On Sat, Mar 30, 2013 at 02:05:43AM +0530, Vinod Koul wrote:
> On Wed, Mar 27, 2013 at 10:57:57AM +0200, Andy Shevchenko wrote:
> > + * @dev: struct device to get DMA request from
> > + * @index: index of FixedDMA descriptor for @dev
> > + *
> > + * Returns pointer to appropriate dma channel on success or NULL on error.
> > + */
> > +struct dma_chan *acpi_dma_request_slave_chan_by_index(struct device *dev,
> > + size_t index)
> > +{
> So i think this will be called by client driver to request a channel right?
>
> If so how does client find the device pointer for dma controller.
It doesn't have to. the client passes pointer to it's own device to this
function.
> And index is a global one, right? What is it use ?
It is the index in the client device's ACPI DMA resources. It is explained
in the documentation but it refers to something like:
Device (SPI0)
{
Method (_CRS, 0, NotSerialized)
{
Name (RBUF, ResourceTemplate ()
{
// Bunch of resources...
FixedDMA(...) // This will be index 0
FixedDMA(...) // and this is 1
// More resources..
}
Return (RBUF)
}
}
So we use the index to refer the correct DMA resource in the resource list.
> > + struct acpi_dma_parser_data pdata;
> > + struct acpi_dma_spec *dma_spec = &pdata.dma_spec;
> > + struct list_head resource_list;
> > + struct acpi_device *adev;
> > + struct acpi_dma *adma;
> > + struct dma_chan *chan;
> > +
> > + /* Check if the device was enumerated by ACPI */
> > + if (!dev || !ACPI_HANDLE(dev))
> > + return NULL;
> > +
> > + if (acpi_bus_get_device(ACPI_HANDLE(dev), &adev))
> > + return NULL;
> > +
> > + memset(&pdata, 0, sizeof(pdata));
> > + pdata.index = index;
> > +
> > + /* Initial values for the request line and channel */
> > + dma_spec->chan_id = -1;
> > + dma_spec->slave_id = -1;
> > +
> > + INIT_LIST_HEAD(&resource_list);
> > + acpi_dev_get_resources(adev, &resource_list,
> > + acpi_dma_parse_fixed_dma, &pdata);
> > + acpi_dev_free_resource_list(&resource_list);
> > +
> > + if (dma_spec->slave_id < 0 || dma_spec->chan_id < 0)
> > + return NULL;
> > +
> > + mutex_lock(&acpi_dma_lock);
> > +
> > + list_for_each_entry(adma, &acpi_dma_list, dma_controllers) {
> > + dma_spec->dev = adma->dev;
> > + chan = adma->acpi_dma_xlate(dma_spec, adma);
> > + if (chan) {
> > + mutex_unlock(&acpi_dma_lock);
> > + return chan;
> > + }
> > + }
> > +
> > + mutex_unlock(&acpi_dma_lock);
> > + return NULL;
> in this and error handling you are not doing anything different so why code
> duplication?
There is no specific reason for that. We can change it to goto + return
chan in the next revision.
>
> > +}
> > +EXPORT_SYMBOL_GPL(acpi_dma_request_slave_chan_by_index);
> > +
> > +/**
> > + * acpi_dma_request_slave_chan_by_name - Get the DMA slave channel
> > + * @dev: struct device to get DMA request from
> > + * @name: represents corresponding FixedDMA descriptor for @dev
> > + *
> > + * In order to support both Device Tree and ACPI in a single driver we
> > + * translate the names "tx" and "rx" here based on the most common case where
> > + * the first FixedDMA descriptor is TX and second is RX.
> > + *
> > + * Returns pointer to appropriate dma channel on success or NULL on error.
> > + */
> > +struct dma_chan *acpi_dma_request_slave_chan_by_name(struct device *dev,
> > + const char *name)
> > +{
> > + size_t index;
> > +
> > + if (!strcmp(name, "tx"))
> > + index = 0;
> > + else if (!strcmp(name, "rx"))
> > + index = 1;
> > + else
> > + return NULL;
> > +
> > + return acpi_dma_request_slave_chan_by_index(dev, index);
> are you going to a have a different descriptor for tx and rx? Is index only for
> tx = 0 and rx =1 always. How would a controller be represented which has 8
> channels, each channel can do DMA in either direction
This is a special case so that we can cope with
dma_request_slave_channel().
But this has nothing to do with the controller. This is a client API and
the FixedDMA descriptors are only associated with clients.
For example on Lynxpoint we have a DMA controller you describe above and we
can use dma_request_slave_channel() with that for each client device
(HSUART, SPI and I2C) without problems.
> > +}
> > +EXPORT_SYMBOL_GPL(acpi_dma_request_slave_chan_by_name);
> > +
> > +/**
> > + * acpi_dma_simple_xlate - Simple ACPI DMA engine translation helper
> > + * @dma_spec: pointer to ACPI DMA specifier
> > + * @adma: pointer to ACPI DMA controller data
> > + *
> > + * A simple translation function for ACPI based devices. Passes &struct
> > + * dma_spec to the DMA controller driver provided filter function. Returns
> > + * pointer to the channel if found or %NULL otherwise.
> > + */
> > +struct dma_chan *acpi_dma_simple_xlate(struct acpi_dma_spec *dma_spec,
> > + struct acpi_dma *adma)
> > +{
> > + struct acpi_dma_filter_info *info = adma->data;
> what is the purpose of filter here?
It is pretty much the same as with DeviceTree version. There is an example
of that in the dw_dmac ACPI support patch include in this series.
Basically the controller driver passes the filter (well the
acpi_dma_filter_info) structure to acpi_dma_controller_register(). It can
then do the requred setup for the channel once it is found.
> > +
> > + if (!info || !info->filter_fn)
> > + return NULL;
> > +
> > + return dma_request_channel(info->dma_cap, info->filter_fn, dma_spec);
> > +}
> > +EXPORT_SYMBOL_GPL(acpi_dma_simple_xlate);
> > diff --git a/include/linux/acpi_dma.h b/include/linux/acpi_dma.h
> > new file mode 100644
> > index 0000000..d09deab
> > --- /dev/null
> > +++ b/include/linux/acpi_dma.h
> > @@ -0,0 +1,116 @@
> > +/*
> > + * ACPI helpers for DMA request / controller
> > + *
> > + * Based on of_dma.h
> > + *
> > + * Copyright (C) 2013, Intel Corporation
> > + * Author: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#ifndef __LINUX_ACPI_DMA_H
> > +#define __LINUX_ACPI_DMA_H
> > +
> > +#include <linux/list.h>
> > +#include <linux/device.h>
> > +#include <linux/dmaengine.h>
> > +
> > +/**
> > + * struct acpi_dma_spec - slave device DMA resources
> > + * @chan_id: channel unique id
> > + * @slave_id: request line unique id
> > + * @dev: struct device of the DMA controller to be used in the filter
> > + * function
> > + */
> > +struct acpi_dma_spec {
> > + int chan_id;
> > + int slave_id;
> > + struct device *dev;
> > +};
> is this the representation of Fixed DMA, if so why have you omitted transfer widths?
> I can see obvious benefits of using that
It is, yes. But we haven't been using the widths with our hardware. BIOS
seems to set it always 32-bit even though we should access the peripheral
FIFO using 8-bit transfers for example.
The client never sees these when it uses dma_request_slave_channel() API.
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