[PATCH V3] dma: add channel request API that supports deferred probe

[Shevchenko, Andriy]

On Mon, 2013-11-25 at 14:47 -0700, Stephen Warren wrote:
> From: Stephen Warren <swarren at nvidia.com>
> 
> dma_request_slave_channel() simply returns NULL whenever DMA channel
> lookup fails. Lookup could fail for two distinct reasons:
> 
> a) No DMA specification exists for the channel name.
>    This includes situations where no DMA specifications exist at all, or
>    other general lookup problems.
> 
> b) A DMA specification does exist, yet the driver for that channel is not
>    yet registered.
> 
> Case (b) should trigger deferred probe in client drivers. However, since
> they have no way to differentiate the two situations, it cannot.
> 
> Implement new function dma_request_slave_channel_or_err(), which performs
> identically to dma_request_slave_channel(), except that it returns an
> error-pointer rather than NULL, which allows callers to detect when
> deferred probe should occur.
> 
> Eventually, all drivers should be converted to this new API, the old API
> removed, and the new API renamed to the more desirable name. This patch
> doesn't convert the existing API and all drivers in one go, since some
> drivers call dma_request_slave_channel() then dma_request_channel() if
> that fails. That would require either modifying dma_request_channel() in
> the same way, or adding extra error-handling code to all affected
> drivers, and there are close to 100 drivers using the other API, rather
> than just the 15-20 or so that use dma_request_slave_channel(), which
> might be tenable in a single patch.
> 
> acpi_dma_request_slave_chan_by_name() doesn't currently implement
> deferred probe. It should, but this will be addressed later.

Couple of comments below.

[]

> --- a/drivers/dma/of-dma.c
> +++ b/drivers/dma/of-dma.c

[]

> @@ -152,17 +152,18 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  	struct of_dma		*ofdma;
>  	struct dma_chan		*chan;
>  	int			count, i;
> +	int			ret_no_channel = -ENODEV;

Could we re-use chan for the error as well?

>  	if (!np || !name) {
>  		pr_err("%s: not enough information provided\n", __func__);
> -		return NULL;
> +		return ERR_PTR(-ENODEV);
>  	}
>  
>  	count = of_property_count_strings(np, "dma-names");
>  	if (count < 0) {
>  		pr_err("%s: dma-names property of node '%s' missing or empty\n",
>  			__func__, np->full_name);
> -		return NULL;
> +		return ERR_PTR(-ENODEV);
>  	}
>  
>  	for (i = 0; i < count; i++) {
> @@ -174,8 +175,10 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  
>  		if (ofdma)

if (ofdma) {
...

>  			chan = ofdma->of_dma_xlate(&dma_spec, ofdma);
> -		else
> +		else {

} else {

to keep style.

> +			ret_no_channel = -EPROBE_DEFER;
>  			chan = NULL;
> +		}
>  
>  		mutex_unlock(&of_dma_lock);
>  
> @@ -185,7 +188,7 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  			return chan;
>  	}
>  
> -	return NULL;
> +	return ERR_PTR(ret_no_channel);
>  }


-- 
Andy Shevchenko <andriy.shevchenko at intel.com>
Intel Finland Oy
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