On Thursday 13 September 2012, Jon Hunter wrote:
> This is based upon the work by Benoit Cousson [1] and Nicolas Ferre [2]
> to add some basic helpers to retrieve a DMA controller device_node and the
> DMA request/channel information.
I think we're getting very close now, I only have a few small comments left
that should all be uncontroversial.
> +
> +Client drivers should specify the DMA property using a phandle to the controller
> +followed by DMA controller specific data.
> +
> +Required property:
> +- dmas: List of one or more DMA specifiers, each consisting of
> + - A phandle pointing to DMA controller node
> + - A single integer cell containing DMA controller
> + specific information. This typically contains a dma
> + request line number or a channel number, but can
> + contain any data that is used required for configuring
> + a channel.
> +- dma-names: Contains one identifier string for each dma specifier in
> + the dmas property. The specific strings that can be used
> + are defined in the binding of the DMA client device.
I think here we need to clarify that listing the same name multiple times implies
having multiple alternatives for the same channel.
> +Example:
> +
> +- One DMA write channel, one DMA read/write channel:
> +
> + i2c1: i2c@1 {
> + ...
> + dmas = <&sdma 2 /* read channel */
> + &sdma 3>; /* write channel */
> + dma-names = "rx", "tx"
> + ...
> + };
And please add an example documenting this case.
> +/**
> + * of_dma_find_channel - Find a DMA channel by name
> + * @np: device node to look for DMA channels
> + * @name: name of desired channel
> + * @dma_spec: pointer to DMA specifier as found in the device tree
> + *
> + * Find a DMA channel by the name. Returns 0 on success or appropriate
> + * errno value on error.
> + */
> +static int of_dma_find_channel(struct device_node *np, char *name,
> + struct of_phandle_args *dma_spec)
> +{
> + int count, i;
> + const char *s;
> +
> + count = of_property_count_strings(np, "dma-names");
> + if (count < 0)
> + return count;
> +
> + for (i = 0; i < count; i++) {
> + of_property_read_string_index(np, "dma-names", i, &s);
> +
> + if (strcmp(name, s))
> + continue;
> +
> + return of_parse_phandle_with_args(np, "dmas", "#dma-cells",
> + i, dma_spec);
> + }
> +
> + return -ENODEV;
> +}
I think we should at least keep trying the other channels with the same name when
of_parse_phandle_with_args fails. We might want to do something smarter in
the long run, e.g. to spread channel allocations across the avaialable controllers.
> +/**
> + * of_dma_request_slave_channel - Get the DMA slave channel
> + * @np: device node to get DMA request from
> + * @name: name of desired channel
> + *
> + * Returns pointer to appropriate dma channel on success or NULL on error.
> + */
> +struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
> + char *name)
> +{
> ...
> +}
> +EXPORT_SYMBOL_GPL(of_dma_request_slave_channel);
I think this no longer needs to be exported, with patch 2 on top.
> +/**
> + * of_dma_simple_xlate - Simple DMA engine translation function
> + * @dma_spec: pointer to DMA specifier as found in the device tree
> + * @of_dma: pointer to DMA controller data
> + *
> + * A simple translation function for devices that use a 32-bit value for the
> + * filter_param when calling the DMA engine dma_request_channel() function.
> + * Note that this translation function requires that #dma-cells is equal to 1
> + * and the argument of the dma specifier is the 32-bit filter_param. Returns
> + * pointer to appropriate dma channel on success or NULL on error.
> + */
> +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;
> +
> + if (!info || !info->filter_fn)
> + return NULL;
> +
> + if (count != 1)
> + return NULL;
> +
> + return dma_request_channel(info->dma_cap, info->filter_fn,
> + &dma_spec->args[0]);
> +}
But this one does.
Arnd
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