> +       mutex_unlock(&dma_list_mutex);
>> +
>> +       return chan ? chan : ERR_PTR(-EPROBE_DEFER);
>> +}
>> +EXPORT_SYMBOL_GPL(dma_request_chan);
>> +
>> +/**
>> + * dma_request_chan_by_mask - allocate a channel satisfying certain capabilities
>> + * @mask: capabilities that the channel must satisfy
>> + *
>> + * Returns pointer to appropriate DMA channel on success or an error pointer.
>> + */
>> +struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask)
>> +{
>> +       struct dma_chan *chan;
>> +
>> +       if (!mask)
>> +               return ERR_PTR(-ENODEV);
>> +
>> +       chan = __dma_request_channel(mask, NULL, NULL);
>> +       if (!chan)
>> +               chan = ERR_PTR(-ENODEV);
>> +
>> +       return chan;
>> +}
>> +EXPORT_SYMBOL_GPL(dma_request_chan_by_mask);
>> +
>>  void dma_release_channel(struct dma_chan *chan)
>>  {
>>         mutex_lock(&dma_list_mutex);
>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
>> index a2b7c2071cf4..49d48e69c179 100644
>> --- a/include/linux/dmaengine.h
>> +++ b/include/linux/dmaengine.h
>> @@ -606,6 +606,18 @@ enum dmaengine_alignment {
>>         DMAENGINE_ALIGN_64_BYTES = 6,
>>  };
>>
>> +struct dma_filter_map {
>> +        char *devname;
> 
> const ?
> 
>> +        char *slave;
> 
> Ditto.

Sure.
I'm also going to change the name of the struct to dma_slave_map

> 
>> +        void *param;
>> +};
>> +
>> +struct dma_filter {
>> +        dma_filter_fn filter_fn;
>> +        int mapcnt;
>> +        const struct dma_filter_map *map;
>> +};
> 
> 

-- 
P?ter